Soil Blocking: Tried and True Seed Starting Tech

Soil blocking is a seed-starting technique beloved by flower gardeners. Learn to make your own soil blocks in this detailed how-to guide!

Soil blocker and soil blocks

Contents

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 that you don’t want to disturb sensitive plant roots growing in early phases. 

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? You may also wonder about the best soil block recipe to use. We are talking about all of these things right here. 

So let’s discuss soil blocking in all its applications!

Epic Products For Soil Blocking:

What Is Soil Blocking?

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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 outplanting. 

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 in a situation with less threat of disturbance. 

Benefits of Soil Blocking

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. 

Because the root’s tendrils are air pruned from the sides, seedlings send out more growth to the base of the block. Many times, in the off-season, you may find yourself cleaning both the container you’ve started your seedlings in, and you just won’t have to do this with blocks.

During blocking, your seedlings undergo the process of air pruning, as they die back slightly when they grow to the edge 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 very obvious benefit is you’ll save so much space when you soil block. This goes for your indoor seedling space and your garden space. 

When To Start Plants in Soil Blocks

As I mentioned previously, 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, painting 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.  

Types of Soil Blockers

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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 the Inch soil blocker which makes mini soil blocks, and the two-inch soil blocker fall 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 1 and 2 inch blocks lies in the plants you’re most likely to start in them. 2 inch blocks are best for vegetables, especially the nightshades and flowers we discussed above. 1 inch blocks or ¾ inch blockers are best for fast-sprouting plants like beets and carrots. Our Ladbrooke Mini-5 soil blocker is 1.5 inches, which sits right in the middle of the large and small sizes and provides a good all-around size.

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.

A single, formed soil block
A single, formed soil block.

Stand Soil Blockers

In contrast to mini blockers, you have stand 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. This is a great feature, because making a  lot of soil blocks at once puts stress on the back.  

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 – like the EZ Clone Low Pro Aeroponic System. 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 up-pot or plant directly in garden soil.  

While their maintenance is slightly different from blocks, they are just as effective. 

Homemade Soil Blockers

Let’s face it. Soil blockers are great, but may not be an option for everyone. If you want to save money and still use seed blocks, make your own! Using a toilet paper tube, clean soda cans, or even a sanitized push pop container are ways 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 that’s about the size of a closet bar. You want the can to be able to move smoothly around the dowel, acting as your release. 

Affix 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.

Tray of soil blocks
Tray of soil blocks.

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.

Something to consider is that 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. We prefer our reusable, long-lasting fiberglass soil blocking tray, but any smooth surface without indentations or grooves can do in a pinch.

If you’re using a wood block or polycarbonate sheet, remember that including wooden sides or putting polycarbonate end walls on the sides will help you bottom water. Whatever you use, ensure it can handle the weight of your blocks before you plant your seeds.  

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 affix 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 in is a great addition, as well as a soil sieve that removes any of the large chunks in compost and commercial potting mix. A spatula or wide putty knife for mixing and leveling off your blocks helps too!

How To Make and Use Soil Blocks

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This is the section of the piece where we discuss soil block-making. We’ll start by looking at different soil 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.

Blossom and Branch 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, or they’ll use alternatives like PittMoss, which makes a peat substitute out of recycled paper.

Briana from Regenerative Gardening, the newest creator on our video team and the owner of Blossom and Branch Farm, 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):

  • 4 parts Coco Loco potting soil (from Fox Farm), sifted to remove chunks
  • 1 ½ parts coconut coir (if buying in blocks, rehydrate with water before measuring)
  • ½ part greensand (mineral sediment)
  • 1 scoop granular mycorrhizae (there are many brands of mycorrhizal additives available, or you can use an organic fertilizer with mycorrhizal additives like Espoma Bio-Tone)
  • A dash of cinnamon to lower the risk of algae or mold (optional)

If you do not have coco coir, substitute it with the following:

  • Leaf mulch or leaf mold, either straight from the garden or processed in a composter like the Lomi compost system
  • PittMoss, a recycled paper products replacement for peat moss

While other potting blends such as Fox Farm’s Strawberry Fields are viable to replace the Coco Loco, they include peat moss. If you want to keep your soil blocker recipe peat moss-free, use the recipe above. Briana has tested it over a long period, and it’s a highly effective mix!

Basic Soil Block Recipe

Our recipe here will cover what you need for a very simplistic 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 very basic recipe and then include some variations. 

The basic recipe that we use for seed starting includes the following:

  • 1/3 moisture retention ingredients,
  • 1/3 drainage ingredients,
  • 1/3 filler compost.

As these components can vary depending on what you have on hand, an example of this potting mix might include: 

  • 1 part of coconut coir, peat moss, or peat alternative
  • 1 part perlite, pumice, or sand,
  • 1 part sifted compost – this can be plant-based composts, composted manures, or worm castings, although the finished seed starter should not contain more than 1/5th worm castings due to their moisture retention capabilities,
  • A light sprinkling of a mineral additive such as greensand, azomite, or rock phosphate.

The most basic recipe 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

Underside of a soil blocker showing the dibber
Underside of a soil blocker showing the dibber.

Sift any implements as needed to remove large chunks. Pre-hydrate your peat or coir materials. Mix the ingredients together with 2 to 3 parts water in batches of 1 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 2-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 your spatula. Using the release level, set your blocks into your cell trays by pulling 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 and remove any detritus. Now that you know how, you can start most seeds in your two inch blocks, small seeds, or even more seeds than you have in the past! 

Frequently Asked Questions

Soil blocker and soil blocks
Soil blocker and soil blocks.

Q: How do you make homemade soil blockers?

A: See the DIY recipe above! It’s not hard to make your own.

Q: Are soil blocks worth it?

A: Absolutely. Next to our Epic Cells, soil blocks are the best way to promote healthy roots. 

Q: Can I use potting soil for soil blocking?

A: Definitely. If you have a good mix nearby, use that!

Q: Which soil blocker should I get?

A: Of course, we have a really good one in our store. Those new to blocking will do best starting with at least a 2 inch blocker, as there’s more leeway with a larger one. 

Q: How often do you water soil blocks?

A: Water them to keep them moist. Smaller blocks may require two waterings per day. 

Q: Why use a soil blocker?

A: Blocking helps you waste less seed, promote healthier growth, and save space. 

Q: Can I make soil blocks ahead of time?

A: You want to make them right before planting your seeds. 

Q: What do you add to soil to keep it loose?

A: Any organic matter will help aerate the soil and provide pockets for water retention.

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Three white plastic trays sit on a windowsill, filled with dark, moist soil. Sprouts of various heights and thickness carpet the soil, their leaves a vibrant shade of green. A few delicate stems stretch towards the window, bathed in the soft glow of the morning sun.

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