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  • JoAnna

Two Easy Ways to Make Seed Starting Trays

Updated: Sep 2, 2021




Growing your own food is a great way to reduce waste. Even if you already use reusable produce bags and take other measures to reduce your waste at the grocery store, producing food at home reduces the “upstream” waste involved in growing, shipping, and transporting food from farm to store. So regardless of whether you have room for a huge in-ground garden or only have space for a few patio pots, anything you can grow yourself is a win. For our household, we’re currently opting for a large container garden inside of a greenhouse.


How to get started? With seeds of course! Rather than buying pre-started plants from the nursery, which usually come in disposable plastic pots, I’ve found that starting my own seeds is the best way to reduce waste and save money. Instead, I like to use biodegradable seed starting pots that can be transplanted directly into the garden, seedling and all. As an added bonus, starting from seed gives you a lot more flexibility to choose from a variety of organic and heirloom varieties of plants better suited to the local environment.


(If you are ready to get started, jump to instructions here.)


Here in Montana, the growing season starts a little bit later than it does in much of the lower 48 (especially where we live at above 5,000 feet elevation)! I finally felt safe to start our seeds indoors during the first week of May, though most of our little babies probably won’t move out to the greenhouse until at least June 1st. It isn’t uncommon to get snow in June here. There’s even an old picture of my siblings and me standing ankle-deep in the snow on the first day of summer vacation! Despite the challenges of protecting our plants from frost, I still prefer gardening in Montana to gardening in Louisiana, where we had to deal with every pest under the sun, hurricane winds, and flooding. But I digress… Back to the task at hand!


The weather here is also very dry, so in addition to keeping our little seedlings warm, we need to keep them from drying out. When faced with these types of challenges, many people turn to store-bought plastic seed trays with clear plastic tops to act as little mini-greenhouses. Some of these seedling trays even come in “self-watering” designs. For these designs, a piece of absorbent material rests in a tray above a reservoir of water. Seed starting pots sit on top of the material and the material wicks up water from the reservoir and in turn, keeps the seedlings in the containers from drying out. Pretty clever!


My mission: recreate this design in a Zero Waste waste way.


Because while those store-bought containers do work well to create a warm and humid environment for sprouting botanical bundles of joy, they are also, of course, plastic. Some people buy them and are able to use them over and over again. I am not one of those people. I always manage to damage/break/lose mine from year to year (Is my garage eating things? I swear it’s eating things!), so I prefer an alternative that repurposes existing plastic or doesn’t use plastic at all.


In a sort of impromptu experiment, I came up with two simple designs. For the first, I created mini-greenhouses by repurposing those plastic clamshells used for leafy greens. For the second, I created extremely unfancy self-watering trays using baking sheets. For both designs, I incorporated some craft felt I had on hand to absorb and wick moisture in the bottom of the tray to keep the seedlings from drying out. I also purchased some inexpensive biodegradable seed starting pots. I love these because they are sturdy, but they can be planted directly into the garden, which protects the seedlings’ developing roots from damage during transplanting.


I also used a seed starting mix to give the seeds a healthy start. If you’ve been composting for a while, creating your own seed-starter mix is a great way to use it. Otherwise, you may need to purchase some organic seed starting mix. To make your own you can use a mixture of compost, perlite, vermiculite, and peat moss (there are variations, but a basic recipe would include 4 parts compost, 1 part perlite, 1 part vermiculite, and 2 parts peat moss).


The exact amount of supplies you will need depends on how many seeds you plan to plant. But in general, to create your own extremely unfancy but functional seed starting trays, you will need:



Supplies:

  • Biodegradable Seed Starting Pots

  • Organic Seed Starting Mix (either store-bought or homemade)

  • Seeds (Preferably organic and/or heirloom seeds suited to your environment. I planted peas, bush squash, zucchini, tomatoes, kohlrabi, and a variety of herbs and lettuces).

  • Crafting Felt or other absorbent fabric (enough to line the bottom of the tray or clamshell)

  • Plastic clamshells leftover from lettuce, berries, etc. (if going with the upcycled clamshell design)

  • Cookie sheets or glass baking pans (if going with the baking sheet design)

  • Compostable/Worm Farm Friendly Saran Wrap (optional for baking sheet design).



