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10 Helpful Steps to Overwintering your Plants

What is overwintering? Quite simply it is the process of simulating the season of winter for your plants in a controlled environment. By carefully controlling the amount of light, water, fertilizer and frost a plant is subject to, you can create a safe ‘winter’ state for your plants and help them survive even the harshest winters to bloom again. Stretch your gardening budget year after year by saving tender perennials in containers and hanging baskets.

Overwintering your plants sounds complicated, but it really is quite simple - follow the easy steps below and you can overwinter successfully.

  1. Are Your Plants Happy?
    Healthy plants are happy plants. Just as this is true for spring and summer, it holds even more truth in winter. Your plants stand a much better chance of surviving through the winter if they are healthy. This just makes good sense. Different varieties of plants may benefit from one last feeding before going dormant for the winter so it is a good idea to check with your local nursery or Master Gardener division for proper feeding advice.
  2. Shoo, fly!
    Pests are a nuisance throughout the warm months, and the cold doesn’t change things. Your plants need to be pest-free before going dormant to prevent an attack when they can't fight back. While it is too late for ladybugs, you can use whitefly traps and organic sprays to eliminate any remaining pests. Inspect leaves carefully before moving into a greenhouse; if a plant looks infested, don't bring it in.
  3. Mmm, Mulch!
    Mulch is a gardener's best friend. Mulch helps your plants retain moisture and adds extra heat, keeping their roots happy. The short amount of time it takes to make mulch is rewarded not only during the winter months but long into spring and summer as the mulch decomposes and adds rich organic matter to your soil. Grass clippings and torn or shredded leaves are simple to use and are readily available. Applying a 1½-2” layer of mulch offers great protection. Inside a greenhouse compost is a good mulch. While leaves and grass are great for outside mulch they may harbor disease and your greenhouse environment must be a clean one. Coco is a great greenhouse mulch; it is clean, holds moisture well and traps air. Trapped Air = Insulation.
  4. Drink Up!
    Just because your plants are not blooming or creating fruit for you, doesn’t mean they aren’t thirsty. While their water requirements do diminish during the winter, they still need some water if they are to see the sunshine again. Watering up to one inch per week is recommended but don't overwater; cool moist environments harbor disease.
  5. Prune Early!
    Too much change can be a bad thing. Make sure you prune early and leave at least 6 weeks before your expected first frost. How much should you prune? Cutting off any dead limbs or unhealthy growth is a good start. Some plants will thrive with a healthy prune while others may not fare as well so it is a good idea to do a little research before you start snipping away. However, be careful to not wait too long to prune or your plants may not be able to harden off before winter. The shock of the cold could do some serious damage. This is also a great time to take cuttings and divide your plants.
  6. Bundle Up!
    Use frost shield bags and blankets to bundle up your plants. Just be careful if you use plastic sheets; they are not insulated so the cold it conducts may actually freeze the foliage and do more harm than good.
  7. Heat Up!
    Most plants are perfectly happy to overwinter well into the 30's so an unheated greenhouse or cold frame is a great way to protect your plants from the elements. If you find your plants are actually growing you can lower the temperatures by letting in more cool air, just be careful to keep the soil temperature above freezing. In some areas a small heater is needed in order to regulate the heat at night, but make sure the greenhouse doesn’t get too warm during the day. Use your ventilation system to draw in the cool outside air to help regulate the temperature in your greenhouse to keep your plants dormant. Plants don't like to be locked up without fresh air, so even when it's cold out they still need some ventilation.
  8. Where’s the Sun?
    Most plants will tolerate a few months of lower light levels while overwintering. Keep your eyes open for yellowing or pale foliage, dropping or drooping leaves, and leggy growth. Any of these can mean that your plants need higher light levels and you can either relocate your cold frame or greenhouse to a sunnier location or supplement with grow lights. Some plants will completely die back and that is okay. They will still do well if they avoid a hard freeze and they have the benefit of an earlier and warmer spring when they are overwintered in the right conditions.
  9. The Great Outdoors!
    Slow is the way to go in the spring, after the last frost has past. It is a good idea to bring your greenhouse temperatures up in the spring to get your plants ready to be moved outside. Approximate temperatures of 65° during the day and 55° at night will help your plants transition from winter weathers to spring and prepare them to staying out all night. Once the last frost date has past you will want to give your plants a few days in an intermediate zone, like a covered porch or under a tree canopy to prevent sunscald before moving into direct, daily sun.
  10. Oops!
    It happens… some of your plants don’t look quite as happy as the others as spring nears. But don’t give up on them – they may return to life again. Prune back any dead tips or branches to just above new growth and wait and see.
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