Gardening How-Tos – Seasons In A School Garden

A Year in the School Garden

With New Years Day having just occurred, it’s time to start plotting and planning for the gardens. While some periods of the year are busier than others, working in/on the school gardens happens pretty much year-round here in Colorado. Here is an overview of what happens month by month in my gardens. Keep in mind that here in the Denver area, our last frost is typically mid-May and our first frost can occur anywhere from the last week of September to the first week in November, with it typically occurring the first or second week of October.

January

January marks the start of the garden year and is my planning month. This is when I get to curl up on the couch with a blanket, my laptop and the seed catalogs and figure out what we are going to grow and where it will be in each garden. I create maps of the gardens showing exactly where everything will grow and create spreadsheets detailing what, when and who will plant, and order seeds.

February

February is when I ensure that I have all of the materials I need for seed starting. I’ll inventory all of our supplies in storage and then visit our local greenhouse supply store and nurseries to stock up on potting soil, pots, trays, humidity domes and more. Once in hand, I will organize the seeds and other materials so they are ready to go.

At one of the schools I work at, we have an annual Plant Sale where the students grow all of the plants. The plants are all sold via pre-order so that we know exactly how many plants need to be grown. This presale occurs the entire month of February with all orders being made online. Plants are then picked up the Friday before Mother’s Day.

March

We actually get to start growing plants in March by beginning to grow seeds inside under the grow lights. We will start seeds inside beginning in early March and continuing through mid-April. Each seed variety requires a different length of time to grow before being big enough to transplant outside. Each of our seed planting days is scheduled to accommodate the different plants growing needs. Once the seeds are planted, I check on the plants twice a week to water, raise light height, and adjust humidity domes.

Early March	Mid March	Late March	Early April	Mid April
10-12 weeks	8-10 weeks	6-8 weeks	4-6 weeks	3-4 weeks
Eggplant	Peppers	Tomatoes	Marigold	Pumpkin
Parlsey	Chives	Kale	Zinnia	Squash
Celery	Petunias	Basil	Cosmo	Zucchini
Rosemary cuttings	Impatiens	Calendula	Alyssum	Cucumber
Snapdragons			Nasturtium

Seed Starting Timeline

April

April kicks off the busy gardening season with activity happening both indoors and out. Inside we continue starting seeds. Meanwhile, the seeds started in March are now being transplanted into bigger pots and continuing to grow under the grow lights.

Outside, cool season plants that you want to harvest before the end of school can be started in the very beginning of April (you can start the end of March here in Denver, but we wait until students return from Spring Break). In the warm season beds, cover crop is cut down and dug into the beds towards the end of the month.

May

May is the when the outside garden finally begins to take shape. It’s a bustle of activity to squeeze everything in between our last frost free day and the end of the school year. We will typically plant cool season vegetables that will grow over the summer at the beginning of May. In mid May, we will plant some of the hardier plants that have been growing inside. In late May, we will plant the more tender plants from inside.

Early May	Mid May	Late May	Early July	Late July
Carrot *	Parsley	Tomato	Beans*	Lettuce*
Potato	Rosemary	Peppers	Summer Squash*	Radish*
Onion (sets)	Kale	Basil	Zucchini*	Cilantro*
Swiss Chard*	Collard Green	Eggplant	Cucumber*
Collard Green*	Alyssum	Chives
	Calendula	Gourd
	Cosmo	Squash
	Borage	Watermelon*
	Marigold	Swiss Chard
	Nasturtium	Pumpkin
	Sunflower*	Corn*
		Beet*
		Okra
* Varieties planted from seed

Garden Planting Timeline

June

Students get out of school the last week in May or first week in June, so June kicks off summer maintenance. Families from the school volunteer to come in to weed, water as needed, and do pest control. I try to stop by the garden at least once a week so I know what needs to be done and can provide direction to families.

July

In July, summer maintenance continues. Throughout July, additional seeds are planted in the garden. In a typical home garden, these plants are planted in May along with the other plants. However, each of these plants begin producing quickly (30-45 days) and are therefore planted in July so that production begins right about when school starts in late August. The batch in late July are all cool season plants and don’t particularly like to germinate in the heat of July. I always cover the seedlings with shade cloth laid an inch or two above the soil (resting on the edges of the raised beds) to help maintain moisture and cool down the soil.

Garlic that was planted back in November as the garden was being put to bed for the winter is typically ready to harvest in mid-July, while onions are ready in late July/early August. The onions and garlic cure in my garage until school starts and produce distribution begins. The gaps left by harvesting these are filled in with the late July planted seeds.

