DIY Soil Blocker: How To Make Soil Blocks For Seed Starting

(Image credit: Petra Richli)

If you enjoy starting seeds as your first project of late winter or early spring, it may be time to rethink how you do it. A soil blocking tool is a perfect way to efficiently grow healthier seedlings with less plastic waste. 

What is a Soil Block Maker? 

A soil blocking tool is a device that creates plugs of soil for starting seeds. Standard blockers create four 2 inch by 2 inch (5 x 5 cm.) plugs at a time. 

The 2 inch (5 cm.) blocks work well for most needs, but for tiny seeds that need a little more warmth as they germinate, you can find half-inch (1 cm.) seed blockers. You may also find some in other sizes, but these two are most common. 

To use a soil block maker, you pack it with your potting mix and then press the handle of the blocker to release the plugs into a tray or other container. 

Making a DIY Soil Blocker

You can also make your own soil blocker with throw-away items you have around the house or tool shed. An old soup can with both ends cut off or a piece of PVC pipe creates perfect cylindrical plugs. Use a dowel with a circle of plywood attached at the end to push the plug through. 

If you’re handy or crafty with tools, you can even make a multi-blocker out of several soup cans or pieces of PVC. 

Benefits of Using a Soil Blocker

If you are on the fence about using a soil blocking tool and starting your seeds this way, consider the benefits: 

  • A soil blocker creates a perfect little plug of soil that requires no container. 
  • You don’t have to waste plastic or find reusable containers from around the house to start your seeds when you use soil blocks. 
  • Plants benefit too. In standard containers, plants become rootbound. In a soil block, seedlings naturally air prune their roots. When they reach the edge of the block, they stop growing. This stimulates secondary root growth, which results in a more robust root system and healthier plant. 

Making Soil Block Mix

Most gardeners have their own magic mix, but this soil block recipe gives the best results when using this gardening tool: 

  • 3 parts peat moss
  • 2 parts garden soil
  • 2 parts perlite or sand
  • 1 part compost

You might also want to add about a quarter cup of lime and a half cup of fertilizer or bone meal per bushel of mix. The important part is the ratio of the main ingredients. Mix them together with water to create a moist mix that will hold its shape but not be soggy or dripping with water. This mix is ready to be blocked. 

Mary Ellen Ellis

Mary Ellen Ellis has been gardening for over 20 years. With degrees in Chemistry and Biology, Mary Ellen's specialties are flowers, native plants, and herbs.