How to Make Soil Blocks

In this post and video, I show you what's going on in my greenhouse as well as show you how to use my new favorite tool for growing in the greenhouse: soil blocks!

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The Spring Greenhouse

I recently shared a video that toured my heated greenhouse. Take a look over here. There wasn't too much going on at that point. Now, just a short time later, I've started a bunch of seeds.

I have started brassicas, including broccoli, cauliflower and cabbage. There are also beets and lots of flowers and herbs.

I finally have some tomatoes that are taking off in my 5-gallon buckets. Normally, I would get my first tomato harvest in July. I'm hoping this year I can start a little sooner with these greenhouse tomatoes.

If you're looking for seeds, check out Baker Creek Heirloom Seeds or Ferry Morse.

Soil Blocks

I recently read Eliot Coleman's book The New Organic Grower. He talks about how he starts all his seeds with soil blocks. I had previously heard about soil blocks, but I just wasn't sold on them. I always used plastic containers or peat pots. After reading Eliot Coleman's book and doing some more research about soil blocks, I decided I had to take the plunge and try them this year.

Soil blocks seem like a good way to conserve, keep plastic out of landfills and just use what you really need. Soil blocks are better for seedlings' roots and overall health.

I bought three different soil block maker sizes. I bought the mini, which is ¾". This one makes 20 small blocks at one time. Then, I have the 2" maker which makes four blocks at a time. There are other models that make more blocks at once. Finally, I have the 4" maker. This is the largest blocker I've seen. It's good for putting plants into their final spot before transplant. There is also a 1 ½" maker that you can buy.

Each soil block maker has a small indentation on the top where you place the seeds. The 2 inch block maker has pins on the bottom that can be switched out to accommodate different sized seeds. It also has a pin that is a square the exact size of the ¾" mini blocker, so that you can transplant seedlings as they germinate.

The four inch block maker has an indentation for the 2 inch blocks to be transplanted into as well.

The Soil Mix

Some people use regular potting soil to make soil blocks. I might try to use a seed starting mix to see how that works out. Eliot Coleman recommends a different mixture. There are a lot of different recipes for soil block mixes available online. I've been using a mix which is a combination of Eliot Coleman's recipe and a recipe I found online.

The soil mix recipe I am using is:

One part compost (learn how to make your own compost here)

Four parts peat moss

A little greensand

A little rock phosphate

Add water until optimal consistency is achieved

Making the Soil Mix

When making soil mix, use a large tub to mix it all up. You can make any amount at a time. Each "part" of the recipe could be a five gallon bucket if you are making a large batch. Or, it could be a measuring cup for a small batch. I use a 6 cup plastic container.

Ingredients

Compost

You can use compost that you have made or buy something from the store. I had some store bought compost because I didn't plan ahead, and when I was ready to make the soil blocks, all of my compost was frozen! I bought a couple of bags of organic compost from the nursery. Screen your compost on some hardware cloth to get out any bark or other large chunks.

Peat Moss

Some people don't like to use peat moss due to the harvesting and sustainability issues. This is something you should definitely research if you are concerned about it. Just make sure that you are getting peat from somewhere that is harvesting responsibly.

Greensand

Greensand is an organic fertilizer mined from ocean deposits. It is high in minerals. If you don't have this, you could use an all-purpose organic fertilizer or skip it altogether. The compost will naturally be adding some nutrition to the soil.

Rock Phospate

Rock phosphate is another organic fertilizer that is high in phosphorous. This is another one that you could probably skip or substitute an all-purpose organic fertilizer.

Process

Add all dry ingredients to your large tub. Mix them together. Then add water. I use about 2 parts of water for my mix. It's really important to use your judgement and add water until it feels like the right consistency for you.

Stir up all the ingredients with the water. You don't want your mixture too dry; otherwise, your blocks will fall apart. You also don't want it too wet. Getting the right amount of water has been my biggest struggle with soil blocks. Add water a little at a time to get the right consistency.

Making Soil Blocks

Have some kind of tray available for your soil blocks as you are making them. I use 1020 plastic trays, but you can use anything that is convenient for you to keep your seedlings in. Just make sure you can water your seedlings and move them around as needed.

Put the soil blocker into the soil mix and press down while rotating back and forth. Wipe off any excess soil mix. I like to push the soil mix in with my hands to make sure that each block is full.

Put the soil blocker into the tray, push down and release the soil blocks from the blocker.

After making each soil block, dip the soil blocker into water to rinse it off.

Planting Seeds in Soil Blocks

Pour seeds into your hand or onto a paper plate.

Use a wooden skewer, toothpick or pencil tip that has been moistened to grab seeds one by one.

Place each seed into its own soil block.

Once in the block, you can cover the seeds with a little bit of soil. Use only one seed per block to minimize waste.

To keep the seeds moist, use a spray bottle to mist them gently. Water a couple of times a day. The small blocks dry out quickly. You can put a plastic cover or plastic wrap over your seed trays to keep moisture in. Make sure to remove once a few seeds have germinated.