How to Make Soil Blocks: Tools and Recipes

Soil blocking is one of those seed-starting techniques that mystifies a lot of gardeners. Typically used by herb and flower gardeners, the technique has almost unlimited applications. It’s great for smaller seeds, and for any time you don’t want to disturb sensitive plant roots.

Making soil blocks isn’t hard, especially when you have a good soil block mix and soil blocker. You don’t absolutely need a seed blocker to start your seeds in soil blocks, though. There are DIY methods of soil blocking too!

You might wonder, what is soil blocking? And why would someone go to the trouble of using soil blocks in the first place? We talk about it all right here. 

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What Is Soil Blocking?

Soil blocking is a seed-starting technique that begins with making soil blocks. Seeds are planted in these blocks, which sprout and grow. Then, starts are planted directly in the garden when they’re mature enough, or planted in containers to mature longer before transplanting. 

Soil blocks have different compositions depending on the recipe and the gardener’s preferences. The result of planting seeds in soil blocks is healthier plants. Blocks allow seeds to develop roots with less threat of disturbance. 

Benefits

There are many benefits to growing seedlings in small blocks. Soil blocking prevents root-bound seedlings and transplant shock that occurs from starting plants in plastic containers without any sort of air pruning access. 

During blocking, your seedlings undergo the process of air pruning. They die back slightly when they grow to the edge of the block. Because the root’s tendrils are air-pruned from the sides, seedlings send out more growth to the base of the block. A good air prune results in stronger root systems, as root growth isn’t forced into a spiral that causes boundedness. 

Increased oxygen availability also helps your seedlings grow healthier foliage and absorb nutrients more easily.

One final obvious benefit is you’ll save so much space when using soil blocks. This goes for your indoor seedling space and your garden space. 

Which Plants to Start in Soil Blocks?

Herb gardeners and flower gardeners use soil blockers to grow plants with very tiny seeds that need a lot of heat and moisture to grow. If you’re growing plants that are prone to transplant shock, like zinnias, bee balm, and even radishes and carrots, soil blocks are a great way to get those going. 

Plants like tomatoes, ground cherry, and eggplant need a lot of heat to germinate. If you’re growing these in your spring garden and you want to get a head start on the season, but it’s too cold outside, planting in blocks is an excellent idea.

Another reason to incorporate soil blocks rather than starter trays is they don’t involve non-biodegradable materials. Plastic pots can be reused, but once you’re done with them, they can sit in a landfill for ages.  

The Best Soil Blocking Tools

Now, you might wonder, what are the soil-blocking products available in the world today? Let’s talk about that before we discuss how to use them!

Hand-Held Soil Blockers

These soil blockers are operated by hand, with no extra attachments. Most of the time an inch soil blocker makes mini soil blocks, and the two-inch soil blocker falls into the hand-held category. Many mini soil blockers do. They also are mostly oriented toward making 2 to 4 blocks at a time.  

The difference between one and two inch blocks lies in the plants you’re most likely to start in them. Two-inch blocks are best for vegetables, especially the nightshades and flowers we discussed above. One-inch blocks are best for fast-sprouting plants like beets and carrots. 

Smaller blocks dry out faster, so it may be best to start with something larger as you get used to the process. To use a hand-held blocker, you’ll develop your seed starting mix, block it up, and then use your hand to pull the release lever, which reveals your finished mini blocks.

Stand Soil Blockers

Instead of a solely hand-operated release lever, stand blockers have a long pole with a release at the top. It works in the same way a hand-release does, but stand blockers often contain more cells. 

That means you can make a lot more soil blocks at once – anywhere from 12 to 35 with just one release. Stand blockers are more ergonomic than hand-cranked blockers.

Pre-Made Soil Plugs

While they technically aren’t soil blocks, plugs are a great way to start seeds without starter pots too. They’re for people who love soil blocks but don’t have the soil mixture, blocker, or time to make soil blocks. They’re also excellent for indoor seed-starting ventures. 

Plugs are often sold inside kits. They’re used in hydroponics and are another way to prevent transplant shock in more sensitive plants. Just as you would with a soil block, you can plant your seeds within them and either pot up or plant directly in garden soil.  

