Winter sowing is a great way to get a head start on summer flowers and even some vegetables.
Using gallon-size plastic jugs, you can create just the right conditions for seeds to germinate and start growing. The process works best for seeds that require a chill period and are frost tolerant during the germination process. Think about annuals that often reseed in the garden in subsequent years, or with planting instructions that indicate you can direct sow in fall or early spring.
When a particular seed germinates is primarily dependent on two factors; day length and temperature. The advantage of this method is that you can emulate the natural germination process in a controlled environment. While direct sowing can work as well, using the jugs you control precisely where the plant grows. My experience with direct sowing is that between wildlife traffic, wind and runoff, autumn direct sowing leaves me wondering what happened to the seeds I planted last fall.
Wait until January or February to start. But start saving and washing your jugs right now.
The basic materials for the method are plastic gallon jugs and a quality potting soil mix that drains well. Seed-starting mixes are not advised because they do not contain the nutrients required to promote the plant growth after germination occurs. Make sure the gallon containers are translucent and not the very white, opaque containers.
Discard the container caps. Mark a line around the periphery of the container just below where the handle starts. You should have at least 4 inches from the bottom of the container to the line. Follow that line and cut around the container, leaving about 2 inches under the handle uncut for a hinge. Using a drill or nail punch, make some drainage holes in the bottom of the container. Fill the containers with 2 to 4 inches of moist soil.
Plant your seeds in the jugs, follow spacing instructions to determine how many seeds to put in each container. Planting too densely may make transplanting into the garden a challenge as there will be too much root disturbance. Small seeds can just be put on the soil surface; for larger seeds, follow depth instructions.
Seal the cut edges of the containers with duct tape. I find the inexpensive duct tape preferable to the really high- end, very tough tapes. Once the containers are sealed, place them outdoors in a sunny, wind-protected area.
Moisture control can be a special challenge in the Pikes Peak region. The containers should be kept moist, but not flooded. Placing the jugs within another container (like a plastic storage box) can help preserve moisture or allow you to add water to the outer container. However, you must monitor the jugs to make sure they aren’t floating in the water. If too much water accumulates drain the outer containers. You can also make drainage holes 1 to 2 inches high in the outer container to control maximum water level.
Once the plants are large enough for transplant, they can be carefully moved out of the container into your garden. Some suggested seeds for this method: petunias, poppies, snapdragons, milkweed, cosmos, kale, broccoli, spinach and Brussels sprouts.
For more detailed information, check out https://extension.psu.edu/starting-seeds-in-winter and https://extension.illinois.edu/news-releases/winter-seed-sowing
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