Winter is upon many of us and our gardens are already asleep until spring. However, those in mid-range states and warmer climates still have to worry about the encroaching cold. When extreme swings or unusual cold in otherwise warmer climes is not the norm, then sudden cold snaps can be especially damaging.
So next time you hear the weather report, here’s when you need to worry and how to protect your prized landscaping!
How Chill Damages Plants
One of the hardest things for all plants to tolerate is wild temperature swings. Check out our Garden Blog to ensure your landscape is winter-ready.
Spring's early warm patches may push out plant growth or flower buds prematurely - then suffer when a frost hits. Autumn can have warm bouts of weather followed by drastic temperature drops at night and the damage won’t show until spring!
These changes in temperatures are more common in the turbulent weather of today, so pay close attention to the forecast in spring and fall.
When Should I Cover My Plants?
Frost and freezing occur when temperatures are at or below 32°F (0°C). Frost-tender plants are damaged under 40°F if the plants are in low areas where cold air sinks. Plus the weatherman isn’t always 100% correct, so any time it could possibly dip near your plant's tolerance range is when you should act.
Types of Plants to Protect From Cold
Factors to consider before you cover everything in your garden with your favorite linens:
- A plant or bulb that’s non-native or outside your growing zone
- Newly planted plants
- A plant that just leafed out or bloomed
- Sheltered -vs- exposed locations
- Seedlings or houseplants that are not hardened off yet
- Protect tender perennials in spring and fall
Weather Terminology:
- Cold Weather Advisory - Typically 32°- 45°F
- Frost Advisory - Light frost warnings are between 29°-32°F
- Freeze Warning - Moderate freeze between 25°-28°F
- Hard Freeze - Temperatures 25°F and below. The ground is frozen solid.
Remember, it is not just the temperature to be concerned about - but the length of time during which temperatures remain at or below freezing!
Types of Frost Damage
Frosts can either break cell walls due to swelling and expansion or evaporate moisture right out of the plant like wilted spinach. While there are many scientific names like advection frost, radiation frost, and evaporation frost, gardeners need to worry about:
- White frost - Ice forming on the plant's exterior because of humid air, calm winds and clear skies.
- Black frost - no ice forms on the plant due to low air humidity and low soil moisture. Named for the color the plant turns.
How Do You Take Care of Outdoor Plants in the Winter?
1. Growing Zone
Selecting plants that grow where you live is the easiest way to prevent winter damage.
Find your hardiness zone at the Nature Hills Growing Zone map and enter your zip code. Your local County Extension Office can pinpoint it further if you are on the edge or in a microclimate. Elevation can also drastically change your growing zone. Knowing the first and last frost dates helps too.
2. Choose Plants For Your Climate
Knowing you have installed plants for your hardiness zone, and then following their sun/shade, soil, and water requirements eliminate worry and staying up late watching the weather or throwing blankets over your prized Roses!
Choosing native plants for your hardiness zone means even less worry and more benefits for you and your environment.
3. Bring Them Inside
Tropicals, subtropicals, or annuals accents need attention because they are not hardy for your area. Exotic bulbs should be cut back, dug up, and stored in late autumn for the winter season. Bulbs like Elephant Ears and Canna Lilies won’t survive when the cold seeps into the ground.
For water gardens, remember to store any plant material such as tropical Water Lilies indoors over the winter.
Exotic in-ground plants, like non-hardy Banana and tropical Hibiscus need protection, and the roots of tender perennials should also be dug and stored for the winter.
Acclimating Your Plants
It’s important to remember that bringing plants indoors for the winter too quickly can actually shock plants too! They need to be acclimated to the indoor environment after being outdoors all growing season.
Citrus and Tropical plants can be kept small and easily adapt to indoor environments. In late summer or early fall, begin moving them to a shaded location so the plant acclimates to moving indoors, and get used to lower light so they can tolerate the change easier.
4. Planting Location Is Important!
Smaller plants may be moved around easily, but larger planters and in-ground plants are another story! Keep them small enough for you to cover them, or plant them in a sheltered position. Preferably near a south or west-facing wall, which absorbs heat all day and radiates it back at night. Other sheltered locations include near fences and large hedges, under large evergreens, in a sunny covered structure, or in a courtyard that creates a microclimate.
5. Covering Your Plants
Snow is protective and insulating for hardy dormant plants. For everything else, or when there is no snow cover, fabric covers trap heat radiating from the soil, keeping plants warmer overnight. Remove them in the morning to prevent condensation from accumulating - leading to mold and mildew issues.
Use stakes or hoops to keep the cover from weighing plants down or blowing in the wind, causing physical damage.
What to Cover Your Plants With
Depending on the size of your in-ground plant, there are several options for covering plants before frost.
