5 P.M. INTERVIEW: UW-Extension Soil Blocks

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DURAND, Wis. (WEAU)— You are probably familiar with plastic trays that greenhouses use for starting plants, but soil blocks are different. They are literally a block of soil. The blocks are formed using special molds such as these for making ¾” blocks or 2-inch blocks. To make the blocks you need to have the right soil mix. Greenhouses or seed supply companies should be able to provide you with the right mix, or you can mix it yourself from recipes you can get on-line.

Besides having the right soil mix, you need to add enough warm water to the mix – until it is about the texture of oatmeal. This is critical for forming blocks that will stay together until the plant is ready to be put in the garden. To make the blocks you simply press the mold into the soil until it is full and packed hard. Then you push the blocks out onto your growing tray. Wetting the mold between batches helps the blocks to release cleanly.

The blocks are formed with a small divot for the seed. You can immediately plant the blocks, and since they are well water with warm water, they tend to germinate faster than traditional trays.

What are the advantages of soil blocks?
• The most obvious advantage is that there are no small trays to dispose of or try to store and reuse.
• Secondly, because the blocks are exposed on all sides, there is more oxygen for root development – and what is called “air pruning” - resulting in a strong root systems that is not tangled and root bound like we often see with plastic trays.
• Thirdly, the blocks tend to result in less disturbance of roots during transplanting so shock is reduced, and the plant is more quickly established once planted in the garden.
• Lastly, the blocks are useful for starting a lot of different plants, even those you might typically sow direct in the garden, like lettuce or other greens, or even more difficult plants such as corn or cucumbers. By giving these plants a head start they are more likely to out-compete weeds, get ahead of insect pressure, or be easier to adapt to no-till gardening.