Soil blocking is an innovative method for seed starting in an attempt to save resources while also protecting young, tender seedling roots. Gardeners can design their own tool to bring this practice into action keeping the costs to a minimum.
Soil blocking has been used for over 1,000 years in some parts of the world. The basics involve creating a soil consistency that can hold its shape allowing the seedlings to grow without being contained in a cell pack. This allows more oxygen to get to the roots promoting better growth. The roots will “air prune” themselves to stay in the dark soil rather than become exposed to the sunlight which prevents plants from becoming rootbound.
Begin your soil blocking experimentation by creating the proper soil mixture. You can purchase soil blocking mix online or make your own basic mix of three parts peat moss, two parts perlite, two parts garden soil and one part compost. The peat moss is an important ingredient because it binds all the materials together. You can also incorporate some fertilizer to the mix or add it later as you water the seedlings.
After your soil is thoroughly combined, add water until the mixture holds together when clumped into a ball. Three parts of the soil mixture with one part water should be adequate. It should not be so wet that it drips when you squeeze it, but it should be close. This is a wetter seed starting mix than most gardeners are used to, but it is necessary for establishing the blocks.
It’s time to pack your soil blocker. This is a tool that can be purchased online or made at home. For the DIY version you will need an empty soup can. You may choose to make a small soil blocker for starting smaller seeds and a larger soil blocker for the larger seeds. To make the small soil blocker, a small tomato paste can is a great size. Alternatively, you could use 2-inch cut sections of PVC pipe to make your soil blockers. For the can method, remove both ends of the can. Save one end of the can and screw it onto a 4- to 6-inch wooden rod. Use caution when handling the can lid as the edges will be sharp.
Firmly pack the empty can with the soil mixture. Push down to remove any air pockets and force the soil to compact and hold together. This is essential for your block to maintain its shape without support. Holding the wooden rod, push the can lid through one end of the can forcing the soil mixture to come out the other side and onto a tray. This is a soil block. Repeat the process with the sizes desired based on your seed starting needs.
Line up the soil blocks on a tray so the sides are touching. Growing soil blocks on a tray with a lip, such as an edged cookie sheet, will allow the water to collect and be absorbed into the blocks. Plant seeds according to package instructions but use care to not damage the edges of the soil blocks. Watering must be done from the bottom to avoid damage. When establishing soil blocks, the mix is very wet so the blocks will likely not need to be watered again for two to three days.
This simple project can make a big difference in the success of your garden. You can also benefit from the savings in materials.
Cynthia Domenghini is an instructor and coordinator for K-State’s horticultural therapy online certificate program.