Instructions for the Clamshell Greenhouses:


  1. If your clamshell doesn’t already have holes in it, use a pen or other pointy object to poke a few holes in the top and bottom of the container for drainage and air circulation.

  2. Line the bottom of the container with felt. An unused sweater made of cotton or wool would also work here. The fabric will absorb water and help to keep your seedlings from drying out during the day.

  3. Put your biodegradable pots in the clamshell on top of the felt. Fill them with seed-starter mix. You can purchase seed-starting mix or make your own using a mixture of compost, perlite, vermiculite, and peat moss (there are variations, but a basic recipe would include 4 parts compost, 1 part perlite, 1 part vermiculite, and 2 parts peat moss).

  4. Plant a few seeds in each pot (you can thin them out once they start to grow). I generally plant 2-3 “bigger” seeds like Zucchini or tomatoes per pot and sprinkle in about 5-7 seeds per pot for lettuces and herbs. Some of those darn seeds are so small you can barely count them! How deep you plant depends on the type of plant. The Spruce has some basic guidelines in case you aren’t sure.

  5. If you’re worried about leaking, place the clamshell on top of a towel, plate, cookie tray, or something else that will catch any drips.

  6. Gently water your seeds so that the seed-starting mix becomes wet but not totally soaked (I say gently because if you dump the water in too quickly you may accidentally wash your seeds out of the pot. If kids are helping--which I hope they are!--you may have to rescue a few seeds from a watering-can flood).

  7. Make sure to also wet the felt so it absorbs water and can give the plants moisture from below. This will keep the seedlings from drying out and help them go longer between waterings.

  8. Place your little greenhouses in a warm, sunny location to germinate and grow. I closed the top of my clamshells to keep things nice and humid but depending on your environment, you may want to leave the tops a little bit open. Once your seedlings get tall enough, you’ll want to leave the clamshell open so they don’t press against the top.


Instructions for baking sheet Greenhouses


  1. Line the bottom of the baking sheet or baking pan with felt. An unused sweater made of cotton or wool would also work here. The felt will absorb water and help to keep your seedlings from drying out during the day.

  2. Place your biodegradable seed starting pots on top of the felt and fill them with your seed-starting mixture. You can purchase seed-starting mix or make your own using a mixture of compost, perlite, vermiculite, and peat moss (there are variations, but a basic recipe would include 4 parts compost, 1 part perlite, 1 part vermiculite, and 2 parts peat moss).

  3. Plant a few seeds in each pot.

  4. Gently water your seeds so that the seed-starting mix becomes wet but not totally soaked (I say gently because if you dump the water in too quickly you may accidentally wash your seeds out of the pot).

  5. Make sure to also wet the felt so it absorbs water and can give the plants moisture from below. This will keep the seedlings from drying out and help them go longer between waterings.

  6. Place your little greenhouses in a warm, sunny location to germinate and grow.

  7. Because there are no holes in the bottom of the tray for water to drain out of, you may not need to cover the top of your seedlings with anything to keep them from drying out. However, if you find they do need more moisture and humidity, you can cover them with biodegradable saran wrap which will create a warm and humid greenhouse environment (I did not end up needing to do this).


For both types of greenhouses, keep an eye on your seedlings and add more water when you stick your fingertip into the soil and find that the top layer has dried out (or anytime they start looking wilted). Gently water (you can also use a spray bottle to mist them a bit) and be sure to continue to wet the felt at the bottom as well.


Don't feel like you have to make your seed trays exactly the way that I did if you don't have these same things on hand. Instead, I encourage you to use this as a general outline and instead use whatever you have lying around. We’ve successfully started seeds in egg cartons, milk cartons, and cardboard trays. You can even fill empty eggshells with seed starter and plant seeds inside to start them that way. As long as your seeds have good soil, sunlight, and water, the process is quite forgiving.



Herbs and greens growing in the baking tray.

Lettuce growing in the clamshell greenhouse. We need to be thinned!

Because it actually took me a couple of weeks to get this post up, I can confirm that both types of mini-greenhouses worked and both sets of plants are doing great! In a future post, I will also talk about successfully transplanting the seedlings and caring for your plants during the growing season. For now, have fun and good luck starting your seeds.


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