Making soil blocks, which is the process of molding potting soil into cubes for the purpose of starting seeds, is an easy and efficient way to start your vegetable and flower seeds. It promotes vigorous root growth and healthier seedlings that won’t experience transplant shock when planted out into the garden. It also reduces plastic waste, because you don’t have to use any of those disposable plastic trays traditionally used for starting seeds. Soil blocking was first developed by Eliot Coleman, a pioneer in modern day organic growing. Be sure to scroll down to see our YouTube tutorial on how to make soil blocks and get our free potting mix recipe which you can use to make your soil blocks.

My experience…

I have been making soil blocks to start my own seeds in for several years now. It does take a little bit more time than just filling plastic cells with soil, but the results in healthier plants are more than worth it. The key to success with soil blocks is to use a growing medium that is the right consistency for making solid soil blocks. I have a tried and true soil block mix recipe that I will share with you. It’s made from four simple ingredients and contains all the right nutrition your seedlings will need to thrive. It is much cheaper than buying potting mix at your local hardware store, and is easy to mix up anytime I need to start some seeds. The best part is that it’s just the right consistency to make perfect soil blocks!

What are soil blocks?

As mentioned above, soil blocks are just potting soil that has been molded into blocks. There are different sizes of soil block makers that you can purchase and each of them has a small indentation in the middle of each block designed to fit the next size block. This makes it easy to pot up your seedlings into bigger blocks when it’s time.

Micro soil blocker – the micro soil blocker makes really small blocks which is nice for maximizing your seed starting space until your seedlings start to get big. You can put a lot of these little soil blocks into a tray which helps when you have a lot of seedlings to start on a limited amount of heat mat space, or if you don’t want to run a lot of grow lights while your seeds are just germinating. It doesn’t take long however before these little mini soil blocks will need to be “potted up” into bigger blocks
2” soil blocker – the 2” soil blocker makes 2-inch blocks. They have indentations in them so you can put your mini soil blocks with the tiny plants in them directly into the bigger blocks without disturbing the root systems at all. I usually just plant all of my seed directly into the 2” soil blocker. It saves me the time in potting plants up from the mini blocks to the 2” blocks. Most of the time I then just plant the 2” soil blocks directly out into the garden. I can fit 50 2” soil blocks in a regular 10” x 20” tray. These trays fit neatly onto my seed starting racks.
4” soil blocker – the large soil blocker is designed so that the 2” soil blocks will fit neatly into the indentation in the middle of the 4 inch soil blocks. This makes it easy to pot things planted in the 2” soil blocks up into the 4” soil blocks. I don’t use the 4” soil blocker very often, but they would work great if you wanted to have really big tomatoes when its time for transplanting.

Why Grow In Soil Blocks?

Healthier Plants. If you’ve ever purchased plants from a local nursery or greenhouse that have been grown in plastic containers, you will notice that they are very root bound. That is because the roots grow to the edge of the soil, and then continue to grow around and around in a circle in the plastic cell until they are all bound up with each other. The issue with this is that when you go to transplant them out into your garden, the plants will show signs of shock while their roots take time to figure out how to detangle themselves, quit circling and begin growing normal. When you grow in soil blocks, as the roots reach the edge of each block and find air, they stop growing. This actually air prunes the roots. This means they wait patiently until they are transplanted into more dirt before continuing to grow. When that happens they begin growing right away without any signs of transplant shock. This helps to thrive more quickly and produce fruit sooner.
Reduces plastic waste. You don’t need to buy anymore of those plastic cell trays for starting your own seeds. This saves you money on your seed starting supplies and reduces the impact on the environment.
Easy. It’s very simple and easy to make soil blocks. The key to succes is having the right consistency of moisture in your soil mixture. With a little practice, you’ll be able to make hundreds of soil blocks in a short amount of time.

Frequently Asked Questions

What is the best potting mix to use with soil blocks?

I always mix my own potting mix for soil blocks. It’s inexpensive, easy to mix up and is the perfect consistency for soil blocks. Here is a link to the free printable recipe.

How do you water seedlings in soil blocks?

The only way to water seedlings in soil blocks is by bottom watering them. I recommend making the soil blocks in a tray with holes in the bottom and then placing that tray into a shallow tray without holes in it. This makes it really easy to pour water into the base of the tray without making a mess and allows the roots to suck up just the amount of water that they need into the soil blocks. If you try to overheard water soil blocks, they can break apart.

How often do you water soil blocks?

When the soil blocks start drying out, add some water to the bottom tray. It’s important to keep them moist so the plants can grow quickly. I usually have to water mine ever 1-2 days.

Why are my soil blocks falling apart?

If your soil blocks are falling apart, your potting mix is too dry. Add some more water to it until you get a wetter mix.

Do you have to cover seeds in soil blocks?

It depends on the seed. Some seedlings like to be started in the dark, so they need to be covered with a bit of soil, and other seedlings like to be started in the light. Some smaller seeds like lettuce can just be dropped on the top of the soil block and allowed to germinate that way. Larger seeds like squash or cucumbers should be pushed down in the soil or covered with additional soil.

Learn more about my budget friendly DIY indoor seed starting setup here:

How do I know when to start my seeds indoors and how many seeds I need to start?

I use a free online app called Seedtime to show me when to start each kind of seeds based on my growing season.

Read more about how I plan and design our ½ acre market garden here.

Supplies You Will Need

Soil Blockers (I recommend getting the 2 inch soil blocker for sure, the others are optional)

Heavy duty propagation trays with drainage holes (these will last you for many years)

Heavy duty propagation trays without drainage holes (for bottom watering)

Soil-Blocking Mix Ingredients

Peat Moss – from local hardware store
Compost – you can use your own homemade compost or purchase from your local hardware store
Course Perlite
Fertilizer – This is my favorite fertilizer for this potting mix

How to make soil blocks

Mix up a batch of our potting mix in a large container.

2. Add water until the mixture is fairly wet. When you squeeze a handful of soil, you want a bit of water to squeeze out. I like to use warm water as it makes the soil warm which helps the seeds to germinate faster.

adding water and fertilizer to potting mix

3. Mix potting soil ingredients together and keep adding water until you get the right consistency. I find this easiest to do with my hands.

4. Press your soil blocker down into the soil and move it back and forth until all the cells in the soil blocker are filled. I like to pick it up and look in it to make sure they are full. You can also grab a handful of soil in the palm of your hand and push it into the cells to make sure they are packed nice and tight.

5. Scrape the soil blocker on the edge of your container to level off the bottom so your soil blocks will sit flat.

6. Place the soil blocker in the tray, and press down firmly on the top of the soil blocker. While pushing down, gently pull up on the handle to lift the sides of the soil blocker. Carefully let the handle down part way while gently pulling up on the whole soil blocker. This will loosen the soil from the soil blocker so it will release the blocks cleanly into the tray. See my video tutorial below for demonstration.

7. Repeat steps 2 – 5 until your tray is full of blocks. Place tray with blocks into shallow tray without holes. Place your seeds in the soil blocks as desired. Stack trays in a warm dark place until seeds germinate. Then put them on seed starting rack to grow. Bottom water every 1 to 2 days.

We wish you all the best in your seed starting adventures. It is so amazing to watch little tiny seeds sprout and grow into beautiful and healthy plants. If this tutorial was helpful to you, please comment below and give this printable tutorial a 5 star rating. Feel free to tag us in your soil blocking and seed starting pictures on instagram @wagonwheelhomestead21.