I adore soil blocking for so many reasons. This post will discuss the benefits of soil blocking, why I love it personally, and what you need to get started at home.

In part two, I’ll talk more about the how-to’s and some tricks I’ve learned along the way. Feel free to comment below or send me an email with any questions!

First off, what is soil blocking? Simply put it’s creating little blocks of soil or seed starting mix in which to plant your seeds.

Initially, when I started growing flowers, I loved that soil blocking saved me so much space. Five years later, I’m even more thankful for that space saving aspect since I’m still starting seeds in my basement. Of course, I’m starting thousands more seeds than I was five years ago but with the addition of a few shelves, it’s still doable and that’s only possible because of soil blocks.

A typical plug tray that most growers use can hold anywhere from about 50 up to 288 seedlings. If I had to guess, I would say the 72 cell tray is probably the most popular, but with the 128 cell tray following behind. The number refers to the number of plants you can grow in said tray.

With my new soil blocker from Swift Blocker, I can grow 200 plants in soil blocks in the space that a plug tray grower could grow 72-128 plants (to be fair, as I mentioned there are plug trays that hold up to 288 cells/plants however those plugs are so tiny you really can’t use them for much other than lisianthus or they need to be potted up after a period of time anyway - I don’t have time for that!).

With my old, handy dandy 20 blocker, I could fit about 240 blocks in a tray. The only reason I switched is for time saving since I seed large quantities it just takes so long to do it 20 at a time when I could do 200 at a time.

For the avid home gardener, I highly recommend the 20 blocker! It will serve you very well!

The next reason I love soil blocking is because it uses much less plastic compared to traditional plug or cell trays. With plug trays, in addition to the tray itself, you need a bottom tray typically for support and to bottom water. That’s two trays for every batch of seedlings. There are heavy duty reusable options vs. the flimsy one-use trays but it’s still at least double the plastic.

With soil blocking, I am able to use just a single bottom tray and I use the same ones every single year and they’ll last for decades. I love my Bootstrap Farmer trays. I use the shallow solid bottom trays.

Reason #3: air pruning. Air pruning is when the roots of a plant are exposed to air and stop growing at the tip but instead branch off into more new and healthy roots. In contrast, inside a cell or pot, roots continue to grow lengthwise but because they are constricted inside the cell/pot they continue to grow and tangle and eventually become root bound. This can’t happen in a soil block as the edges are all exposed to air. This creates healthier roots and also reduces transplant shock when you get them into the ground.

This also creates healthier plants because as the roots branch and grow new ends, they are better able to take up nutrition and water.

What do you need for soil blocking?

A soil blocker (if you’re gardening at home you can make your own mold out of nearly anything, ice cube tray comes to mind but the possibilities are endless).
- If your interested in an actual blocker, I recommend the 20 block soil blocker. 20 seedlings fit in the palm of your hand at a size of 3/4” per block. For large seeds, like pumpkins or sunflowers, a larger block may be useful but I start 98% or more of my seeds with a 3/4” blocker.
A tray of some sort. For the first couple years, I re-used styrofoam meat trays and they honestly work extremely well. Of course, they come in various sizes so if you’re growing at home for your garden a small tray is perfect for 4 blocks. You can even separate the blocks if need be. For farmers or large gardens, you can use a shallow solid bottom 1020 tray.
Soil mix - I used to make my own mix composed of rock phosphate, sifted compost, sifted peat moss (can substitute coco coir), and green sand. I used the recipe from The Gardener’s Workshop and it worked beautifully for me for several years. She also sells a ready-to-use mix on her website. As my farm grew and I needed to start more and more seeds, I switched to a pre-made version as the time spent making and sifting the ingredients was getting to be too much. I now use Vermont Compost Fort Vee and I’m extremely happy with it.
Light source - I use simple LED shop lights. Seedlings do not need special grow lights as they are not inside long enough to be effected by the lumen level. At home, a super sunny window can do the trick too.
Heat mat - I use a germination chamber at this point but heat mats are when I started with. They are relatively inexpensive but easy to use. They come in various sizes so you can get a small one for home or larger ones for small farm operations.
- It’s important to get a heat mat thermostat otherwise it’s easy to cook your plants. They are cheap (can be found for less than <$20) and will save you a lot of hassle! Simply plug it in, stick the probe end into or between your soil blocks, and set the temp to the germination temperature on your seed packet.
Plastic wrap or dome - to keep moisture and heat at a steady level until germination. I no longer use either because of my germination chamber.

Remember, these items can be used over and over, year to year so it’s a small investment and commitment for growing healthy plants! And of course, I grow flowers but of course you can soil block for veggies too!

20 blocker on the left | Large 200 Swiftblocker on the right

Stay tuned for part 2!

Soil Blocking [Part 1]