Snail Sowing
I am quite interested in plant breeding and one of the forums I follow on this topic contained an interesting post about a method of seed planting and propagation known as the "Snail Sowing" or "Snail Roll" method. Note: Double click on any image to enlarge it.
Basically, the Snail Sowing Method consists of laying out a strip of soil on a fairly impermeable sheet such as cardboard, planting seeds along the top edge and then rolling the soil and seeds up into a spiral until you get something that looks kind of like a snails shell. After germination the plants roots grow down into the soil but are still easily accessible when time comes to transplant. Kind of like a RootTrainer seed tray but not as spendy.
The image at the top of this page shows a spiral which has been unrolled after some weeks of growth. The image at left shows a snail spiral which has been planted up and is beginning to germinate.
Once I became aware of the Snail Roll germination technique I resolved to try it out for myself. The results have been quite pleasing and this page documents the procedure used.
I used Tomatoes and Peppers for my first tests - however I think that any plant that can tolerate transplantation well will work just fine. This means things like curcubits might not be appropriate but even they can tolerate a bit of disruption. The transplant shock just sets them back a week or so.
Step 1: Lay out the Cloth and the Soil
I chose to use weed control cloth instead of cardboard or paper for the wrapper like some people do. The thinking was that it would prevent the roots from penetrating too far horizontally while still letting water and air through. This, of course, is the entire purpose of weed control cloth. Besides, I had a lot of scraps of it which I never seem to be capable of throwing out and this was a good way to justify my hoarding.
I cut a sheet of weed control cloth about 18 inches (45 cm) wide and used the full 36 inch (100 cm) height of the roll The 18 inch width was entirely determined by the fact that I estimated that about 9 inches (23 cm) of depth of my home made potting soil would be adequate and also that I had a 9 inch plastic pot handy. The image at left shows how the first 9 inches of soil were placed. The other half of the cloth will be folded on top of this soil once the seeds are planted so don't put the soil past the halfway point.
In particular, note how the soil goes right up against a hard edge of the bench. If I did not have a metal lip on the bench I would have found a length of board and used that. I find it is useful to have a hard edge because it keeps the soil on the top of the spiral nice and square and, for some reason, that sort of thing really matters to me.
Step 2: Plant the Seeds
After laying out the cloth and potting soil, plant the seeds along the edge. The distance from the left hand edge will effectively be the depth of the soil the seed is planted at so pay particular attention to that. The image at left shows some Tomato seeds being planted. The distance you see is probably a bit deeper than I would usually use for Tomatos but they all seemed to germinate OK so it appears I got away with it.
The soil has been gently tamped down so as to ensure it is flat and and has a consistent depth of about 1/2 inch (1.5 cm). The seed is also now in firm contact with the soil. This is probably not necessary for the seeds but makes it easier to roll the thing up in the next step.
At this point I also watered the potting soil and seeds with a very fine mist. Besides having the effect of getting just the right amount of moisture down deep in the soil it also made the soil a bit more gummy and hence was another thing that makes it easier to roll up in the next step.
Step 3: Roll up the Snail
Fold the right hand side of the weed control cloth (the part without the soil) over onto the left hand side. The right edge should just meet the left edge - if it does not, then add or remove some soil from the center area until it does.
Pick an end and begin to roll up the weed control cloth. Note that the soil has a layer of weed control cloth on each side of it top and bottom. This makes it much easier to roll it up. If you do not double it up the soil tends to fall out the bottom and go everywhere (I speak from experience).
The image at left shows the folded weed control cloth being rolled up. Don't roll it too tight - you do not want to compress the soil too much. Alternately, do not roll it too loose either. The tightness of the roll should just compress the soil slightly to put the seed firmly in contact with it but no so much as to make it hard for it to germinate.
Step 4: Tie up the Snail Roll
Now tie up the snail roll with a bit of string. This holds it together nicely.
At this point you should have a roll of soil and seeds in a weed control cloth spiral. The left edge is nice and sharp and the right hand edge is completely sealed up and the soil cannot fall out.
Step 5: Put the Snail Roll in a Pot
Pick up the snail roll and place it soil side up in an old plant pot. I have a multitude of these things and so it is not too much trouble to find one that fits. I like to have the top of the snail roll be just level or slightly below the top of the pot. Fill in around the spiral with extra potting soil. This isn't for growing - it just assists with moisture retention and stops the spiral rattling about so much.
The image at left shows the spiral in the pot before the extra soil has been added around the outside.
Step 6: Let the Seeds Grow
Wait a few weeks and let the plants grow. This should take pretty much exactly the same amount of time as if you had used a more traditional method of germination.
The plants will look all bunched up and crowded but, in reality, if you spaced the seeds far enough apart when you were laying them out then their roots will not be competing with one another. The roots will be growing downwards into the deep rooting medium at the bottom of the spiral.
Step 7: Open up and Transplant
When you think the plants in your Snail Roll are large enough just take the spiral out of the pot, lay it flat and unroll it. You should see some nice strong plants with roots heading downwards. The roots should not have penetrated into the weed control cloth (very much). Individual plants should be easy to separate and transplant. If you have too many plants just roll the spiral back up and replace it in the pot. If you add more filler soil around the outside to compensate, most plants will largely act as if nothing happened.
The Snail Sowing method really seems to work. I intend to use it increasingly in the years to come. It is much easier and simpler than messing about with potting trays. Also, as an added bonus, it uses considerably less potting soil per plant and takes up far less space on the greenhouse bench than the equivalent number of seedling trays would do. For me, at least, bench space is always a premium in the spring.