August

Summer maintenance continues into August. Thankfully, here in Denver, the weeds start to slow down as our energy transitions into harvesting. Typically we start harvesting the first week in August with cherry tomatoes, peppers and greens. School isn’t back in session until the last week in August, so the first couple harvests go to families who are taking care of the garden and/or to families in the community who lack access to fresh food. The first harvest with students typically occurs the very end of August.

September

In September, harvest season is in full gear. We harvest in each garden twice a week. Prior to each harvest, I survey the garden to prioritize what needs to be harvested. Fruits like tomatoes, peppers, eggplant, squash, cucumber, and beans are always harvested when ripe to encourage continued production. “One and done” items like carrots and beets as well as greens can be saved for days when there isn’t a lot of other items to harvest, particularly in the later months.

Both schools that I work at operate Farmers Markets one day a week in September and early October. At one school, all of the produce sold is harvested from the garden. At the other school, produce is procured from an area farm.

October

Harvesting continues throughout the month of October with the harvest becoming more and more focused on cool season produce. Typically in the first week of October, I will put up the frost blankets to cover the cool season produce. This helps to protect it from cold snaps and ensure we will have items to harvest into November.

Once the first frost occurs, the warm season plants die and garden clean-up begins. Warm season beds are cleaned out of all dead plant material and cover crop is planted in its place. The water is typically shut off to the gardens in early to mid-October and everything must be hand watered for the rest of the season.

November

With the use of frost blankets, the cool season produce stays growing through mid-November and we continue harvesting. Harvesting at a rate of two classrooms per week, this extended harvest time allows every classroom in the school to participate in a harvest day. If we desired to, we could even extend this harvest longer. But it becomes more and more difficult to organize an entire classroom to harvest when you’re working around snow and cold temperatures. This past year, our temperatures dropped to 14°F on October 30. Through a combination of two layers of frost blankets (one laid directly on top of the plants the second over the hoop frames) and a final layer of clear plastic, the plants all survived this cold. Once all classrooms have harvested, the remaining beds are cleaned out, and garlic and cover crop is planted. I continue to water the cover crop on a weekly basis as long as the temperatures are above 45°F and there is no snow on the ground.

December

December tends to be the only down month in the school garden. By this time of year, I am ready for a break and the only activity in the garden is the occasional cover crop watering. Otherwise, the gardens (and myself) take a much needed break through the next several months.

Square Foot Gardening in the Schoolyard

Note the white string marking square foot sections in the center of the front bed. The onions had just been harvested and we were preparing to plant radishes in their place.

Square Foot Gardening is a popular method of organizing and planning a vegetable garden. It provides an efficient way to grow large amounts of vegetables in a small space. Its core idea is that the garden is divided into square foot sections and that a certain number of each vegetable can be grown in each square foot. I find this method an easy way to plan and plant a garden with students. It allows them to easily visualize the garden, how much space each plant needs and how many plants can realistically fit into the garden. Then on planting day, the square sections provide an easy way to identify where plants go and to divide labor amongst the students.

When I have students plan the garden, they first start by measuring the garden and drawing a map. The map is drawn on graph paper so that every square foot in the garden is represented by one square on the graph paper. You can create custom graph paper online so that the squares are a reasonable size for your students to use. Then they get to decide what goes into each one of the squares. Based on how much space each plant needs to grow, Square Foot Gardening developed a list of how many plants fit into one square foot. I like to provide a custom template designed for that particular garden so that the students have a key to use as they fill in the squares. The template shows what plants are available to plant and how many fit into each square. Students can cut out the template and glue them onto the map or they can draw them onto the map. I have even drawn a scale map on the classroom floor using masking tape to outline the edges of the bed (one a 1’ equals 3” or 4” scale) and the square foot sections and made cutouts out of construction paper so that students could easily manipulate the plan. When I do it on my own, I use Microsoft Visio on the computer so that I can easily drag and drop the squares into the space.

Once the square foot plan is created, you can practice some basic math problems:

We have four squares of carrots with 12 carrots in each square. How many total carrots do we have?
What fraction of our garden is planted in carrots?

In the official Square Foot Gardening method, they recommend using wooden grids that are laid on top of the soil to divide out the garden. Instead, I use cotton string that is anchored at the edges using garden staples. It’s time consuming to lay out but is cheaper than building them out of wood and I don’t have to find a place to store them over the winter. The grids come in handy on planting day, particularly for closely spaced seeds. I don’t find it as useful for large plants like tomatoes that take four full squares per plant. Each student is assigned to plant a single square foot. The grid allows them to easily identify the edges of their planting area and defines exactly how many plants/seeds will get planted into their section. I often define their planting areas even farther by using colored flags or colored popsicle sticks to define what gets planted where (pink flags are for carrot seeds, blue flags are for beet seeds, etc.) and by pre-making the holes using a muffin tin. To help students easily find their square, you can also label each garden bed as a coordinate grid.

