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 2" and 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.
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 for some great advise and ideas on the soil block method. I am not affiliated with it. http://www.pottingblocks.com/ 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: Parts and Tools
These are the parts and tools you will need to make:
2" inside diameter PVC pipe
3/4" wood dowel
circle cutter for use in drill press only
3/4" forstner drill bit
hand saw - not shown
Polyurethane - water based or similar to seal
3/4" wood screws
3/4" thick wood scrap (I used Pine)
The drawing shows the idea of the soil blocker. You can start off a seedling in a 3/4" block then transplant to the the 2" block, then a larger block or pot. No shock to roots.
Step 2: Cut Out Disks
Cut out 3 disks, each a bit smaller than the inside diameter of the pipe. Cut 1 first to check fit. Remember, the wood will swell a little when wet. It will swell even after sealing it. Don't make it too tight. The top disk can fit tightly in the pipe top. This piece won't move when installed. The plunger needs to fit loose just so that it can push the soil block out without too much effort.
Step 3: Drill Holes
Layout for a 3/4" hole. Use carpet tape to secure the disk to the drill press top. Line up your marks and drill. You need to get perfectly centered. There is no center punch to guide, so this is why you need to carefully lay out your 3/4" hole on cross hairs and boundaries on top. Drill 2 disks all the way through. Drill the disk top handle about 1/4" deep only.
Step 4: Dry Fit and Assemble
Cut 3/4" dowel to 6" long
Glue in 3/4" dowel to the handle disk
Cut the pvc pipe to 3.5" long.
Put top disk in flush with the top. Drive a screws into opposite sides to secure.
Seal with polyurethane (3-4 coats)
Put handle rod assembly into hole
Attach plunger disk flush with bottom of rod for a solid soil block. Secure disk to rod with a screw.
Or attach plunger disk 3/4" up from bottom of rod to make a soil block with 3/4" hole to accept a 3/4" soil block transplant.
Put some candle wax on the 2" plunger disk if tight to help smooth the stroke.
Step 5: Finished Assembly
Here the finished soil blocker with tomato plant that was started a few weeks ago.
Step 6: Soil Block Mix
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. Good luck!
Step 7: V8 Can Prototype
First I made a 2" blocker from a V8 can. It did not hold up very well and I would not recommend using. The aluminum is too flimsy.