Soil Blocks and Why We Don’t Use them For Our Plant Sale

Let’s start with what a soil block is.

The concept is really simple. It’s a BLOCK of soil.

The soil block tools I use are ¾” and 2” soil blocks. I call them the big blocks and the small blocks to simplify it even further.

The smaller tool creates 20 small blocks of 3/4” by ¾” by 3/4” which is very useful for smaller seeds like peppers, tomatoes, zinnias, snapdragons, and basil.

The larger tool creates 4 large blocks of 2” by 2” by 2” with a square maker at the top called a dibbler. When the dibblers are in, they create a perfect square for the ¾” blocks to fit inside, making them the perfect combination of tools for growing in small spaces. These larger blocks also easily fit larger seeds like pumpkins, sunflowers, squashes, cucumbers, and nasturtiums. These larger seeds would break apart the smaller blocks.

The process to make the soil blocks is pretty simple.

Get potting soil, wet it so water releases when you squeeze it really hard, and then smoosh the soil blocker into the soil. Yes, smoosh is our official term for it.

We use a concrete mixer pan and a burger flipper to assist with our soil blocking to mix and smoosh.

Once there is enough soil in the blocker we put the tool on a tray and squeeze the handle to release the blocks.

There are techniques, tips, and tricks that make this whole process simpler and if I was demonstrating I would happily share it all, but these are the basics.

The benefits of making soil blocks for us are the space savings and happy plants.

Let’s start with space savings.

In a standard 1020 tray (10” by 20”- this is a typical “flat” size).

This standard tray holds 300 small blocks or 50 big blocks.

In order to keep the shape of the blocks we bottom water. Pouring water on top of these blocks causes them to erode. We have two trays in use. One has holes and one doesn’t. Each of the pink trays has a mesh bottom. We lift the pink tray, add water to the solid (non-hole) bottom tray, and set it back down for the soil blocks to soak up the water, then we drain off the water after everyone has their share of moisture.

Most of our flowers are grown in the ¾” soil blocks. One shelf holds 4 trays, each tray holds 300 soil blocks – so I can grow 1200 plants on ONE shelf with one set of lights.

It’s pretty impressive especially since I grow our cut flowers at 6” spacing for most of our heat-loving zinnias, greenery, and flowers we use for dried arrangements. My 44-foot by 3-foot beds can each hold 528 plants with this 6” spacing. I can grow about 60 tomatoes or peppers in the same bed.

Bottom line? I can grow a LOT of plants in a small amount of space.

If we are using these IKEA cafeteria trays we simply add water to the tray, wait until every block looks dark brown, and pour off the water into a bucket.

This watering process takes a while, but it can be done easily in our basement grow space. Greenhouses and large plant nurseries can just take out the hose and spray their potted plants without concern about getting their floors wet.

The other benefit to growing in soil blocks is healthy plants.

In a soil block, the roots grow and grow and grow until they reach the edge and are “air pruned”. When roots reach air they stop growing, thus air pruning.

These basil plants were started in the ¾” blocks and were potted up into 2” soil blocks.

Can you see how healthy the leaves look AND how happy the roots are?

When a plant is in a pot the roots start circling the pot, it’s called “root bound”.

This method of growing plants ensures no plant is root bound. There are growers who have studied plants grown in soil blocks and plants grown in pots. Once in the garden, the plants in soil blocks seem to just take off growing and the plants from pots take about an extra week.

I like to think of plants as needing their roots to unwind before being able to grow successfully. Soil block plants can just GO!

So a few questions.

1) Can we grow full-sized garden-ready plants from soil blocks?

Yes! See examples of Tomato and Pepper below.

2) If soil blocks are so amazing, why do we not offer soil blocks in our seedling sale? I’m glad you asked!

In our first year of growing, we did soil blocks and we grew 3 varieties of peppers and 5 varieties of tomatoes… we didn’t have a full tray of any of the varieties so we had empty spaces in each tray, creating more trays.

More trays meant more watering, more grow lights, and more shelf space which meant more cost…because our time was the biggest factor in growing, we try to pay ourselves for the hours of seeding, tending, and watering.

We tried to label each of the plants. We damaged plants, some plants weren’t big enough for a tag, and it was extremely time-consuming.

After talking to several growers, we decided to use 2.5” pots.

YES, pots that cause root-bound, slower-growing plants.

Those kinds of pots.

We were able to label each pot as the plant was put in them AND we were able to mix and match trays without concern about what pepper or tomato we had in our hands.

To combat the root bound-ness I give the plants a little extra time in the small soil blocks and then pot them up with enough time to grow into the 2.5” pot soil, but not get too root bound.

Our first year (2022) with pots was frustrating, to say the least, but not because of the pots. 

We had plans for big thriving plants, we were prepared for potting up, and we couldn’t get our seeds to grow. Our soil wouldn’t stay moist long enough, and it took much longer for our seeds to sprout, delaying the whole situation.

In 2023 we are better prepared with a Michigan-based potting soil, and fish emulsion fertilizer (stinky but gives nutrients to the baby plants), and we are ready to take earlier actions to get those babies sprouting and thriving.

I’m hoping to be giving the peppers a haircut before they head to gardens around the metro Detroit area (psst Peppers love getting haircuts, they branch out and form extra stalks so it’s like getting 2 plants in one).

Speaking of extra plants – going to pots gave me the opportunity to give more than one plant in some situations like herbs and flowers.

Going back to the basil example. Instead of growing one basil in the 2” (larger) soil block I now grow the basil in the smaller block and add 5 blocks to each 2.5” pot. I’m happy to be able to give our home gardeners 5 basil plants to pull apart and set into their gardens instead of just one. It feels good to be as efficient with our pots as possible.

That’s the basics of soil blocking for Fence Post Flower Farm.

What questions do you have? Love it? Hate it? Want to try it out?

I’m considering offering workshops on soil blocking and I’d love to hear your thoughts!

Comment below or send me an email at

I love to chat garden!

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