For a passive greenhouse in mild to moderate climates, (most of the continental US), a full year-round growing schedule is not only practical, but ideal. You’ll enjoy the widest variety of fresh food throughout the year and take advantage of any free yard space to maximize your summer and fall harvests.
For greenhouses in the extreme northern (or southern) latitudes, your greenhouse activity in the wintertime will depend on the hours and angle of sunlight available in your area, unless your setup provides excellent insulation, supplemental heat, and adequate artificial light.
Day Length
This is one of the most important factors when it comes to determining your greenhouse planting schedule. If you’re only using natural light, it’s essential to know what the average day length is in your area. Typically, seedlings need about 10 hours of sunlight each day. In the winter, as days become shorter, plant growth slows significantly. This can be altered by introducing artificial lights.
Temperature
The ambient temperature within your greenhouse is another essential consideration. The areas of your greenhouse closest to your vents will be cooler than other areas. This should be where you place your plants that are able to withstand cooler temperatures, such as spinach, kale, lettuce, etc. The warmest parts of your greenhouse will likely be along the north wall, this is where the sun reflects off the wall, directly hitting those plants. Ensure that plants found there can handle the warmer temperatures, and more direct sunlight.
Winter: This is typically the toughest season for a passive greenhouse, this is where it’s most important to match your crops to the conditions your greenhouse can support.
Frost loving vegetables: If your greenhouse gets pretty cold (frost but no freezing), you are definitely still in luck for a tasty wintertime menu. Leafy greens and hardy root vegetables are excellent choices in this case. A few excellent winter options even improve their taste after exposure to a good frost: Kale and cabbage, carrots, parsnips, beets, collards, kale, leeks, and cauliflower.
Staggering your harvests: While in other parts of the year, it makes sense to harvest all of your crops over a short time span, you’ll want to spread out your harvest during the winter. This means being smart about scheduling, harvesting only as needed, and allowing plants that regrow to do so. It may make sense to plan out your beds in rows that are harvested one after another. This allows initially harvested rows to regrow and repopulate while harvesting other rows. This ensures you’re able to access fresh veggies and fruits throughout the winter months.
Spring: Early Spring is the time to start seedlings that you plan to transplant outside once the weather warms up. This allows you to grow a larger variety (or just more) of warm weather vegetables than your greenhouse alone could support.
These seedlings should be allowed to sprout in the warmest, most protected parts of your greenhouse. Once old enough, they are then transported to the cooler, less insulated sections of the greenhouse in order to harden and become more durable.
If your seedlings are well-established and you’re itching to plant more, but there’s still danger of frost, consider using cold frames to protect your young plants from nighttime extremes. This will give them a protected environment for hardening off, and it’s a simple matter to lift off the cold frame once the risk of frost has passed.
