LET’S TALK ABOUT plastic in the garden. Nursery pots and trays, plant markers, bagged goods and tarps, plastic netting, protective row-covers and even some tools — our green industry practically runs on plastic. And boy, does it accumulate — I stopped counting when I got to 100 4-inch plastic pots under my potting bench. Don’t even get me started on plant tags. With an already-overburdened waste stream, anything we can do to reduce plastic in our lives is a good thing.
What if we did away with pots altogether? Several gardeners I know swear by soil-blocking tools and techniques that do just that. I reached out to Jen Goff, a tool technician with Johnny’s Selected Seeds, and asked her to walk me through the perks of using a soil blocker, a sturdy metal tool that is used to form cubes of soil that you can seed directly into.
I confess, it looks a bit unnatural — I mean really, a free-standing cube of soil?
“They hold up better than you might think,” Goff assures me. “But there are some tricks to making quality soil blocks.”
1. Mix up an appropriate seedling medium, one with plenty of fibrous material, like peat, to increase moisture-holding capacity and create stability in the soil block until roots have a chance to fill in. You’ll find numerous seed-blocking soil recipes online. I asked Goff about substituting more sustainable coconut coir for peat. Turns out you’ll have better soil-blocking success with long fibers in your seedling mix; if you can source a fibrous coconut coir, give it a try.
2. Moisture is key; not working with a wet enough seedling mix is a common mistake that causes soil blocks to crumble prematurely. Goff recommends adding enough water until your seedling mix has the consistency of wet cement. “Others describe it as akin to chocolate fudge,” she says. So clearly, much wetter than we’re used to working with when planting seeds conventionally.
3. Well-compacted soil blocks hold up better as seedlings mature. Use a sturdy open tub to prepare seedling mix and prep soil blocks. Push the soil blocker straight down through a mound of moistened seedling mix until the tool hits the bottom of the tray; it might take a couple of presses to completely fill and firmly compact the mix within each chamber. Twist the soil blocker against the bottom of the seedling tray and lift; scrape the bottom of the tool to remove excess mix.
4. Transfer soil blocks to a tray that will support seedlings as they mature by pushing down on the plunger in the tool’s handle to release soil blocks; repurpose clean plastic or Styrofoam trays from packaged meat for an upcycle win. Sow seed into the dimple on the surface of each soil cube. No overhead watering, just gently irrigate seedlings as needed by adding water to the tray and allowing it to wick up to the roots.
In addition to reducing the use of plastic in the garden, soil-block-grown seedlings thrive. Seedlings grown in traditional plastic cells and six-pack trays have a smaller soil volume, and roots begin circling once they reach the container walls. “In soil blocks, roots will grow to the edge of the block, where they encounter a small air gap and pause until they are planted,” Goff says. No circling means roots are poised to establish quickly with less shock after transplanting.