I spent a little time during the first couple of days of 2011 getting ready for wintersowing. I've 15 containers so far, most of them clear. There are a couple of containers that are translucent, but I'm following the rule of thumb that if you can see your thumb through plastic, then it will be fine for wintersowing. Each container is very deep: there is enough space in each of them for up to 4 inches of medium, and plenty of headroom for the seedlings. Recommended minimum is 2 inches clearance.
The containers should be cleaned with 10% Clorox and air dried, but unusually for me, I skipped this step. I hope it doesn't come back to bite.
I labeled each container in several places with a number with permanent marker. To avoid being left with a bunch of unidentifiable seedlings due to the sun bleaching the container ID away while it's outside, I covered a couple of ID numbers on each container with duct tape.
Next, I cut each container almost all the way around , about 5" from the bottom to create a hinge.
Next, I filled each container with medium (regular potting soil, not seed starting soil) up to 4 inches deep. Minimum recommended depth is 3 inches. I moistened the medium thoroughly and allowed the excess water to drain, and then sowed my seeds. Where required, I covered the sown seeds with medium.
Finally, I taped the bottom and top halves shut, and put the containers out on the balcony. I left the caps off for ventilation.
There are fifteen containers in all, some in the foreground of the picture, and some between the screen door and the planters at the top of the picture. I plan to wintersow more seeds come February.
Some other notes I gathered from Wintersown.org:
- Control ventilation and drainage by increasing # of holes or taping them over. Start with 5 holes per container.
- Some condensation on the lid is good - don't let the container dry out. No condensation or too much condensation is bad; adjust ventilation and drainage as above.
- Harden off seedlings by increasing size of vents as spring warms up and transplant time approaches
- No need to pot up: hunk o' seedlings method - grab a bunch and plant.
- Don't let the flat overheat, especially as springs warms up.
- Expect high germination percentages, but you will also have failures.
- A couple of days after transplanting, fertilize seedlings at 1/4 strength. Every two weeks, increase to 1/3, then 1/2, then 3/4 strength fertilizer.