Cloches are a garden standard since 1623, and these glass or plastic bell-shaped covers can be placed over smaller plants. Make yours by simply cutting off the bottoms of large, clean plastic bottles or milk jugs. Then embed into the soil over small plants and seedlings to provide localized protection. Remove them during the day.
A cage of chicken wire can be filled with clean leaves, hay, or mulch. This creates an insulated vertical layer that traps the warmth radiating up from the ground.
Temporary frost covers - Keep cold, drying winds, snow, frost, or freezing rain off your plants by using old pillowcases, bedsheets, breathable canvas, burlap, beach towels, cardboard boxes, and overturned trash cans. Fleece blankets or sheets of bubble wrap work great too and there are specialized frost barrier fabrics available.
Black plastic, such as trash bags, can be used so long as they aren’t touching your plants, which is worse than no protection at all. Moisture held against your plants conducts cold right to the leaves.
Old-fashioned incandescent Christmas lights produce small amounts of heat, as does placing warm water-filled jugs beneath the covers.
6. Add a Layer of Arborist Mulch
We at Nature Hills always praise a layer of mulch for all plants in all conditions, all year round! Read about all these benefits in our Garden Blog! A 3-4 inch layer of arborist bark chips, pine straw, compost, clean fallen leaves, hay or straw, newspaper or cardboard, keep plants happier and healthier year-round.
Preventing soil from drying out, adding extra insulation and protection, plus enriching the soil with warmth-sequestering organic material, give plants an edge in extreme conditions. When the cold locks up moisture as snow - it can feel like a drought to a thirsty plant.
7. Winter Watering
Winter watering goes hand in hand with a good layer of mulch. Without moisture at the root zone, plants suffer. While not a problem for deciduous plants with no foliage to support, Evergreens need moisture availability year-round.
Water plants any time in the winter when:
- Been less than 2-inches of snow, snow cover, and/or rainfall for a week
- Temperatures are above freezing for several nights in a row
- New plants that were installed that fall
- Evergreen trees
- Plants receiving the brunt of drying Northern winter winds
Water plants at the roots in the morning because moist soil actually absorbs heat during the day and has an insulating effect.
8. Protecting Outdoor Container Plants
Even if you have native or hardy plants for your growing zone - potted plants have their roots elevated, without the insulation the ground provides. Getting the right container, the right sized container, and one made from the right material is crucial.
Fiberglass planters and solid wood pots provide incredible insulation. For other types of materials, choose one size up and line the interior with styrofoam before filling it with soil. Or, wrap the containers with one of the fabrics listed above, or surround the pots with bales or piles of hay, mulch, compost, or clean leaves.
If the pot is small enough and you have the room, dig a hole in the ground and plant it - pot and all! In spring, you can dig it up, clean it off, and get growing.
Smaller potted plants can easily be moved indoors at night and brought back out for the day. Three-season porches, sheds, or the garage. Save your back with a rolling plant tray.
If you are able to move container plants to an unheated garage or porch area, consider moving these plants to the east side of your house or garage to keep them out of the winter wind and offer some nice protection on their own.
9. Cold-Frames & Greenhouses
When you can’t bring the plant into the house, bring a house to the plant! A cold frame doesn’t have to be expensive either. The simplest are metal hoops straddling your garden beds or rows and covered with clear plastic sheets or bedsheets. Another method is boxing haybales around your plant and covering the top with a sheet of glass, an old window, or a sheet of clear plastic.
Acting like large cloches and are longer-term covers for seedlings, tender plants and perennials, and newly planted annuals (that you got a bit ahead of yourself and planted too early).
More permanent cold frames include a box of wood with a repurposed window pane or sheet of plexiglass or plastic over the top. Hinges allow you to easily lift it during the day and let air in and excess moisture out.
Again, incandescent Christmas lights or jugs of warm water inside raise the temperature a few crucial degrees.
10. Protecting Trees
New trees and others grown in certain climates benefit from trunk wraps. This protects them from frost crack or sunscald - caused by alternating freezing and thawing of moisture under the bark. Protect trunks with burlap or trunk wrap. Just remember to remove it in spring.
New trees need staking to support the trunk and in areas of heavy snowfall and drifting snow. Protect all plants from hungry deer by learning tips here.
For larger plants and trees, knock snow off because it is heavy. Evergreens and tree limbs are at the highest risk of breakage.
Reviving Damaged Plants
If you did get plant damage from the cold, you can try to save it with moderate watering to rehydrate them, but don’t reach for the fertilizer - this may stimulate growth and stress plants further! Prune away dead or damaged material
Keep Things Warm This Winter
An ounce of protection saves you a pound of heartache! Keep Jack Frost from nipping at your plants with a bit of preparedness and head over to Nature Hills #ProPlantTips for more!
Nature Hills Nursery is here to keep your landscape healthy and happy this winter and all year long!
Happy Planting!