Homemade Soil Blockers

If you want to save money and still use seed blocks, make your own! A toilet paper tube, clean soda cans, or even a sanitized push pop container allows you to seed start with DIY blocks. 

If you’re using an empty, sanitized soda can, cut the top and bottom of the can off (being careful not to cut your hands in the process). Cut the can down one side, and wrap it somewhat loosely around a wooden dowel about the size of a closet bar. You want the can to move smoothly around the dowel, acting as your release. 

Fix the ends with electrical tape, and move the dowel so the height of your soil blocks is left in the space at the end. Press in your soil mix, then put the end with the soil in it on a flat surface. You want your growing medium to be pressed enough so the water comes out the top. Then push the compacted mix out of the DIY blocker, and you have a single mini-block. 

If you are making blocks with kids, an aluminum can may be too sharp. In that case, a sectioned paper towel roll, or toilet paper roll works. One important thing to remember is to allow for more girth at the base of the block. Give it a flat bottom too, and it will stand more easily.

Related Supplies

When you soil block, you’re going to place your blocks in trays, or a larger container of some kind. Reused plastic containers work, and so do cookie sheets. Even the plastic lid leftover from a cake, or deli tray can serve as your tray.

The smoother the surface of your tray, the more balanced your soil blocks will be. An uneven tray can cause soil blocks to deform over time, and this may make them less stable.

Dibblers come with soil blockers, and sometimes they’re built into the blocker itself. These are inserted within the mold forming part of the blocker and make an indentation where you can place your growing seeds.

Keep a spray bottle handy to water your starting blocks with a fine mist, but if you’re bottom watering, you may not even need one. 

Another consideration is humidity. If you’re working with plastic trays or fiberglass trays, you may want to add some kind of dome over the top to ensure there’s enough humidity to support seed growth. Plastic wrap with holes punched in it works too.

A watering can that can slip between blocks to bottom water is necessary. A bin for combining your block mix is a great addition, as well as a soil sieve that removes any of the large chunks in compost and commercial potting mix.

Soil Blocking Mix Recipes

Before you develop your seed-starting mix, you want to determine how much you need. 

Many of the recipes base these amounts on the US bushel measurement, equating to just over 9 liquid gallons or about 2150 cubic inches. Most home gardeners won’t need more than a ½ bushel of starting mix. Those working on farms and large-scale growing operations may need multiple bushels.

Peat-Free Soil Block Recipe

Peat production practices have led some gardeners to look for alternatives they can include in their soil block recipes. Because peat is a nonrenewable resource that isn’t always effectively managed, many recipes substitute coco coir for peat.

Briana from Regenerative Gardening is a huge proponent of soil blocking and has lots of practice with her soil block maker. She has worked with various peat-free recipes and has extensively tested mineral and fertilizer additions. This is her recipe (and is our personal favorite):

Basic Soil Block Recipe

Our recipe here will cover what you need for a very simple seed-starting mix. If you want to work with more, scale up your ratio of ingredients by adding to that as needed. 

You absolutely need a basis for your mix. Some recipes include only sand for drainage and airflow, and compost for water retention, nutrients, and some slight acidity. Others add in peat moss or coconut coir, greensand, and mineral sources, like rock phosphate or azomite. 

With that in mind, we’ll start with a basic recipe and then include some variations. 

The most basic recipes and even the more complicated ones are great for making your own soil blocks, and you’ll have a perfectly adequate flat that works for starting seeds indoors. All the ingredients are included to assist in the germination process and support growth.  

How To Make Soil Blocks

Sift any implements as needed to remove large chunks. Pre-hydrate your peat or coir materials. Mix the ingredients together with two to three parts water in batches of one part at a time. Keep a little bit of excess soil on the side just in case you need to readjust after adding water.

Mix to a consistency that allows you to form a ball that mostly stays together and pours out water when you squeeze it. You will use this in your two-inch soil blocker or in your mini-blocker to make mini-blocks. 

Pile up the soil in your bin or on a rigid surface, and press the block down into the pile, shifting side to side to ensure it’s packed in. When you see mud emitting from the top of the blocker, pick it up from the soil, and level the base with a spatula. Using the release level, set your blocks into your cell trays by pulling them up at the same time. 

Leave some space between the sets of blocks to ensure there’s a good amount of airflow. Dip your blocker into warm water between blocking to clean it off.