Using Soil Block Makers

About Soil Blocks

Soil blocks are simply blocks of soil formed by tools called soil block makers, that are used to plant seeds indoors or in a greenhouse.

Commercially available soil block makers come in a series of sizes. At Mayetta Farms, we have three different soil block makers. Our smallest one is 3/4″, our next size up is 2″, and our largest is 4″. Each block maker creates a divot in the soil block it makes. The divot on the 3/4″ block maker, is just big enough to plant a seed. However, the divot in the 2″ block maker is a 3/4″ cube shaped divot – just the right size and shape for transplanting your 3/4″ blocks into, once the seedlings start to outgrow them. As you might have guessed, the divot in the 4″ block is a 2″ cube shaped divot – just the right size and shape for transplanting your 2″ blocks into. This process is called “potting up.”

That said, not all seeds are treated the same. If you are starting lettuce seedlings indoors, you may only use the 3/4″ block and plant that directly into your garden bed. Some larger crops grow so fast that I skip the 3/4″ block altogether and start them in 2″ blocks. Many crops are transplanted into our garden beds in 2″ blocks, and never make it to 4″ blocks. However, crops like tomatoes make the 4″ blocks necessary, because we like to get them started as early as possible inside, to get a head start on the season.

How to Use

  • Add water to your soil block mix. After a bit of practice, you will get a feel for how much water to use. You want the soil to be moist enough to hold together without crumbling, but not so moist that it becomes a mush.
  • Fill the soil block maker with the moistened soil, making sure that it is packed in tightly. If you don’t pack enough soil into the block maker, your blocks won’t be properly formed.
  • Release the soil blocks onto your germination tray.
  • Sow and cover your seeds with however much soil the seed packet recommends.
  • Carefully water the tops of the blocks. We recommend using a gentle mist setting on a spray bottle, to avoid displacing seeds.
  • Put plastic over the top to keep in the humidity.
  • Once you see roots emerging from the soil block, it is time to either place your smaller soil block into the next largest size block, or transplant it into your garden bed.

Pros and Cons of Soil Blocks


  • Soil blocks do not require any plastic. You set the blocks on germination trays. Some gardeners opt to make their own germination trays from wood for better durability, and to avoid plastic altogether. However, even if you use plastic germination trays, as I do, those kinds of trays last many years, unlike the flimsy plastic trays with cells, which are spent after a season or two.
  • Air pruning. When the roots grow to the edge of the soil block and hit air, they simply stop growing and wait for more soil. That way, when you put them in the ground they are ready to start growing in their new home. Conversely, when you grow in pots, you may have noticed that the roots wrap around the pot. This is called being “root bound” and it increases the risk of transplant failure.


  • Making soil blocks is very time consuming, and time is money on a farm!
  • Soil blocks are also quite messy. Ideally, you would have a greenhouse for this task, but they can be made inside, if you work on an easily cleaned surface.

Whatever method you choose, happy planting!

-Mayetta Farms

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