The Dirt on Soil Blocking

Have you’ve ever looked at your pile of plastic seed trays and wondered why you’re using so much plastic to start your seeds? Or perhaps you’re tired of struggling to get your seedlings out of the tray and put them in the garden. If this sounds like you, you may want to consider soil blocking.

I discovered soil blocking in the past few years and have been slowly moving my entire seed starting operation over to soil blocking instead of using traditional seed starting trays. Not only do I appreciate the decrease in practice but I find a bit more upfront work makes it easier in the end. In this article I’ll go into the details of how to soil block from start to finish including the supplies and equipment you need, how to create you blocks, and how to plant them out in the garden all based on my first hand experience.

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Why Soil Block

If you’re already considering soil blocking, you likely already know some of the benefits such as reduced use of plastic. But there are many other benefits to using the soil blocking method.

Improved root development: Soil blocks encourage roots to grow more naturally because they air prune rather than circling around the edges of a container. This promotes healthier root systems and can lead to stronger, more resilient plants. In a normal cell tray, when the roots hit the edge of the cell, they circle back. In a soil block, the roots will meet the air and become pruned.

In addition, the open structure of soil blocks promotes better aeration of the root zone, which can prevent issues such as waterlogging and root rot. This is especially important for plants that are sensitive to overwatering.

Reduced transplant shock: Since seedlings can be planted directly into the soil without disturbing their roots, they are less likely to experience transplant shock. This can result in faster growth and better establishment in the garden. This is my favorite benefit of soil blocking as I can quickly plant a tray of soil blocks.

Space efficiency: Soil blocks take up less space than traditional containers because they can be closely packed together without the risk of root entanglement. This makes them ideal for small-scale or urban gardening where space is limited. This assumed you will be using one of the small soil blockers.

Cost-effective: Soil blocking can be cost-effective because it eliminates the need for plastic pots or trays. Once you have a soil blocker tool, you can continue using it for multiple seasons without having to purchase new containers. While this is often listed as a benefit, you likely won’t see a huge cost savings until a few years into the system.

Environmentally friendly: By reducing the use of plastic pots and trays, soil blocking helps to minimize plastic waste. Additionally, since soil blocks are made from natural materials, they can be composted after use, further reducing environmental impact.

Customizable soil mix: When making soil blocks, you have control over the composition of the soil mix, allowing you to tailor it to the specific needs of your plants. This can be especially beneficial for starting seeds or growing seedlings that have particular soil requirements.

Soil Blocking Equipment

The biggest obstacle to overcome when you start soil blocking is collecting the supplies you need. Luckily soil blockers are available in many places. Below if everything you need to get started.

Soil Blockers

In general, soil blocks come in 3 sizes. The sizes refer to the size of each block created. There are 3/4 inch, 1.5 inch, and 2 inch soil blocks. When I first started soil blocking I started with the 2 inch block. While this block is generally great and provides excellent soil for your seedlings, 2 inch blocks take up a lot of of space. Eventually I’ve move to starting most of my seeds with the 3/4 in block. It’s also possible to transplant your 3/4 inch seedlings into 2 inch soil blocks if you aren’t ready to plant them outside.

You can sometimes find soil blockers at your local garden center or order them online.

Soil Blocking Recipe

You can’t just use seed starting mix for soil blocking as your blocks will fall apart. The best method is to create you own soil blocking recipe. This is sometimes the biggest obstacle for people as it takes a bit more work to get started. I’ve found that while it takes longer to source the ingredients for the soil blocking mix you can buy a lot at once and have it for a year or two.

The main difference is that you will need something that helps to bind the soil together so this blocks don’t simply fall apart in the tray. The most common ingredients to bind the blocks in coconut coir (sustainable) and peat moss (not sustainable). You can find many recipes online and we are constantly tweaking our own recipe for the best results.

Here are the ingredients I use for my soil blocking recipe:

  • 3 Buckets of Coconut Coir or Peat Moss
  • 1/2 cup Lime
  • 2 buckets perlite
  • 2 buckets fertilizer – I made my own by mixing bloodmeal, colloidal phosphate
  • 1 bucket garden soil
  • 2 buckets of compost

Mix your soil thoroughly and water before using. Many people prefer to sift their soil blocking mix and you may want to do this if you have a lot of debris in your mixture.

You can also find soil blocking recipes at:

Trays and Domes

You still need to put your soil blocks into some type of tray. The best trays will have a dome to control the humidity. Since I’ve already been using trays for a number of years, I simply used what I had. Many people also use trays they have left over from food or other take out. The best trays will have some type of groove in the bottom to make it easier to water.

Soil Sifter

A soil sifter is somewhat optional. This allows you to sift out any large debris that gets into the soil mix. You can find a number of options online or make your own with wire. Here are some sifters that work well.

Bucket, Tupperware or Wheelbarrow

Finally, you will need somewhere to mix your soil. You can mix the soil blocking recipe together with your hands or a shovel. I keep a tupperware bin with my soil starting mix so that I can easily put it aside and have it ready when I want to use it again.

Step by Step Guide to Soil Blocking

Using Soil blocks is very similar to growing seeds in seed trays with a few specific difference (mostly around watering). Below I’ll walk you through how to create, plant, germinate, and care for your soil blocks.

Create your Soil Blocks

The first step is to create your soil blocks.

Start by mixing up your soil block recipe. I like to use a rubber tub or wheel barrow to mix my soil together. Add enough water so that the soil clumps together when you grab a handful but doesn’t drip everywhere.

Once you’re soil mixture is created, I like to press my soil blocker into the soil and scoop it up so I get as much soil as possible into the squares. Use your hand to press the rest of the soil into the block.

Turn your soil blocker over in the tray and press down. I find it works best not to release the blocked until you’ve put some pressure down on the soil. Pull up and leave your soil block in the tray. We’ve found about 98% of the time we get a good block. Once in a while I’ll need to redo the block. This usually has to go with a lack of moisture in the soil.

Planting, Germinating, and Caring for your Seed Blocks

Once you’ve create a full tray of soil blocks. You want to plan a seed in each soil block just as you would in a cell tray. Some soil blocks with naturally have an indentation to plan your seeds. I like to place my seeds in this hole and cover with loose soil. Make sure to read your seed pack as some seeds need light and don’t do well when covered.

Once you’re seeds are in every block in your tray, cover them with a humidity dome and you want to find a warm place to germinate your seeds. You can use a heat mat, or place them in a warm place in your home. I like to add just a little bit of water into the bottom of the tray (do not pour water directly on your soil blocks or they will fall apart.

Check your seed blocks every few days for germination. Once about 50% of your tray is germinated, remove the dome and place under grow lights. The top of the seedlings should be just a few inches below the light. Keep your lights on for about 16 hours/day.

How to Water Soil Blocks

Check your soil blocks everyday and water before they dry out. To water your soil blocks, pour water directly into the tray. The soil blocks will wick the water up into the block. This help the soil blocks keep their shape. I’ve found soil blocks are a bit more dense compared to seed tray soil and don’t dry out that quickly – especially the larger blocks.

soil blocks ready to plant outside
Soil Blocking – planting your seedlings outside

Planting your Soil Blocks Outside

I love growing seedlings in soil blocks, but the best part is when it comes to planting the soil blocks outdoors in the garden. Instead of trying to pry each seedling out of seed tray, you simple pick up a seed block and plant it in the hole. This is easier, faster and also has less shock to the plant.

Once you’ve planted each block in the garden, water immediately and care for your seedling like you would any other plant.

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