Another benefit of Square Foot Gardening is maximizing your area to grow a lot of food in a relatively small space. Unlike traditional farming systems or large in-ground gardens where you need space to walk in between rows, square foot gardening bumps plants right up next to each other, giving each plant the exact amount of space they need and no more. Below you’ll find a list of the plants we grow and how much space they need. Additionally, you can use trellises to grow vining plants upward to maximize the space even more. I use trellises (cattle panels from an agricultural supply store zip tied to rebar posts sunk into the ground) on the obvious vining plants like pole beans and peas, but also plants that typically spread out a great deal like cucumber, smaller winter squash (acorn, delicata, gourds, mini pumpkins) and melons. I make diligent use of tomato cages for not only tomatoes, but also taller pepper plants and eggplants to help force the growth upward and not outward. All of this compacted space pays off. Last year we grew just over 500 pounds of food in under 400 square feet.

Plant Spacing for Square Foot Gardening

Plant	Spacing
Arugula	Scattered seeds
Basil	4/square foot
Beet	9/square foot
Carrot	12/square foot
Chives	2/square foot
Cilantro	4/square foot
Collard Greens	1/square foot
Corn	4/square foot
Cucumber	4/square foot on trellis (2 on each side of trellis)
Eggplant	1/square foot
Garlic	4/square foot
Head Lettuce	4/square foot
Kale	1/square foot
Mesclun/Salad Mix	Scattered seeds
Okra	1/square foot
Onion	4/square foot
Oregano	1/square foot
Parsley	2/square foot
Peas	6/square foot on trellis (3 on each side of trellis)
Pepper	1/square foot
Pole Beans	6/square foot on trellis (3 on each side of trellis)
Potato	1/square foot
Radish	12/square foot
Rosemary	2/square foot
Sage	1/square foot
Summer Squash	1 plant/4 square feet
Swiss Chard	4/square foot
Thyme	1/square foot
Tomato	1 plant/4 square feet
Winter Squash	4/square foot on trellis (2 on each side of trellis)

The one part of Square Foot Gardening that I don’t follow is their soil mix. They recommend a do-it-yourself mixture of 1/3 compost, 1/3 peat moss and 1/3 vermiculite. Here in Colorado, this mix just dries out too quickly and the materials aren’t very sustainable. If we need to fill new beds, I will use a planters mix (50% topsoil, 50% compost) from our local organics recycling company. If you are ordering from somewhere, be sure to check out their product first. I’ve seen way too many “raised bed soils” that are way too heavy and filled with coarse, heavy materials to work well. Also, instead of replacing the soil every year as the Square Foot Gardening method recommends, we use regenerative practices such as minimal till, cover cropping and adding compost to keep the soil healthy and fertile.

I honestly cannot imagine gardening in a school environment any other way. It just makes sense from a planning, logistics and production perspectives. If you’re not already familiar with it, I encourage you to read more. It’s not really that difficult to figure out and the payoffs are huge!

Carrot seeds sprouting inside a square foot

Planting Seeds with Students

Planting seeds with a group of students looks quite a bit different than when I sit down and plant seeds all by myself. It’s even different from when I plant seeds with my daughters. Having a large group of students changes the dynamic and flow of the activity. As any teacher knows, successful activities in the classroom are made or broke by how you set up the activity and seed starting is no exception. Over the years I’ve developed a set of techniques and strategies that sets the seed planting up for success. Here are the things I recommend for anyone planning to plant seeds with a group of students.

PREP MATERIALS AHEAD OF TIME

This one probably goes without saying, but the more I can have prepped ahead of time the smoother the planting will go. Prior to even starting our seed planting sessions, I do the following set-up.

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Label pots and trays semi-permanently. Each and every pot we use is labeled with a small dot sticker that has the name of the plant printed on it. These are fairly waterproof and don’t peel off very easily. The dot stickers will come off when soaked in water (i.e. when were cleaning and sterilizing the pots after use) but otherwise stay on really well, even during robust watering sessions. The trays are also labeled with a sticker so it is easy to see what is growing in the tray.

Transfer seeds to containers. I transfer the seeds from the seed packet into half cup storage containers with lids. This allows students to easily help themselves to seeds and minimizes spillage. I typically have one container for every 4-6 students. Each container is labeled with the same sticker as the pots in order to minimize mix-ups.

