Saturated with water and laid on soil, they will keep the top of any bed underneath them comfortably moist for a lot longer than bare dark soil, especially on sunny days. Not only does this preserve precious water and avoid its high cost ($6/cubic meter, I’m told), but you are less likely to lead a seed to think it has the right conditions for germination only to go away for the day while it bakes to death. The moist sacks also keep the soil much cooler which is to their liking.
The reason why this technique is so important to us right at the moment is two-fold. First, we are trying to germinate a lot of cool weather crops in very warm sunny conditions. Second, we are trying to do so with Johnny’s aforementioned precision seeder which is finicky about the cleanliness of beds. Small stones, roots, even soil that is a little too powdery make furrowing the seed really difficult. If the seeds could be easily buried by a half an inch of soil like the seeder would like to do if it had Eliot Coleman’s always-perfectly-moist loamy soil, then the burlap sack technique would still be beneficial but not critical. In our case, although we are fortunate to use the seeder at all, it requires us to set it up to not dig furrows at all but to drop the seeds on top with no furrow.
For the radishes a couple of weeks ago, I sprinkled Special Blend potting mix or plain soil on top of the dropped seed (soil’s cheaper and works as well but takes a bit longer to apply) to act in lieu of placing the seed in the intended furrow. That was so two weeks ago. Instead of a soil cover, we now soak coffee sacks in water and then gently place them on the just-seeded beds. Even in hot weather, we can get by watering once per day although we do water lightly at least twice just to be sure.
The carrots started coming up sparsely at 5 days and, in great numbers, at about 8 days. Hakurei turnips, spinach, beets, kale etc germinated in a day or two. I start taking the sacks off once I start seeing a little green or when I feel as though leaving them on would start to impede their growth. I have recently read that someone has successfully ripped out weeds that have grown through the burlap but I’m finding that, except for the grass, we hardly have any weeds. And the grass just laughs at any attempt to weed it without digging down to its roots.
The sacks vary a little in size but are all close enough to bed width of 30″ that I use them all with no modifications. When they’ve done their job on a bed, I’ll let them dry out before folding them up and stacking them somewhere.
We were about to put them away this morning and then realized that they would probably work just as well on the numerous plant trays Pauline has started for her new plant start product line (which I hope she will write at some point). Happily, three standard trays laid side to side get covered almost perfectly by one sack.
This technique really isn’t a “farm”-scale option but I still think it’s quite clever and, if nothing else, really demonstrates the degree to which moisture is important in germination. The precision seeder is appropriate for the small scale farm (i.e. a scale bigger than the large garden we’re currently growing on) as far as I can tell but I’ll either have to figure out how to make it furrow without getting stuck, or continue using coffee sacks for germination.
Before the roasting operation of Salt Spring Coffee moves to the mainland in a few months, Salt Springers have access to free burlap coffee sacks, used only once. From (a now better-paid organic grower) Juan Valdez to your soil, for the price of a trip to the RoCo (Roasting Company aka SS Coffee).