Gardening With Gardner: Seed Starting – The Materials

Gardening With Gardner: Seed Starting – The Materials

You have your seed calendar, the space to start in, and now it’s time to gather up what you’ll actually use to grow them! At a minimum, you’ll need some sort of container and some growing medium.


The standard tray used in greenhouses is what is called a “1020 tray.” The name is very logical – these trays measure 10” x 20”. You can get many kinds, from solid trays with no holes, to those with a few drainage holes, to mesh-bottomed trays (if you ever buy a “flat” of plants at a nursery, you’ve seen these). If you don’t want to purchase trays, you can also use whatever you have on hand – like the trays that meat comes on in the grocery store, a sturdy plastic tray like you might see in a cafeteria, or even the containers that salad greens come in.


You can purchase inserts that divide a tray into individual pots, or cells. The cells are what you can fill with soil and sow your seeds into. Some of these inserts are divided into “packs,” like when you purchase a 4-pack or 6-pack of annuals from a nursery. The standard inserts will fit into a 1020 tray, but there are many different size cells. You can find an insert that will divide a tray into 200 cells, where each opening is just under 1” across, or as large as 18 cells, where each is about 3.25” across. Feel free to reuse containers you have, too! Milk cartons or jugs, small paper cups, cardboard tubes from paper towels, newspaper pots, upcycled yogurt containers… I also save just about every pot I get from a garden center, unless I damage it.


When starting seeds, moisture levels are extremely important. You want to make sure the soil remains damp so the seed can sprout and develop properly. Creating the proper environment can be as simple as misting the soil regularly and placing plastic wrap over your tray until at least half of the seedlings have germinated, but you can also purchase a clear plastic dome that will perfectly fit a standard tray. The benefit to a dome is that the seedlings will have a little bit of room and won’t be in direct contact with the plastic and condensation as they sprout. If seedlings are too wet, they may suffer from “damping off,” a fungal disease that causes them to wither where the stem meets the soil. Some store-bought trays will come with a dome (especially from commonly available brands like Jiffy or Ferry-Morse). This is also a situation where those containers from salad greens come in handy. They are rectangular, so they make efficient use of space if you’re placing a few on a shelf; they are deep enough to either plant in directly or place a few 6-packs into; and they have lids to help with humidity! I used a few of these in the past, and just made some small drainage holes in the bottom, filled them about halfway with soil, and sowed seeds directly into them.


You can make your own mix, or you can purchase a seed starting mix. You may see products that say they are “soilless” and be a bit confused. How can you have “dirt” that doesn’t have “soil?” Soil, like we have outdoors in our gardens, contains things like microorganisms and may contain undesirable ones, as well as disease, fungi, or bacteria. Garden soil can also be heavy and may not drain well. A soilless mix, however, is more sterile, is lightweight, often has small, uniformly sized particles so that it’s easy for delicate roots to become established, and it drains well. It will often contain organic elements like coco coir or peat moss (peat moss is less sustainable than coir), mixed with perlite and vermiculite. Perlite provides good drainage and aeration, while vermiculite helps to retain water.


A seed will not need fertilizer right away. Each seed contains the energy that is needed for it to germinate. Once the roots appear and the teeny tiny little plant starts to grow, though, it may start to get hungry. If you have a seed starting mix that doesn’t contain any food for them, you can mix some compost in, or you can apply a liquid fertilizer after the seedlings have sprouted. When using fertilizers on seeds, it’s recommended to wait until “true leaves” have appeared (the first pair of leaves you seed are not true leaves). One of the most commonly used organic fertilizers for seedlings is a seaweed/fish fertilizer. Seaweed provides micronutrients while the fish elements provide macronutrients, resulting in happy plants. Make sure to follow the directions for seedlings – they will use a more diluted mixture than an established plant.

Soil Blocking

I couldn’t end without a mention of soil blocking! If you haven’t heard of it, you’re not alone, but it’s a practice that’s been around for decades. The technique was developed in Europe and has recently become more popular in the US. I first saw it on social media a little over a year ago. The process uses tools that form small cubes of soil, with shallow indentations where the seeds are placed. The result is efficient use of space, without the need for plastic cells. The “gaps” of air between the cubes also prevent the seedling roots from spiraling around and around, the way they might in a plastic cell. The smallest tool forms twenty ¾” cubes, with the next size up being a 2” cube. Large seeds can also be started in the 2” cubes, or smaller ones can be “bumped up” from the ¾” to the 2” as they grow. I will be trying this myself for the first time this year, but have heard that seedlings started in soil blocks can be stronger, less stressed when planted into the garden, and acclimate more quickly to being in the ground. There is a FREE YouTube workshop on Soil Blocking from Briana at Blossom and Branch Flower Farm in Colorado: Lisa Mason Ziegler of Gardeners Workshop Farm also has lots of free information on her website. She lists the mix she uses for soil blocking (a finer mix with more moisture is recommended). She also has instructions on how to use the soil blocker.

Find all of that here.

Seed Sources

Once you have your materials, the only thing left to do is sort your seeds! If you’re still looking to add to your collection, here are some seed sources (in addition to Burpee, Ferry Morse, American Seed, and other companies you’ll likely find in stores):

  • Eden Brothers
  • Park Seed
  • Johnny Seeds
  • Botanical Interests
  • The Page Seed Company
  • Baker Creek Heirloom Seeds
  • Gardener’s Workshop
  • Redemption Seeds
  • Floret Flowers
  • Seed Savers Exchange
  • Hudson Valley Seed Co.
  • Gurney’s
  • Harris Seed

Happy Sprouting!