How to Prepare Your Greenhouse for the Winter Growing Season

September is upon us. Kids are back in school, football is being played on the weekends, and veteran gardeners are starting to prepare their greenhouses for the winter growing season. If you live in a gardening zone where temperatures drop below freezing and snow frequently falls, a greenhouse or a cold frame is your only option for growing during the winter.

If you use your greenhouse year-round, the first thing on your to-do list is preparatory cleaning.

Your home might undergo spring cleaning every year, but for your greenhouse, the most critical time to clean is before winter. If your greenhouse does not stay empty during the summer, the growing season has finished, so there are less plants to worry about. Cleaning is critical to eliminating any pests, such as slugs, whiteflies, and gnats, while also eliminating diseases. Once temperatures start to drop outside, your greenhouse becomes a sanctuary for pests to lay eggs and overwinter. Standing water and clumps of old soil make great nurseries for nefarious insects.

Curious about cleaning your greenhouse? We have a detailed guide here, but here’s a quick outline.

1. Remove everything (plants, tools, shelving, etc.) from the greenhouse. You need to give yourself some space to work!
2. Select a cleaner that is designed for use in a greenhouse. Standard, off-the-shelf cleaners may contain harsh chemicals that can linger and inhibit future growth (even when you remove all of your plants from the greenhouse before cleaning).
1. Looking for a recommendation? Try ARBICO’s ZeroTol® HC. This spray acts as a standard disinfectant that can be applied to greenhouse surfaces, but it also can be applied on plants themselves.
3. Hose it down! Don’t worry about applying the cleaner you selected in the previous step yet. Instead, take a hose and use a jet nozzle to spray down the greenhouse frame. If you don’t have a jet nozzle, you can use a broom to a similar effect, though it’s much less fun.
4. Use your selected cleaning solution to clean the structure of the greenhouse. Make sure that it sits for at least 10 minutes. While cleaning, keep an eye out for holes in the structure or areas that need additional insulation.
5. Check your windows! A mild soap and water solution works fine for this, and a squeegee can speed up the process. Clean windows let in more light, so if you neglect window cleaning year after year, your plants will get a diminishing amount of light.
1. Make sure you open all of your windows and scrape out the grooves. Pests and mold love to propagate here, so it’s important to stay on top of things.
6. Let the greenhouse dry completely before moving any plants back inside.

After you’ve finished your cleaning, decide if you are propagating any plants. 

Propagation allows your best crops to be grown over and over, and it is less expensive than buying new seeds. If you are propagating, prepare the necessary cuttings. We won’t get into too much detail about propagation in this article, but if you are looking to try a new rooting hormone, take a look at Bontone II Rooting Powder. Regardless of if you choose to propagate or if you decide to grow new plants, you should prepare fresh soil for the winter. This is another step to ensure that you aren’t carrying any summer pests through the winter growing season. During your cleaning, you should have removed dead plants, branches, and miscellaneous debris from both the greenhouse and your growing medium. Some growers even transplant growing plants to ensure that their winter greenhouse is 100% free of pests! When placing fresh soil into your pots or trays, make sure that the soil contains the necessary micronutrients and beneficial fungi. Keeping a healthy amount of mycorrhizae in the soil is crucial for developing healthy roots (for both propagated cuttings and plants grown from seeds). Since greenhouses are cut off from the natural soil balance found in a backyard garden, you need to add your own mycorrhizae. The Root Build 240 adds a blend of mycorrhizae that are beneficial to over 90% of all plants, including winter greenhouse staples such as lettuce, tomatoes, and onions.

Growing in the winter isn’t too much different from growing at any other time of year in a greenhouse. What’s critical about the winter season is that it gives you time to reset your growing environment. When you properly prepare for the winter growing season, you ensure that last year's whiteflies and fungi don’t become next spring’s problem.

By: Robin @ ARBICO Organics