Simply put, overwintering is the process of plants reacting to “winter” conditions such as freezing temperatures, ice, and snow. Some plants will need no intervention to survive. Others will require special attention or care to prevent them from subsiding to winter conditions. I discuss the process and options below.
Growers, gardeners, and farmers have little time to spare. Aside from the usual fall preparations going on inside your greenhouse, there are other considerations for plants that might be exposed to the elements. While overwintering might sound like it requires extra work, it can save you both time and money in the long run. There will be a bit of time front-loaded into these preparations, but they are worth the effort.
Here are just a few advantages of overwintering to consider (depending on the tactic you choose):
- Earlier spring harvests
- No need to replant
- Avoid repurchasing same plants each year
- Chill sweetening root crops (more on this later)
Your Decision Depends on Hardiness
Each plant will have different requirements for overwintering techniques. If you’re not sure what your plants can withstand, consult the USDA Plant Hardiness Zone Map.
Just type in your zip code and the map will pop out your hardiness zone. If you have plants outdoors that won’t survive the winter in your specific zone, you need to overwinter those plants or you risk losing them to the cold. When purchasing plants, you can often find this information on the display card or someone working at the garden center or nursery can help you figure this out.
For instance, we are in zone 5 and 6 here in southern New Hampshire. This means that the annual minimum temperature is between -15 to -5 degrees Fahrenheit. We can then identify the plants that will be able to withstand these temperatures with or without intervention and then plan accordingly.
Plants that cannot survive will have to be brought inside, placed under a cold frame, or… well let’s take a look at the several options.
One tip is to plant cool-weather crops such as kale, beets, broccoli, and spinach in the early to mid-fall. They will establish root systems in October and November, fall dormant during the cold dark months, and then emerge early in the spring. So while your neighbors are struggling to dig up ground and get in seeds, you’ll have sprouting plants.
Other plants are less resilient. Less cold hardy perennials will need to be brought indoors. Planting in pots expedites this process, as the plant can be moved much easier. If you have room on a windowsill or in a room with moderate amounts of sunlight, you can bring herbs and succulents such as chives, mint, rosemary, parsley, and oregano indoors. The humidity levels should be monitored and a fan will keep the stems stronger. The plants will grow slower in these conditions but they will most often survive with adequate attention.
If you don't have the space for this option, then here is an alternative. Once the plant goes dormant, remove them from the garden and store them in a dark, cool place such as the basement. The plant will not grow in these conditions, but it will survive. Light and warmer weather will jumpstart growth. But beware, bringing these plants indoors might shock the plant and potentially kill the root system. For such plants, take a root cutting and keep them in the house in soil over the winter is another safeguard.
Most perennials, as the name suggests, will survive through the winter with minor bed preparations. These plants will persist each year but there are a few steps to help them thrive year after year.
Some, like Hardy hibiscus, will remain dormant throughout the winter. They naturally enter dormancy in hardiness zones 4 through 9. You will see the leaves fall off and the plants will appear dead after the first frost. But not to worry. Come spring they will return.
With this plant, and others that can survive the elements, we suggest trimming dead stems back to the ground. This prevents new growth during brief periods of warmth during the winter. You can also place a layer of mulch over the roots, 8 inches deep, to insulate the plant against the cold. This also prevents early sprouts that will likely not survive and delay the plants ability to flourish in the spring.
More On Chill-Sweetening
Root crops such as beets, carrots, and turnips have defense mechanisms to ensure survival during the freezing months. The best part of this phenomenon is that it actually makes them taste better come harvest time. The survival tactic works by converting starches into sugars. The stockpile of sugar keeps the plants from freezing, and, in turn, they are more crispy and snappy as a result.
And, of course, one suggestion to avoid this entire process is to place the plants in a greenhouse. Specifically, a heated greenhouse in colder regions. We have a plethora of options to consider for growers of all needs and requirements.
Did we miss any useful overwintering tips? We’re all ears! Let us know below and let others in on useful tactics for preserving those beloved plant until next season.