Try 1: I followed the directions for soil block starter mix and a tray design by Eliot Coleman, although I didn’t have greensand or other organic potash sources available. I decided to go ahead anyway and started a tray with seeds for spinach, scallions, leeks, kale, and parsley. After planting, I placed the tray on the drying rack I had over my garage heater. I watered the blocks 3-5 times/day using a spray bottle but still found the blocks were drying out quickly. I began dumping water onto the blocks about once a day, but had some seeds begin to wash out periodically. The spinach sprouted fairly rapidly, but other seeds didn’t sprout at all. Once the spinach reached 1 1/2-2″ I hung a fluorescent light 1-2″ above the tops of the plant tops based on various instructions I found. The drying out increased. I later moved the light up to try to help with drying out. After several days of 14 hour/day light, the spinach withered.
Try 2: I replaced 1/2″ MDF bottoms, which seemed to be absorbing the water and swelling, with plywood. I also had gotten some large clear plastic bags with a couple of plants I purchased for valentines day at our local garden center, Prairie Gardens. These fit around the tray nicely. I also purchased some Greensand from Amazon.com and added that to the mix. Finally, I purchased a soil thermometer and confirmed soil temperatures to keep it fairly consistently at 70 degrees. The bag was kept closed with a clip except for watering. Several spinach again sprouted quickly. Best of all I’ve been able to reduce watering to 2 times/day with little drying of the soil. Once spinach reached 1 1/2-2″ I turned on the flourescent lights for 14 hours/day at around 5″ above the plant tops and began leaving the bag partially open to avoid over heating. Seeds continue to germinate.
February 28 (~ 1 week after planting): Spinach – 50% germination; Scallions – 50% germination; Leeks – 75% germination; Thyme – 100% germination; Oregeno – 100% germination; Sage – 50% germination
March 2: Spinach – ~2″; Scallions – ~2″; Leeks – ~1″; Thyme – 3/4″; Oregeno – 1/4″; Sage – 1″, additional 25% germination
March 10: Spinach – full 2″; Scallions – ~3″; Leeks – ~2″; Thyme 3/4-1″; Oregeno – 1/4″ Sage: 1 1/2″
A second set of soil blocks were put in a tub with water at the bottom, with seeds elevated on PVC plants. The conditions were otherwise similar. My thought was to see if water inside the bag would help keep the soil blocks from drying out more. The blocks did seem more moist, but germination rates ended up being much lower. Over time water levels over ran the PVC tray and began eroding the bottom of the soil blocks. I won’t do this again.