Put soil in a long, short container. I like to use under the bed storage containers to hold the soil. This allows multiple students to easily access the soil at one time. The 41 quart size is a perfect size to allows me to easily handle the tub. With one soil tub in the center of a 6’ table, 6-8 students can gather around the table and have access to the soil. With two of these tubs on a table, 10-12 students can gather around. Depending on the group of students and how complicated our planting is, sometimes I use two tables with one tub on each and sometimes I use one table with both tubs on it.

Put a lid on your soil. Students love putting the hands in the potting soil and moving the soil around. It is a great sensory experience for students, but it means that the soil gets spilled and the students aren’t listening to instructions. I take the lid off only when students are filling pots with soil. For this reason, I like to have a lid that is easy to get off and on.

Cover your table with a light-colored tablecloth. A tablecloth helps make clean-up go smoother. The light color makes it easier to see spilled seeds. I prefer using a heavy-duty vinyl tablecloth as the lighter duty plastic tablecloths get torn by the students fiddling with it. I use bedsheet straps under the table to hold the tablecloth in place. Anything on top or along the edge of the table gets fiddled with by the students.

HAVE A PLANTING ROUTINE

Just as the set-up matters, how I go about planting the seeds ensures that the seeds are planted correctly.

Control your group size. Ideally I like to plant with 8-10 students at a time, although I can manage with 12-14 students. When it goes above this number, I can’t easily keep my eyes on all students to ensure that they are correctly planting their seeds. If this is your first time planting with a group, I would start small with 4-6 students at a time.

Have an additional activity. I typically work with one classroom of students at a time. Half plant with me while the other half is doing an independent activity. This independent activity keeps them engaged exploring seeds and planting while I am planting. If I am working in just one classroom, the class can be doing normal classroom work independently while I call up small groups.

Talk about the holes in the bottom of the pot. I always start planting by showing students the pot and asking them what they notice. The holes always come up. I explain the holes by asking what would happen if their head got stuck underneath the water – they couldn’t breathe and they would die (drown). Then I explain that plant roots are the same way and if they get stuck under the water for a long time, the plant can’t breathe and it will die. The soil in the pot sucks up water like a sponge, but it can’t hold an endless amount of water. If too much water is added, the extra water comes out the holes so the plant can grow.

“When you’re filling the pot with soil, the pot stays in the soil tub.” I always repeat this several times so students understand. It helps keep the soil contained in the tub, otherwise the soil overflows the pot and ends up all over the table (and the floor, and the students….).

“When you’re putting the seed in the pot, the pot goes on the table.” Once students have filled their pots with soil, the pot goes on the table and the lid goes back on the soil tub. Then I give them a tub full of seeds. This prevents seeds from being spilled into the soil tub. I learned this one the year that someone sprinkled/spilled basil seeds into the soil tub and every plant after that had basil sprouting up next to it. I pulled so many basil sprouts that year!

Minimize putting seeds into holes. Students love to make holes and they are quite often too deep for the seed meaning the seed doesn’t have enough energy to make it to the top of the soil. Only the biggest seeds (squash family and nasturtium) get holes when we plant. The rest of the seeds (¼”- ½” of depth) are placed on top of the soil in the pot and then some soil is pushed over from the side of the pot to cover it up and gently patted down. Seeds that need ½”-1” of depth get a hole made by one finger pushed into the soil that stops when the first knuckle starts going into the soil. We find this knuckle together as a group before we begin.

Demonstrate what to do. Showing students what to do is worth a thousand words. As I work, I have students put their hands behind their back so that they aren’t tempted to start playing in the soil. I start by filling the pot with big handfuls of soil and pushing the soil down hard (not superhero hard) with my fingers. Then I emphasize putting the pot on the table to put the seeds in. I’ll emphasize how many seeds we’re planting and then take more seeds than I need and place them in my palm. Then I count how many seeds I have and put back the extras I don’t need. I place the seed(s) on top of the soil and show them the seed so they can see it on top. Then I push a little soil from the side of the pot with a big flourish to emphasize and exuberantly pat the soil on top of the seed.

Use checkpoints to ensure students are doing it properly. As we work through the planting process, I am constantly checking on the students to make sure that they are correctly following the steps. I’ll hold the entire group from progressing to the next step until I’m sure everyone is on track. Before I take the lids off the seeds and we start actually planting, I make sure that everyone has the correct amount of soil and it is properly packed down. Once everyone has done that, we put the lid on the soil tub and the seeds come out. As students are working, I try to look to see they have the correct number of seeds. As they bring their pot to the tray, I make sure the seeds are covered up.

