This Soil Method Is the Secret to Healthier Plants This Spring, Gardeners Say

Soil blocking is a healthy way of starting plants from seed. To start soil blocking, you only need a simple compression tool and the correct soil mixture.

We consulted Lauren Craig, an expert in sustainable gardening, to help you learn about soil blocking, why it’s so beneficial, and how to do it.

What Is Soil Blocking?

Soil blocks are compressed blocks of soil that have no outer container. The soil blocks act as both the container and the growing media.

Soil blocks are created with a soil blocking tool that presses and molds the soil into 3/4-inch, 2-inch, or 4-inch blocks. 

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Soil Blocking Benefits

Soil blocking is considered healthier for the seedlings because their roots are less likely to become root-bound, Craig says. The roots will “air-prune” themselves. This results in healthier root systems.

• Stronger roots: With better access to oxygen, the plant’s roots grow stronger.
• Easy watering: Watering is simplified because you add water to the bottom tray. Water wicks upward, Craig says, which minimizes algae on the soil’s surface.
• No waste: Plastic plant trays are eliminated because soil blocks require no outer containers.
• Faster germination: By germinating in small soil blocks, the seeds are closer to the heat and germinate faster. 

How to Soil Block

Block soil either by hand or, more commonly, with a soil blocking tool, Craig says. 

You can create a limited number of soil blocks by forming soil balls one by one by hand. Though slow and laborious, it’s a good way to experiment with soil blocking.

A better option is to use a soil blocking tool. Four-cell soil blockers cost $15 to $25.

“Should you opt to use a soil blocking tool, you’ll pack the cells of the soil blocker with the moist soil mix as tight as you can,” Craig says. “Ideally, you’ve compacted the soil mixture enough to ensure no air pockets remain.”

Then, place the soil blocker in a tray, push the handle down, and release it to produce soil blocks. The soil blocker presses a dimple on top of the block that’s ready to receive seeds.

The Correct Soil for Soil Blocks

It’s critical to get the soil mixture right when soil blocking so the soil will stick together into blocks.

“The soil mixture is generally comprised of 50-percent peat moss or coconut coir, which helps the block hold its form and retain moisture,” Craig says.

Craig notes that a mixture of quality compost and topsoil make up the remaining ingredients, though some gardeners add other amendments and fertilizers to feed the plants as they grow.

Add enough warm water to the dry mixture until you’re able to stick the soil together by hand. If you can form a ball and it sticks together, it’s ready. The mixture should not be wet or muddy.

“You should be able to create a ball that sticks together and is able to be wrung out while still retaining moisture,” Craig says.

When to Soil Block

Start soil blocks in the spring or any time of the year that is appropriate to the seeds in the block.

It’s time to move the block when the seeds have sprouted and the roots reach the edges. Transfer the block into a larger block or plant the block in the ground.

Start heat lovers like tomatoes in the smallest block to speed up germination, Craig says.

“Once germinated, plant the smaller block into the larger block, ensuring there’s no root disruption during the transplant,” Craig says.

Soil Blocking Tips

Refine your soil blocking techniques with these tips from Craig:

• Be patient, as it can take a while to fine-tune the process. 
• If the blocks don’t hold together, put the mixture back in with the rest and add a bit more water. Then, try again.
• Keep some dry mix on hand in case you add too much water. 
• Rinse the soil blocking tool after each use for tidier blocks.