What are soil blocks? I first learned about soil blocks after watching The Real Dirt on Farmer John movie. He uses them to start seeds and then I saw that Eliott Coleman recommends them. A block of soil is made and with the right mix will hold together during plant root growth. Once the roots grow into it, it will be more solid. It eliminates the need for flats, peat pots, paper pots and any other pot which can get root bound. In the soil block, roots will air prune and not go beyond outside. It is a messy operation, but for those who like to tinker with things in their workshop, I made a 3/4" blocker to try out. A soil block is supposed to help minimize transplanting shock. Remember that soil blocks can dry out faster than soil in flats or pots. Keep an eye on them. You will have to water 2 times a day at least. Also, this small block can disintegrate quickly if you pour a lot of water on it. Use a mist sprayer only.
With this mini soil blocker, it is possible to make 144 and they would fit under a 1' x 1' space of a grow light. This is what makes this nice. You can start many seeds in a small area. You only have about 2 weeks growing time maximum, then you must transplant into something larger like a 2" soil block, recycled cups or flats. Transplant shock should be minimized because the roots are not disturbed. You can see my other instructable on making the 2' soil blocker if interested in that. See here https://www.instructables.com/id/Making_a_Soil_Blocker/. After it outgrows the 2" container, anything bigger than that, I would just transplant into the bottom of the half gallon square milk carton or orange juice carton cut 5" high. I don't think there is a need to make a 4" soil blocker, but you could.
This is good for the home hobbyist. If you experience good success and want to try more, I would invest in a professional soil block maker that can do multiples at a time.
See this site http://www.pottingblocks.com/ for some great advise and ideas on the soil block method. I am not affiliated with it. The gentleman who runs the site is very knowledgeable and helpful in returning emails. He also has supplies and square soil block makers at reasonable prices. I learned a lot from all of the content he shares.
Step 1: Making the Cutting Tube
Get a soda can and cut the top and bottom off. Tape down to a board and make a straight cut at the top. Measure 3" down from the edge at a few places so you get a good parallel cut for the bottom of the tube. Make a perpendicular cut (right angle to the last cut you did) on the left side. Measure 5" for the length of the tube. Now you have your tube material.
Step 2: Dowel and Tube Assembly
Cut a 3/4" wood dowel to 7" long. If you have an 1/8" dowel, you can use to make a 1/8" x 1/8" extension at the end of your dowel to make a seed depression . If not, you can just make a 3/4" block and poke the top later (carefully as not to split the block open) with a pencil.
Take the aluminum and roll around the dowel. Leave some play and don't make it tight. You will need it to slide easily to pop the soil block out. Wrap the tube with 3 pieces of black electrical tape. You could also use something more permanent like JB Weld and let dry over night.
Step 3: Soil Block Mixes
3 buckets brown peat (standard peat moss, use a premium grade)
1/2 cup lime. Mix ingredients together thoroughly.
2 buckets coarse sand or perlite
3 cups base fertilizer (equal part mix blood meal, colloidal phosphate, and greensand). Mix.
1 bucket garden soil
2 buckets well-decomposed compost. Mix ingredients together thoroughly.
- From The New Organic Grower, by Eliot Coleman
Or you can use any good organic potting soil. I found a bag of Master Nursury Gardener's Gold Organic potting mix and it works great. I did make my own blend as above too, but it was expensive and time consuming trying to locate greensand, colloidal phosphate (gave up - could not find), etc.
Add 1 part water to 3 parts soil mix. Mix to a soft putty or wet cement (not soupy). A soil block needs to have the soil packed tight. Rinse out blocker in bucket of water after each block is made. This will help release each new block made.
Remember that soil blocks can dry out faster than soil in flats or pots. Keep an eye on them.
Step 4: Soil Block With Broccoli Seedlings Started
Here are some broccoli seedlings doing well in the soil block. They will need to be transplanted very soon. You will see there is a line drawn on the dowel up 2 1/4" from the bottom. This is where you line up the top of the tube. Here is how you make a 3/4" high soil block.
1) Hold you thumb on the tube to secure to the dowel edge at that black line on the dowel.
2) Plunge into your potting mix. Press in so that the block is very firm. You don't want it loose. The block will fall apart. Keep holding the tube to the line and you will get a 3/4" high block.
3) Push out the soil block onto a sheet of plastic or wax paper.
4) Plant seeds
5) For a small amount of blocks, I used the bottom of the 1/2 gallon orange juice carton
Step 5: Put Under Grow Light
Cover with plastic, and place on top of refrigerator. Check 2-3 times per day and keep moist, not soaking wet. Lightly mist. Remember, these will melt like butter if drenched in water.
I used a $10 shop light with GE Kitchen and Bath flourescent tubes for my grow light. I don't get enough sunlight in a window. Seedlings become too tall and leggy if they don't get good light. These tubes were tested on Wayne's This and That webpage http://www.waynesthisandthat.com/fluorescent.html and showed good results compared to the other types of fluorescent tubes. I have the seedlings about 2-3" away from the bulbs.