Clean up the soil on the table in between groups. I keep a dustpan handy to sweep the soil from the table away. Kids love moving the soil around and the sound of their hands and soil moving around on the tablecloth is noisy and distracting. Plus having a clean tablecloth makes it easier to see and salvage seeds when they get spilled. Because seeds do get dropped and spilled in this soil I always dispose of this soil in the compost or trash rather than putting it back into the soil tub. Otherwise, I end up with mystery plants sprouting adjacent to my known plants.

While it seems like a lot of work for you and somewhat controlling for the students, there is lots of room for error in planting. Over the years I’ve learned from my mistakes and this process really helps eliminate most of that error. Most of our seeds germinate with the plant that should be in the pot, only one plant sprouts and the seed is centered in the pot. The students still get the opportunity to feel soil between their fingers and to witness the process of a tiny seed sprouting and growing something amazing. It is such a different experience from the typical day to day classroom routine and they look forward to planting each and every time!

How to Successfully Start Seeds

For many years I avoided starting my own seeds. I told everyone it was because we didn’t have the space in our 1300 square foot house, but really it was because I lacked the confidence to do it right. I tried starting seeds over 20 years ago on the floor below a south facing window and within a matter of two days all the seedlings had shriveled at the base and fallen over like a tree that was chopped down. I now know that my seedlings suffered from damping off, a soil-borne fungal disease that quickly spreads through your seedlings. I could have prevented it by using the proper sterile soil (not soil that had been in a bag on my porch for a year) and making sure my equipment was sterile as well. Even with that knowledge in hand, it was enough to keep me from starting my own seeds for 15 more years. All that time, I worked alongside the experts at Denver Botanic Gardens and learned the basics of seed starting. While I wasn’t starting seeds myself, I was still teaching and inspiring others to do it. I transferred that knowledge to students in after-school garden clubs I ran where we started seeds and to teachers taking professional development classes who then successfully grew seeds in their classrooms. But I still I wasn’t ready to start my own.

Over 800 plants growing in my dining room during the Covid lockdown

It wasn’t until five years ago when I took over the garden coordinator role at a school and successfully grew over 1000 plants that first year. The fear stayed though – I would wake up in the middle of the night having dreamed that all of the seedlings had pitched over like a falling tree. The next year we started our seed starting efforts in early March, only to be interrupted two weeks later by a “three-week extended spring break” due to the Novel Coronavirus. I took a grow light shelf home along with five flats of seedlings expecting to bring them back three weeks later. Well, we all know what happened to the three-week extended spring break! The five flats ballooned into 20 and I ended up growing over 800 plants in my dining room in order to fulfill all of the orders for the school plant sale we had taken back in February. Leveraging on that success, I was able to carve out space in our small house to grow a total of five flats on top of the washing machine, dryer and adjacent windowsill three years ago. Needless to say my fears are gone! I started my fifth season of seed starting last week. I anticipate growing over 900 plants at one school, 150 at a second school and about 60 at home this spring. My excuse is gone, my confidence is solid and I’m here to share the really simple basics of seed starting with you.

Successful seed starting really comes down to making sure you have the right equipment. You can find a detailed why for each item and some suggested products here. Once you have that, it’s as simple as soil, seed, water and light. So spend some time sourcing a grow light, good seed starting soil, sterile pots and trays, humidity domes and a heat mat. And learn from my mistake 22 years ago, make sure everything is sterile. I reuse pots, trays, and humidity domes year after year, but only after they’ve been scrubbed clean, and they’ve sat in a bleach solution (1 part bleach: 9 parts water) for 10-15 minutes. You can put together a simple seed starting set up for two flats (~60 plants) for about $50. When you compare that cost to purchasing the plants from a nursery at $4-10 a piece, it really is more cost effective.

From the top down, here is how you’ll set up your system:

Grow light
Humidity dome
Pots
Tray
Heat mat

Once your equipment is set-up, you’re all set to plant, but it won’t be all at the same time. Different plants need different amounts of time to grow prior to transplant, so you’ll need to pay attention to the seed packet and follow their timing recommendations. You can calculate when to start your seeds by determining your average frost free date and then counting backwards the number of weeks from there. Here is a general breakdown of timing:

10-12 weeks before last frost: eggplant, celery, onion, rosemary, chives, snapdragons, petunia
8-10 weeks before last frost: peppers, mint, parsley, coleus, impatiens,
6-8 weeks before last frost: tomatoes, basil, calendula
4-6 weeks before last frost: kale, collard green, swiss chard, broccoli, cauliflower, basil, marigold, zinnia, cosmo, nasturtium

Also keep in mind that some plants grow best when the seed is directly planted into the garden (called direct sowing). Either they grow so quickly that they don’t need an advance start or they don’t like having their roots disturbed. These include plants like carrot, beet, turnip, radish, cucumber, melon, squash (summer and winter), zucchini, pumpkin, peas, beans, lettuce, spinach, and arugula. Don’t waste your time starting these ahead. Just wait until the soil is the right temperature and plant outside.

