“Winter seeding” has become the descriptive for a seeding technique that I’ve done for decades, but didn’t use that exact term. It’s basically just sowing seeds in a container and placing the container outdoors where the seeds are exposed to the elements over an extended period, so that they freeze, then thaw, then freeze again repeatedly. This stratifies the seeds so that they can germinate at the appropriate time. This procedure works only for seeds that would normally be outdoors during freezing weather, not for seeds of tender, frost sensitive plants so one mustn’t use this technique for basil, petunias, or other seeds that may die if frozen after they become moist.
I’ve done winter seeding in all types of containers, from wooden boxes to old plastic tubs, recycled cottage cheese plastics, and old buckets with holes in the bottom. Holes in the bottom is a key to success for any planting container because drainage is a must. If your container does not have holes, make some! In recent years recycled gallon jugs have become the container of choice, partly because they are readily available but mostly because they are light weight, transmit light fairly well, hold up to the weather, can be closed or opened easily for temperature and moisture control, and are somewhat critter resistant. Now that I’m not growing commercially, they also are a good size for growing just a few plants. I like 4″ of soil at least, because there will be several plants in a small space, and they will be in the jug for an extended period so roots need to be able to go deep.
I leave the caps on for the first few days. The potting soil was moist, and the seeds need to absorb that moisture. Most seeds were covered with a bit of soil, but some like the Shasta daisy need light to germinate, so they aren’t covered. That means they could dry out quickly if the cap were off. Be sure to check germination requirements for light/darkness when seeding. I’ll keep an eye on them with a look every couple of days. If we get a bright sunny day, with higher than normal temps, I’ll take the caps off during the day so the seeds won’t bake, and put them back on before night. Since the jugs aren’t taped all around the cut, there is still a bit of air movement, which is a good thing. As soon as I see any germination, the caps will come off and stay off unless it’s going down to single digits F. The crate of jugs was moved to the berry box over an empty raised bed in the potager. There is no plastic on this berry box, so the jugs are open to the elements.
Winter seeded: Primula “Oriental Sunrise,” Lupine “Gallery Blue,” Aster “Light Blue,” Aster “Goliath,” Cornflower “Blue,” Anemone multifida, Shasta daisy “Prieure.”
The nice thing about winter seeding, besides being so easy and not requiring any indoor space or special lighting, is that the plants are already pretty well hardened off. When they get about an inch tall, I’ll take the tape off and open the jugs on nice days so the seedlings start to get a little wind. When they get true leaves and are 2-3″ tall, I’ll transplant the larger ones into individual pots which will go right back into the berry box, with a layer of floating row cover available if it happens to go into the teens, and an extra cover over the top of the berry box if it goes below zero. (Just be sure the floating row cover is supported at intervals in case of heavy snowfall.) This expansion from 1″ to 2″ or 3″ takes longer than one might think, because growth in winter at low temps during shorter days is much slower than in spring. By the time spring does arrive, they will be sturdy plants with dense root systems and be ready to go right into the gardens. In the meantime, the smaller seedlings still in the jugs will have more room to grow and eventually be transplanted as well. I prefer to transplant them into individual pots because if left in the jugs too long, the roots become so entangled they are nearly impossible to separate. Any damage to the roots during separation can set the plants back, although it rarely is fatal and they do eventually recover.
So, the 2021 gardening year has begun, in just a small way to be sure, but it feels good! And, I’ve decided that if I’m going to be gardening again in a few months, I’d better get this old body back in shape, and a little stair climbing just might help!