Introduction to Soil Blocking

I set up in my basement (60 degrees F) to keep any mess where it belongs

Soil blocking, on first exposure, was both easier and more difficult that I expected. There is a certain technique to settling the soil solidly in the forms that I haven’t quite mastered, so my blocks are a bit uneven. On several occasions I had to remake a set of blocks.

There was also some tendency for the soil to stick in the form. I think the mix may have been too wet. Eliot Coleman’s book, The New Organic Grower (listed on my Resources page), says the mix is about 1 part water to 3 parts potting soil, but variable depending on the amount of moisture in the soil mix itself. I used 5 cups water to 18 cups soil; 4 cups didn’t seem wet enough. Even at about 4 3/4 cups of water I thought it a bit dry. I might have been wrong, I’ll try a different ratio next time, but a 1:3 would have been too much for the 512 Mix from Johnny’s Seeds.

Tools of the soil blocking trade

For mixing the soil and water, I just used a 3″ wide spatula I have handy in my basement. The plastic tray I used for mixing and as a foundation for block making is available through Johnny’s Seeds. The high back and low front make it very accessible as well as quite able to contain the soil. It’s useful to have a bucket of water at hand to dip the soil blocking tools into after each round of making blocks. That keeps the tool clean and less likely to stick.

I also used less potting mix than I anticipated. It took about a third of the prepared soil to host the 42 seeds I started today. I put the leftover in a plastic bag sealed with a twist-tie. I’ll add water and soil to it next week when I start a larger number of seedlings.

On the other hand, it’s probably essential to make too much soil since there has to be enough soil to completely fill the soil block forms. That means there will be some waste at the end. (Like the extra cookie dough scraps after you’ve made all the shaped cookies you can.)

Hand seeding with a simple metering tool

I purchased an inexpensive hand metering device thinking it would help me handle very small seeds, and I was not disappointed. It’s not the most efficient method, but a lot better than either trying to pick up tiny seeds with my stubby fingernails or wasting seeds by sowing multiples in one block.

The device works by placing the seeds in the round holder, choosing the size opening for the seed, then gently tapping the device until a seed exits through the hole and slides down the chute. Three small ridges at the end of the chute help prevent the seed from leaving before you want it to, and help prevent multiple seeds dropping into one block.

Artichoke, Eggplant, Sweet Peppers started on soil blocks

For the most part it was effective. Twice I missed my mark by tapping hard enough to move my positioning. In both cases I was able to save the mis-directed seed by picking it up with the end of the chute. I suspect that after I’ve used this device a few more times I’ll be fairly efficient with it.

The same goes for the block making tools. A bit more practice and I’ll have a smoother operation. Especially once I determine the optimum water-to-soil ratio for my soil block mix.

UPDATE: For my second round of planting, I made soil blocks drier – using just 4 cups water to 18 cups potting mix (still 512 Mix from Johnny’s Seeds). That worked much better. The soil did not stick to the block makers, which allowed me to move along very smoothly and quickly, and create more perfect blocks, too.