When it’s the appropriate time to plant your seed, follow these simple steps.

Fill the pot with soil. Use your hand to fill the pot and then two or three fingers to push the soil into the pot. The soil gets filled with lots of air space when moved into the pot and then will settle over time leaving just a small amount of soil. Pushing the soil down compresses the soil ahead of time and ensures you have a proper amount of soil. Don’t push so hard though that all of the air space is squeezed out. I like to tell students to push hard, but not superhero hard. Make sure you’re using a sterile soil that is designed for seed starting.

Plant the seeds. For small seeds, place one seed on top of the soil in the center of the pot. For large seeds, make a hole twice as deep as the seed and put the seed in the hole. Sprinkle soil on top of the seeds to cover them up. Small seeds need just ¼” of soil on top. Some seeds like petunia, coleus, snapdragons, and impatiens should not be covered up at all, but left on the surface of the soil.

Place pots in a tray. Place all of your pots in a tray without holes.

Water the tray. Using a watering can, fill your tray approximately halfway with water. The soil will absorb the water through the holes in the bottom of the pot. If you water directly on top of the soil you risk splashing the soil and seeds out of the pot. Plus it takes a lot less time to water one tray than 72 individual plants. Check on the tray after a few hours. If no water remains and the top of the soil is still dry or semi-dry, add more water. If the water is gone and the soil looks saturated at the top, leave as is.

Cover with a humidity dome. Seeds need a consistent moisture level in order to germinate. A humidity dome traps the evaporated water and then rains it back down on the soil. This keeps the seeds and soil a consistent moisture level. It also means you don’t need to water as frequently.

Heat the soil. Many seeds germinate best when the soil temperature is 70-90°. A heat mat placed under the tray will raise the temperature of the soil above the ambient temperature of the room resulting in better and quicker germination. Seeds that like it warm include: tomato, pepper, eggplant, parsley and zinnia.

Provide bright direct light. Place your seed trays underneath a grow light that is positioned 3-5” above the top of the soil. Set the grow light on a timer so that you have 14-16 hours of light per day.

Depending on the plant type, your seeds can sprout in as little as 3 days (zinnia and marigold) or it may take 3-4 weeks (eggplant, parsley, pepper, celery).

The seeds will sprout and have one or two leaves. These are called cotyledon leaves and served as the plant’s food storage for the initial growth. The next leaves and all subsequent leaves are called true leaves. The true leaves photosynthesize to make food for the plant. Once this sprouting has occurred, continue with the following:

Maintain moisture. Make sure that your soil remains moist (not saturated) until the seeds sprout. With the humidity dome on, you may not need to water at all. If there is no water collecting on the inside of the humidity dome, it is time to place 1/4”-1/2” of water in the bottom of the tray. When you water, the water should be fully absorbed within 1-2 hours. If it doesn’t all get absorbed, dump out the extra water. Once the seeds have sprouted it’s okay to let the surface of the soil dry slightly in between watering. Every few days, you will need to put 1/4”-1/2” of water in the bottom of the tray – enough for it to absorbed within a few hours.

Basil seedlings ready to be thinned to one per cell

Thin seedlings. Ideally you should have one plant growing per pot. If you ended up with more than one plant, you should remove the additional plants so each plant has enough space and access to water, nutrients and light. When thinning, try not to disturb the root system of the adjacent plant. The best way to accomplish this is to use a pair of small scissors (nail scissors work great) to cut the plant at the soil level. You can also gently pull out the seedling. Some plants like chives and alyssum are planted with multiple seeds per pot and do not need thinning.

Remove the humidity dome. Once the plant has two sets of true leaves, you can begin to wean the plants from the humidity dome. Prop up a corner of the dome and leave it propped open for a few days before you remove the humidity dome entirely.

Varying light heights on the different trays

Adjust the light height. As the plants begin to grow taller you will need to raise the height of the grow light. The light should be 3-5” above the tops of the plants at all times. If the light is too far away, the plants will grow quickly to reach the light and won’t have as strong of stems.

Transplant into larger pots. When the plant has 3-5 sets of true leaves, you can transplant them into a bigger pot. For many plants this act of transplanting disturbs the roots slightly and encourages the plant to grow more fine roots for absorbing water. This is why you start seeds in a small pot and move them to bigger pots. Some plants do not like to be transplanted though and should be started in a bigger pot.

