Soil Blocks: What are They and Should You Make Some?
Similar to basically any other facet of our lives, trends come and go in gardening as well. This is evident in the growing interest people have in soil blocks over the last couple of years. Even though it’s actually nothing new, I can see it turning into the next hot trend!
A soil block is produced using a moisture-retaining potting mix, water, seed, and a mold often called a blocker. The practice of soil-blocking is gaining popularity as it is considered a more eco-friendly way to start seeds compared to using regular seedling trays. The benefits of soil blocks include air-pruning and reduced transplant shock.
Without further ado, let’s get digging into it!
What is Soil Blocking?
As it turns out, soil blocking is a practice with origins that can be traced back to thousands of years ago somewhere in Central America!
From the name itself, you already probably have an idea of what the process is like and what a soil block is. Nevertheless, let me paint the picture for you.
Soil blocks are made by lightly compressing soil into a mold to serve as both the growing media and “container” for starting seeds. Molds are typically designed to leave a divot at the center—perfect for seeding.
Don’t fret though! Soil blockers are not as expensive as you might think. In fact, you can get pretty good ones under 20 bucks like this one from Amazon. It’s perfect for small gardens.
You can also find a lot of package deals that include multiple sizes of molds which is ideal for no-fuss transplanting. Those blockers (here on Amazon) are often made of metal as well. Meaning, they’re sturdy and reusable.
If you’re good with crafting, you can also try your hand at making your own soil blockers. I’ve seen people make it with old tin cans and some large screws and bolts.
Others have also fashioned vintage metal ice cube trays and brownie trays with built-in dividers (so everybody gets crispy edges with each slice) into soil block molds.
A Quick Tutorial on How to Make Soil Blocks
Look, I know that trying out new things can be overwhelming, especially when time, money, and effort are necessary to pull things off.
This is also true for trying out new gardening methods. Honestly, this is why I thought to write out a short but detailed article on the topic—to help other home gardeners.
As with regular gardening, start off by mixing your potting mix so that all the materials are evenly distributed and incorporated. Then, slowly but surely add warm water to it.
Pro Tip: Add 1 part water for every 3 parts of your potting mix. Though this much water may look like too much, it’s necessary for the soil block to stay in shape even after being unmolded.
From there, simply fill up your mold by pushing it into your container filled with the potting mix. Twist it around and repeat doing so to ensure that your blocks are fully packed—they shouldn’t crumble easily.
Release your soil blocks onto any shallow container, you can use your existing flat trays for this. Even old plastic food containers from takeouts will do just fine.
Just continue blocking until you have enough for all of the seeds you’re planning to plant!
What is the Best Potting Recipe for Soil Blocks?
Regular starting and potting mixes typically don’t retain as much water as necessary for soil blocks to retain their shape.
A lot of recipes will recommend mixes containing up to 50% peat moss or coco coir. Sterilized compost and vermicast are also popular additions for making soil blocks, and so are perlite and sand for good drainage.
| Recipe 1 | Recipe 2 | Recipe 3 | Recipe 4 |
| 1 part coco coir 1 part vermiculite 1 part compost | 1 part peat moss 1/2 part compost 1/2 part perlite some blood meal | 1 part peat moss 1 part compost 1/3 part perlite some granular fertilizer | 1 1/2 part coco coir 1 part perlite 1 part compost some garden lime |
Otherwise, you can just buy ready-to-use special starting mixes like this one from Johnny’s Selected Seeds.
7 Advantages of Using Soil Blocks
1. Air-Pruning
The growing medium of a soil block isn’t blocked off by the walls of a seedling tray or nursery pot. Once the roots grow past the block, it pretty much cuts itself off and encourages better overall rooting.
In other words, you can reap the benefits of air-pruning at a very early stage of your plants’ development. This also prevents plants from becoming root bound.
2. Improved Plant Vigor
Because soil blocks do encourage robust development of root systems while the seedlings are still pretty small, the plant becomes more resilient as it grows.
Having said that, I would like to note that research on whether soil blocking increases yield and speeds up maturity is still ongoing. So such claims are not yet proven 100% true.
3. Easier Transplanting
Like I said in the beginning, soil blockers come in a variety of sizes—from mini-blockers for 0.5-inch (1.27 cm) soil plugs to large 4-inch (10 cm) soil blocks.
As such, it’s quite easy to continue “up-potting” from the smallest soil block by simply directly inserting it into bigger blocks.
4. No Transplant Shock
Now because you don’t need to trouble yourself into taking out your seedlings from a container, you won’t be damaging or disturbing their roots—which also means there’s little to no chance for them to suffer from transplant shock.
This also means they’ll get established more easily and readily.
5. Less Plastic Waste
Another big advantage to soil blocking is doing away with a lot of plastic seedling trays and products, equating to less gardening waste as well.
6. Quicker Clean-Up
Since you will not be using cell trays whenever you start seeds, you also won’t be spending tons of time and energy cleaning and disinfecting them all for the next growing season.
7. More Space-Efficient
Of course, since you have fewer materials to deal with, you don’t have to think much about how and where to store them after you’re done using them.
So in the long run, soil blocking is obviously a lot more sustainable than traditional seed starting.
Is There Any Drawback to Soil Blocking?
As with anything in life, there are—of course—some cons to soil blocking.
The cons of transitioning to soil blocking include the:
- Initial cost of soil blockers
- Time spent on learning and adjusting
- Experimentation with soil block recipes and techniques
- Physical labor necessary for blocking
- Disintegration of blocks from overwatering or dryness
But at the end of the day, the benefits of soil blocking far outweigh the initial drawbacks of getting into it. So if you’re thinking of trying it out, why don’t you start today?
Sources
- “Making Soil Blocks” by Jim Kasten in the PennState Extension
- “Soil Blocking in Five Easy Steps” by Petra Page-Mann in The Cornell Small Farms Program
- “Impact of soil blocks on yield and earliness of six tomato varieties” by Marissa Schuh and Will Jaquinde in the Michigan State University Extension
