I’ve been starting seedlings for well over a decade. Soil blocking gives me the healthiest, most hearty plants of anything I’ve tried!
What are the benefits of soil blocking?
Soil blocking is an amazing method for home growers and farmers alike to produce seedlings that are stronger, have healthier root systems, and do not incur transplant shock. They are able to be transplanted in almost no time at all with their amazing block system. After the initial investment, it’s more economical to use soil blocking, and it also reduces the waste associated with utilizing plastic pots each year.
How I started seeds before soil blocking
For many years, I began my seedlings the way everyone else does. After they began to really take off, I’d purchase bigger containers and spend half the day transplanting them into bigger pots. It was a pain and I always put it this part off for way too long!
Then I’d have to try to fit all those huge pots under the lights, and then find a place to store all the pots when I wasn’t using them!
This new method really intrigued me.
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Why don’t soil block seedlings experience transplant shock?
Seedlings growing in containers have roots that are never are exposed to air. This makes them keep growing, often wrapping in circles around the bottom of the pot, making them root bound. These roots struggle acclimating to the outdoor soil when they are first transplanted. Usually it takes at least a week to get over the shock and move forward in their growth.
The soil block seedlings have no pots. When their roots hit the air pocket between the soil blocks, they stop growing. Gardeners call this “air pruning”. This aspect is what makes it so special.
How does air pruning benefit my seedlings?
Because of the air pruning, when the roots of soil blocked seedlings hit the edge of the block, they stop growing. The plant realizes it need more nutrients, so it sends out new roots to try to gain the nutrition it’s looking for. This causes the seedling to have a more dense root system, which is exactly what we are looking for! When those new roots hit the air, they also stop growing. This thick root system is ready to grow and immediately takes off when put into the outdoor soil.
Air pruning even allows me to start more varieties of plants indoors and give them head start!
I didn’t like to have to start so many seedlings directly into the ground outside in the spring. I’d struggle with animals stealing my seeds out of the ground, or have issues with germination because the soil was a little too cold. Because soil block seedlings don’t experience transplant shock, I was able to start so many more seeds indoors than normal!
Summer squash, winter squash, cucumbers, and melons are often recommended to be planted outdoors directly in the ground because they don’t transplant well. Those varieties are more prone to transplant shock because their roots get all settled in the pot. With soil blocking, they are actually able to be started earlier indoors and then transplanted outside without that shock. I loved the idea that I could start those varieties indoors with soil blocking, and they could have a huge jumpstart when they hit the great outdoors. Last year when I tried side by side tests of soil blocked squash next to squash planted directly in the garden, the direct sow squash never caught up! I was sold!
Do I need special equipment for soil blocking?
Yes. This is definitely an up front investment, but over time, you’ll save money on the pots you would have used. Additionally, because they take up less space, you can start more seedlings and have a stronger harvest with this new method. I am super frugal and feel like the upfront cost was WELL worth the outcome. If you have a friend who is also a gardener, it would be a great idea to split the cost of the equipment and share them!
The other investment is in the soil. You cannot use regular soil for this, so you’ll either need to make the soil mix or buy it. I’ll detail that below.
Should I make a soil blocking recipe for soil or buy it?
This is a great question! If you’re just beginning, I’d recommend buying the soil your first time around. I feel like there’s a lot to learn in the beginning and I would have been overwhelmed if I had to buy all the soil ingredients up front. I purchased this soil blocking soil from Johnny’s Seeds when I began and it was a wonderful option for me!
With that said, now that I’m into my 3rd year of soil blocking, I felt that it was worth it to buy and store all the components to make the soil. I spent around $100 on all the parts to it, so it’s definitely an investment. But because I know I’ll continue using this for many years, it’s worth it for me. Here’s a list of the supplies I used when making my soil mix.
Soil Mix ingredients
Worm castings (or additional compost)
I wanted to link above so you’d know what I’m talking about, but I bought these from my local nursery, Maria’s Garden Center, and spent around $100 total. So look around and see what you can find.
I like to make mine in smaller batches right now. So to make 88 2″ blocks (just under 2 full 10×20 trays), here is the recipe. This would make a TON of 3/4″ blocks, but I didn’t figure out how many it would make. You can just double or triple this as needed.
Soil Blocking Soil Mixture
Mix VERY well before moving to next step to insure all the nutrients are incorporated
- 6 quarts peat moss
- 1/4 c. bloodmeal
- 1/4 c. greensand
- 1/4 c. phosphate rock
Add next 3 ingredients and again, mix very well to incorporate.
- 2 quarts Perlite (medium)
- 4 quarts homemade or store-bought compost
- 2 quarts worm castings (or 2 more quarts compost)
Add 3 quarts of water to moisten. May need an additional quart. Add slowly to get mixture to peanut butter consistency.
Where do I buy soil blockers
Here are the two soil blockers I started off with. Here’s the link for the 3/4″ blocker and for the 2″ blocker. Later, I invested in a very large one to pot up to for peppers and tomatoes. But in the beginning these two should work! While this is an initial investment, I’m finding that the payoff is great!
How do I make soil blocks?
Making the blocks is relatively easy. I plan on making a YouTube video to show the process, but for now I’ll just explain it. Once the soil is mixed to the peanut butter consistency, you pack it into the blocker. I tend to roll the blocker to make sure it pushes the air out. If you press it straight into the moistened soil, sometimes it can create air pockets. So I roll it 3 times into the mix and then scrape the bottom flat with my hand or a putty knife. After they are all compressed, you just release it!
What do I put the soil blocks on?
I use 10×20 seed starting trays because I have them around so it’s free. Eventually I will buy these trays because the underside is open and provides air into the bottom of the tray. This allows for the air pruning on the bottom of the soil blocks as well. The seed starting trays I use aren’t the absolute best choice, but I want to be careful that I don’t overspend. If I didn’t have them, though, I would buy the ones I linked above.
For the 3/4″ blocks, I use styrofoam trays because they are small. I can’t really use them on the 10×20 seed starting trays because the grooves at the bottom are almost the same size and the blocks can fall into them.
After I make the blocks and plant my seeds, for the 2″ blocks, I cover them with a mix of 1/2 peat moss and 1/2 vermiculite. I just mix it together and very gently sprinkle it over the blocks to cover the seeds. On the 3/4″ seeds, I don’t cover them at all.
What do I do next?
Once the seeds are planted, I follow a pretty normal system. I put them on a 20 watt reptile heating mat but most people use seed starting mats. I top water them with this sprayer until they germinate.
Once they germinate, I put them under shop lights with daylight bulbs and position the bulbs only a couple inches above the top of the seedlings. When the blocks get dry, I gently pour water into the bottom of the tray and allow the blocks to soak it up.
THIS PART IS AMAZING!!
If I planted in 2″ squares, I’m fine. But if I planted into 3/4″ squares, those will often need to move into a bigger block. This is like transplanting them into those 4″ pots like I did before. But now, I just use my 2″ blocker and instead of the seed dibbles, I take them out and replace them with the 3/4″ square dibble. And like magic, I can drop the 3/4″ seedling directly into that 2″ block in a second!
When it’s about a week before I plant them out into the garden, I start hardening them off by moving them outside for progressively more time each day. This is where I’ve killed seedlings a lot, so I should do a post about how to do this well!
And there you have it! Soil blocking!