As your seedlings continue to grow, monitor the moisture level and light height on a regular basis. As you get closer to your frost free date, you will need to transition the plants to the outside. This is called hardening off. Plants that go from the consistent warmth of inside to the variable nature of outside are in for a shock and need to slowly adapt to the new environment. Begin by putting your seedlings outside in the shade for a few hours then bringing them back inside. The next day put them in the sun for an hour and then move them into the shade, bringing them back inside after a few hours. Increase the length of time in full sun and the total time outside each day until they’re spending the full day in the sunshine. After 7-10 days you can leave the plants out overnight, as long as your nighttime temperatures are above 50°. If you have a cold day during this period of time, leave the plants inside.

Once your plants are hardened off, you’re past the danger of frost and nighttime temperatures are warm, its time to transplant your plants into the garden. Make a hole the same depth as the pot and twice as wide. Gently remove the plants from the pot, spread the roots apart at the base, place in the hole and backfill with the soil you removed.

While I know this seems like a lot of steps, it really isn’t that hard. Just make sure you start with clean equipment and provide adequate moisture and light. Soon you’ll be harvesting food for dinner and be filled with pride knowing that you grew this all by yourself!

Essential Seed Starting Equipment

This morning I stopped by one of the schools that I work at to take inventory of our seed starting equipment so I could purchase anything new that was needed. Thankfully we don’t need much other than soil this year!

Over the years I’ve homed in how to start seeds in a school. Even though we lack a greenhouse, we’ve made it work for many years now growing seeds in the atrium in between hallways. Last year we grew over 1100 plants at this school in a space about 12’ wide by 3’ deep! While most schools won’t be growing this many plants, there are some basics that I would consider essential for any seed starting set-up.

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Light source

Even the biggest, brightest south facing windows won’t provide enough light to produce healthy flowers, herbs and vegetables. You can certainly grow plants without supplemental light, but they will be super tall with lots of space between leaves and weak stems (these are called “leggy” plants) and likely won’t transplant well into the garden. There are many different options for light sources depending on how much you want to grow. The most important thing to consider is that the light source has a flexible height adjustment as you want your lights to be about 3-4” from the top of the plants at all times. There are so many different grow light options, here are a few to consider.

This is the setup one of my schools uses that allowed us to grow 1100 plants last year. We have several sets of 6’ tall commercial metal mesh shelves set up to have five shelves (we grow plants on four shelves and store supplies on the top shelf). Each shelf holds 4 flats, for a total of 16 flats per unit. Hanging from the underside of each shelf are two 4’ long shop lights, holding two fluorescent bulbs each. The chains on the lights attach to the shelf with an s-hook. This allows me to adjust the height of the lights. It’s cumbersome to change the height, but doable. We use just plain old fluorescent lights, rather than the more expensive grow lights. Grow lights emit light in the red and blue spectrums, while standard fluorescents contain a broader portion of the light spectrum. The exact portion of the spectrum depends on the warmth and color of the lights. I’ve used both grow lights and standard fluorescent and haven’t noticed a difference between the two, other than standard fluorescent are significantly cheaper. At some point I’d like to convert our fluorescent fixtures to LED fixtures, but for now it’s too cost prohibitive.

This clip-on LED light strip is the easiest and cheapest option and is what I use at home. Each clip on comes with four light strips. My plants are placed underneath a south window, so I am able to use just two light strips per flat and can therefore accommodate two flats per light unit. It has a built-in timer and you can turn on one, two, three or all four of the light strips.

For a small set-up or a dispersed set-up, the Jump Start Grow Light System is super easy to use. This is what I recommended schools use for many years before LED lights became more readily available and they are still a great option. This is also a nice option when you want to spread out the seeds among numerous classrooms. The lights are very easy to adjust in height and the whole system easily comes apart for storage in its original box. You can fit four flats underneath the 4’ model, giving you space to grow almost 300 plants, depending on what size pots you are using. The 2’ model fits two flats and up to 150 plants.

Pots

Seed starting and nursery pots come in a variety of sizes. It’s best to start your seeds in small pots like a small four-pack. You can also use six-packs, but I like the flexibility that four-packs provide. Then when they have at least two sets of true leaves, you can transplant them into a larger pot. The act of transplanting helps to stimulate finer roots to grow and results in healthier plants. For a school’s needs, you typically don’t need to transplant any larger than a 2.5” pot. As part of our plant sale, we offer flowers in four-packs. In this case we start and finish the seeds (no transplanting) in a large four-pack. Some seeds (squash family, root crops, celery, corn) don’t like their roots being disturbed during transplanting into the garden. I prefer to direct seed these plants into the garden, but if you must start them inside it is best to use peat pots where you can plant the entire pot to avoid root disturbance. I use peat pots only when necessary as they are more difficult to work with. You can typically buy all of these pots in small amounts at a local nursery or in bulk from a greenhouse supply store. We reuse the pots from year to year, cleaning them out and bleaching them after use so they are sterile for the next year.

