At Liberty High School Greenhouse we have been using a method to start seeds which is worth considering. We purchased two new tools called “soil blockers” which allow you to cut multiple small squares of soil. The size of the soil blocks you make using the tool is crucial, being 1.5” x 1.5” by 2”. That size of soil block is most efficient for starting seeds. We decided to start our seeds using soil blockers rather than plastic seed containers for multiple reasons.
We found the process to be more sustainable, there was less transplant shock, they use space more efficiently, and are easier for the smaller students to transplant. A nice bonus is that we no longer have to wash used plastic containers in bleach solution between plantings. Aside from the initial cost of the two soil blockers, it was not an expensive transition.

Seed blocker. photos by Sheila Clyatt

To make soil blocks you will need the “medium” or seed starting mix, a large inexpensive mixing pan and and some flats to put the blocks into.

It sounds more complicated than it is, so let's start at the beginning with the soil medium. You can buy pre-packaged seed mix or make your own like we do. Here are the simple ingredients in our mixture:

1 bucket peat moss
½ bucket sterilized compost
1/2 bucket of perlite
1 cup blood meal

Mix the ingredients in a mixing tub. We use a plastic cement mixing tub. Add enough water so the soil becomes wet enough to hold together but not runny. 

Now “load” the blocker by pushing your tool into the tub and filling the cavities with soil. Unload the blocker by pushing down the handle over your plastic flat and the little squares will be formed. Repeat till tray is full. 

Each square of soil has a little indent on the top to place a seed and if you want to cover the seed you can use perlite or just leave it exposed like we do. 

We place the trays on heating pads in the greenhouse and set the mister to come on twice a day for 5 minutes. This is enough to keep the blocks from drying out but not enough to drown them. If someone is on site, it is preferable for them to just fill the flats with water once a day. Seedings prefer bottom watering rather than overhead. To achieve this without being on-sight daily we are exploring the use of a capillary mat attached to a side water reservoir. It's fun to see what improves the overall outcome of seed production.