It’s time to start thinking about seed starting!
There are many ways to start transplants (often called plugs) and the most familiar comes in the form of a plastic 4-pack or 6-pack of seedlings, or as an entire tray of 50-72 plugs. These ubiquitous plastic forms can be found at every greenhouse and big box store from now until the end of June. They are easy to transport from the store to your house and easy to transport from the house to the garden. But when you go to transplant your new seedlings and you pop them out of their plastic forms, what do you do with the plastic plug containers? Do you throw them in the garbage? Do you recycle them? Do you try to save them for reuse? As we commit to trying to reduce the amount of waste in our lifestyles, these are all questions that should be asked. When I was growing for my own backyard, I would reuse the trays from previous years to start seeds in.
Once I started growing commercially, the plastic plug trays quickly became a bone of contention.
The first issue is storage. I’m growing over 23,000 seedlings this year. Even if I am using a plug tray that allows 72 plants per tray, that’s over 300 plug trays that must be washed, and stored somewhere when they are not in use. That takes up a lot of space!
The plug trays are also far from indestructible. I try very hard to be careful with these trays as the cost to purchase is expensive, but even when you think you are taking it easy on them, they bend the wrong way and break. I have yet to make it to a second season with a plug tray in good condition. This results in extra time and risk of them breaking with plants inside, thus dumping the plants onto the ground/floor in transit or with routine moving.
Lastly, there is the outlying cost for all those trays. $$$
I knew after just a couple of seasons of growing commercially that I needed to find a better, more environmentally responsible way of seed starting.
Enter, the soil block.
A soil block is exactly as the name describes. It is a block of compressed soil that acts as both growing medium and container for the seedling. No plug trays means continuing to reduce the mountain of plastic that has become so ubiquitous with agricultural operations.
Although constructed of only soil mixture, the blocks are not as fragile as you would imagine. And once roots begin to fill the soil block they create a completely stable container that can even handle some roughhousing.
Soil blocks eliminate the expense and storage of plastic containers and they completely eliminate the plastic waste of broken containers.
But the even better news is that this method actually creates a stronger seedling. How?
Plug trays are pyramidal in shape.
A pyramid has only 1/3 of the volume of soil as a cube with the same top dimension. Thus the roots of a plant in a soil block have three times the amount of soil to grow in versus in the same sized plug tray.
This means that the seedlings can stay in the soil block for much longer before needing to be planted in the ground as they have more soil and more nutrients to sustain them. This removes the stress of trying to time transplanting perfectly, especially in early spring when weather can cause unexpected delays.
Another thing that becomes obsolete with soil blocks is root bound seedlings. When the roots of a plant in a plug tray reach the edge of the container, they will begin to encircle the edges of the container. If the seedling is left too long, the roots will circle, and circle, and circle. Resulting in a root bound seedling.
Roots of a seedling in a soil block are “air pruned” at the natural edges of the soil block. The roots of these seedlings will push out towards the edge of the block but once they cross into the air they will die off leaving the portion of root within the soil block “pruned”.
Anyone that knows anything about pruning trees and shrubs will know that when you prune the growing end off of a branch, many more shoots will appear along the branch producing a bushier plant. The science behind this is fascinating.
(Warning: I’m about to geek out here)
The growing point at the end of a branch, shoot, or root is called the apical meristem. The apical meristem produces a hormone that blocks all of the other growing points (buds) further down the stem from growing, thus allowing this top bud to dominate. When the end is cut off of a branch or root, the source of the hormones is also cut off and other buds along the stem will now have the ability to grow. This is what makes a stem bushy. (Like when you’re told to pinch the top off of your basil plant because it will produce more leaves.)
This exact same process is happening at the edges of a soil block. Once the roots push out of the soil block they will reach the air and will be burnt off. Once the apical meristem of the root is removed, that root will branch out and produce many more roots. This means that by the time you are ready to transplant a seedling in a soil block, the soil block is absolutely full of roots that are just waiting to burst out into the surrounding soil. This creates a much bigger, healthier plant, more quickly.
The other reason that seedlings in soil blocks are so healthy is the actual mixture that is created for the soil blocks.
Unlike in standard plug trays, where the soil mixture needs to be light and porous, in a soil block, we are actually requiring a soil mixture that can be compacted. This mixture is composed of peat, sand, and compost or soil. The mixture not only provides nutrients to the growing seedling but upon transplanting the soil blocks you are adding organic matter to the growing area. A staggering amount of organic matter actually.
2” cubed blocks set out at a spacing of 12” x 12” is the equivalent of applying 5 tons of compost per acre!
So every soil block that is transplanted into the soil is one less shovelful of compost that you need to add later.
Soil blocks save time. They save money. And they save mountains of plastic. This year alone, I will sow over 23,000 seeds to be transplanted into the flower field. And every one of them is sown into a soil block.
Have I convinced you to give them a try yet?
The purchase of a soil blocker is required to make soil blocks. The soil blocker is an ejection mold that forms cubes out of your growing medium. But this is a one time purchase that will last. I have used my soil blockers to make hundreds of thousands of seedlings and they still work like new.
Soil blockers can be purchased at Lee Valley, West Coast Seeds, Johnny’s Selected Seeds, etc.
Please note: I have no affiliation with any of these suppliers and I don’t receive anything if you purchase through them.
Except maybe the knowledge that I will have stopped a little more plastic from going into the environment.
Change can start one seedling at a time.
3 thoughts on “Soil Blocking”
Great article Nadine! Sending it along to others.
Warm regards, Donna
As always after reading one of your articles, an inspiration to start growing and utilizing new and tried methods.
Thankyou for this informative article on soil blocking, gardened for many years and have never heard of this tool !