Soil

If you’ve ever gone to buy soil by the bag, it can be a bit overwhelming as there are many different kinds of mixes available, each with a different purpose in mind. For seed starting you absolutely want a mix designed for seed starting. These mixes are made with a variety of fine ingredients that allow for fine roots to easily grow, contain organic material to feed young plants, and optimize water retention without becoming soggy. Oddly enough, these mixes don’t actually contain any soil, which by definition is decomposed rock particles, but have a variety of organic materials. The kids always ask what the white stuff is – it is called perlite and is a volcanic rock. Perlite has low water absorption and helps prevent compaction of the soil. I like to use ProMix Organic Seed Starting Mix. This works great and it doesn’t contain any chemical fertilizers for students hands to come in contact with (our state child care licensing prohibits this for preschool programs). This is also available in large compressed bales from greenhouse supply stores, sold as Pro-Mix MP Mycorrhizae Organik.

Flats

Using greenhouse flats without holes is critical to a seed starting system where water cannot drip on the floor. They not only act as a saucer to keep water from spilling on the floor, they also serve as the method in which to water your plants. I always bottom water the seeds filling the tray up with about one inch of water every 2-3 days or whenever the soil starts to dry out. This keeps newly planted seeds from washing away and is much easier than individually watering 1000 plants! This type of tray is available in varying thicknesses. The thinnest ones are flimsy and are hard to move around when there is water in them – they would work well in a stationary environment, but don’t hold up when you’re sliding trays in and out of shelves. The thickest ones are very sturdy, but they are more prone to breaking (and leaking). I’ve found the middle of the road ones (1.8 mil thick) to be the best. These TO Plastics 1020 trays are an industry standard.

Humidity Domes

Humidity domes are a key component of success when growing seeds outside of a greenhouse. Once a seed gets wet, if the seed dries out, it can no longer grow. So, maintaining consistent moisture prior to germination is critical. Humidity domes act like a miniature atmosphere trapping the water that has transpired (i.e. evaporated) out of the plants and then dropping it back down onto the plants. After I plant seeds and water from below until the soil is wet, the humidity dome traps most of that water and I don’t have to water very frequently. I typically keep the domes on until the plants have 3-4 sets of true leaves. The humidity domes shown are 2” tall and perfect for this use case. They also sell 7” tall domes which are great for if you have to leave your seedlings for an extended period of time without water (i.e. Spring Break). Once the seedlings are big enough to remove the domes, I slowly wean them away from the high humidity environment by propping up the edges along one side for several days. I’ve found Duplo blocks work perfect for this.

Heat Mat

Some plants prefer cool temperatures for germination, while others prefer it to be warm. Plants in the nightshade family (tomatoes, peppers, eggplants), squash family (pumpkin, winter squash, melons) and certain herbs (basil, parsley, rosemary) prefer soil temperatures of 75°-90° for germination. Unless your school is really warm (and I’ve been in classrooms that are 80° year-round), you will likely need a heat mat to achieve decent germination with these plants. These are easy to use, you simply plug them in and put the flat on top of it. They raise the soil temperature 10°-15°. You can’t control the exact temperature, but I’ve never found that to be a problem. Alternatively, if you’re in an old school with a radiator, you can sometimes place your plant trays on top of the radiator panel to achieve this increase in temperature.

Water

I love having students involved in watering the plants, which means having a watering can that they can easily handle. Ikea’s PS 2002 watering can is the perfect size for students. It easily fits under a water bottle filing station or sink and is light enough for students to carry and maneuver. They do have an open top though, so students have to walk slowly to avoid spilling water. When I water alone, I choose a 2-3 gallon watering can with a small spout on it.

As I mentioned before, I always bottom water filling the tray underneath the pots up with water rather than pouring the water on top of the soil. The soil absorbs the water and moves it up through the pot through osmosis. We water every Monday, Wednesday and Friday, adding water to trays that are dry. I like to draw a silver line about 0.75” up from the bottom of the tray to mark where the water should stop. One of the Ikea watering cans is typically enough for one tray.

With this equipment on hand, it is possible to grow just about everything for your garden from seed. It can be expensive making the initial investment in the equipment, but most of it is reusable and your cost in subsequent years is just the cost of seeds. This year I spent $175 on seeds in order to grow 900 plants from seed and over 500 plants that we will direct sow in the garden. If our garden produces 500 pounds of food like last year, this equates to $0.35 per pound in plants (the cost of labor and other equipment is not calculated into this). Not bad for a small school garden!