Last night I created 300 soil blocks that I will use to start seeds growing indoors. I will be planting vegetables, herbs, and flowers for transplanting to my raised bed edible garden and the foundation planting in front of my house which I'm redesigning this spring.
Soil blocks are compressed soil in a block shape. They are made using a special soil block mold maker. Different types of soils, my homemade compost and different organic fertilizer items are combined in a special mix for this project. Water is added to this mix and then the blocks are made.
When the seed grows in the block, when the roots hit the exterior the air seals them off. This keeps the roots strong and prevents roots from becoming overcrowded or root-bound as can be the case when raising transplants in pots. Another great thing is the strong roots exposed to the air do not get root shock at transplanting time as pot-grown transplants can. Lastly dumping the tender seedling is not done, a process which can sometimes damage not only the roots but the fragile stem itself.
There is no waste here. There is nothing to throw in the trash or to rot. The soil block goes right into the garden and that's that.
I first learned of this process in the 1990s on a gardening show that used to air on cable TV's The Learning Channel, "Gardening Naturally" featuring Eliot Coleman and (his wife) Barbara Damrosch. I found the recipe for the soil mix in Coleman's book The New Organic Grower. This book is excellent although perhaps a bit overkill for the home gardener, it is geared toward small family farms but I found it contained information I could not find elsewhere. I bought it back before the Internet really expanded so honestly I don't know how much of this is available online. I value Coleman's many years of experience. If you are interested in gardening year-round or gardening in the colder climates, check out his subsequent book Four Season Harvest.
(I see that Johnny's Selected Seeds sells a potting mix for this. I've never used that, I make homemade using the Coleman recipe.)
For soil blocks this is what I do. I do own all three sizes but for me, a home gardener with a high germination rate, I didn't feel the effort and time was worth it to use the tiny soil blocks ("mini 20").
Also since I plant my transplants out about 6-7 weeks, I don't need the four inch size soil block maker ("large single"). To try to gain 1-2 weeks of extra indoor growth for my zone 6 garden, this seems too labor intensive for me. People living in cooler climates who need longer time growing transplants indoors might find these necessary. (Given the price this thing sells for today I should consider reselling my barely used 4 inch mold!)
So, the bottom line is I only use the two inch soil block maker ("medium 4").
The mold makes a little hole for the seed. I place vermiculite on top of the seed. I have these in plastic trays with solid bottoms ($1-$2 each at a garden supply center). I water them by putting the water in the bottom of the tray. I don't water from above as I find it can disrupt the germinating seed or the tender seedling. I grow these under lights in my basement using a 40 year old shelf system that my father made out of wood for my mother when she first began hybridizing and showing African Violets. When she quit the hobby she passed on the shelf to me. (Now that she has restarted she has not asked for this back which makes me very happy.)
I don't recall where I bought these but now they can be found at Johnny's Selected Seeds.
I do not use heat trays, never have bothered to. My seeds are started in the basement close to the furnace. It is usually in the 60s in my basement near the furnace.
Here is a video tutorial about making soil blocks. I almost made one myself until I realized there are some online now, so here you go.
Amazon now sells the soil block makers.
Related post of mine: My Experience with Soil Blocks for Seed Starting
Here is the one I use:
I own the giant one but don't use it.
I own the mini one but don't use it.
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