I bought a new
toy tool for the garden this year, a set of soil block molds from Lee Valley Tools. They produce compressed cubes of potting soil that allow you to plant seeds without using pots.
This was appealing for three reasons: I hate cleaning the smaller seed pots that I use for starting some seeds; I can plant the soil blocks directly into the garden without disturbing the seedlings’ delicate roots; and the plants shouldn’t become root-bound, a condition where their roots grow around the inside of their pots and form a dense mat. The roots should just grow to the edges of the soil blocks and perhaps into the air, like last year’s kale seedlings in their peat pots. Unlike peat pots, there shouldn’t be a problem with the transplanted seedlings drying out due to the peat pot acting as a moisture wick.
The large mold on the upper left makes four cubes that are about 48 mm (almost 2 inches) on a side, while the small mold on the right makes twenty cubes that are about 18 mm (nearly 3/4 inch) on a side. In the middle, you can see a plastic cube insert that can be screwed into the large mold to make a space into which a smaller cube will fit; this is used if seedlings started in the small cubes need more space to grow. Additional inserts and their associated hardware are in the plastic bag.
The molds come with a recipe for making your own potting mix, but I used some commercially prepared mix that I already had. This might make my blocks crumble more easily. The instructions tell you to add enough water into the potting mix to make it the consistency of mortar, then to press the molds down into the mix to fill them. I found it was easier to fill the molds by forcing the mix into them with my hands; if you’re not willing to get your hands dirty, perhaps gardening isn’t for you! I set the filled mold in a pan, held the spring-loaded plunger in place, and pulled up on the handle that is attached to the body of the mold to release the soil cubes. This worked pretty well.
You can see the divot in each cube that provides a spot to plant a seed. I only needed three of the large cubes, so I removed one. It held together better than I expected. Even the large soil cubes look small when compared to the pots in which I plant my tomato seeds.
The molds cleaned up easily, only requiring some rinsing to remove all the potting mix.
The soil block molds are made in Britain and seem very sturdy. They should last a long time. However, they are rather expensive: I could buy enough peat pots to last me several years for the price of the set. On the other hand, the small blocks allow me to start many plants in a small space, which is especially useful with plants that don’t germinate well; those plants that do come up can be moved to the larger blocks as they grow.
Only time will tell how well I like these soil block molds. I’ll try planting a variety of seeds in them and see how well they grow and transplant.