By: Kristi Waterworth
Planting cold-hardy plants may seem like the perfect recipe for success with your landscape, but even these trusty plants can die from the cold if the circumstances are right. Winter death of plants is not an uncommon problem, but by understanding the reasons a plant dies off in freezing temperatures, you’ll be more prepared to get yours through the ice and snow.
You were probably very disappointed to discover that your perennials died over the winter, despite their long-lived nature. Plopping a perennial in the ground isn’t a guaranteed recipe for success, though, especially if you live in an area where it gets very cold and tends to freeze. A couple of different things can go wrong during your plant’s dormancy, including:
If you live somewhere that never freezes, but your plants are still dying over the winter, they may be getting excessively wet during their dormancy. Wet roots that are inactive are highly susceptible to root rot, which quickly works its way into the crown if left unchecked. Look closely at your watering practices if your plants’ warm weather dormancy seems to be a chronic death knell.
Getting your plants to overwinter essentially comes down to choosing plants that are compatible with your climate and location. When you choose plants that are hardy in your climate zone, your chance of success goes up dramatically. These plants have evolved to withstand winter weather similar to yours, meaning they’ve got the right defenses in place, whether that’s a stronger form of antifreeze or a unique way of dealing with desiccating winds.
However, sometimes even the exact right plants will suffer from unusual cold snaps, so make sure to protect all your perennials before the snow starts flying. Apply a layer of organic mulch that’s 2 to 4 inches (5-10 cm.) deep to the root zone of your plants, especially those that were planted in the last year and may not be fully established. Covering younger plants with cardboard boxes when snow or frost are expected can also help them survive an especially trying winter.
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There’s nothing like a defoliated evergreen in January to make us wonder if our shrubs are dead. Too, sometimes it’s tough to tell if a deciduous plant is dead or just playing possum.
Often we choose evergreens because they add winter interest to our gardens. So, when these plants decide to follow the lead of their deciduous cousins and go naked for the winter, our gardens become particularly unappealing. Nandina is one that often turns brown and looks dead after a freeze. But, it probably isn’t actually dead. Yet, sadly, these situations leave many gardeners wondering what in the world they did wrong to kill everything. However, often a winter weary plant isn’t actually dead. And there are some easy tests to know.
For woody outdoor plants, simply scratching the bark may tell you if your plant is dead or alive. In the event that your plant looks dead, but you aren’t sure. Give it a little scratch test.
Late summer or early fall are times for “renovating” your strawberry plants. When you see that your strawberry plants aren’t producing new fruit, it’s time to prepare them for their pre-winter renovation.
The process of renovating your strawberry plant involves cutting it back to just 2 inches (5 cm) high and carrying away the trimmings. This interrupts any disease processes and deprives insects of a winter home.
If you have a small strawberry patch, or you grow your strawberries in containers, you can do the trimming with hedge clippers. If you have a large, flat field, you can use a lawn mower, but you need to make sure the blade is elevated so you leave the crown intact and you don’t take all of the foliage off the plant.
Make sure any plant debris is carried off to the compost pile. Then give your strawberry plants some late-season fertilizer.
Conventional growers can put out one pound of 10-10-10 fertilizer for every 25 plants. Scatter fertilizer pellets over the ground, rake them in gently, and water your plants (preferably with a drip, not with a sprinkler, to prevent a new round of fungal diseases).
If you are growing your strawberry plants organically, this is the time to give them aged compost and foliar mineral sprays.
Either way, fertilize in the late summer or early fall, at least a month before your expected first frost. You don’t want to stimulate tender new growth that would only get nipped by frost. You want the vines and flower buds to have a chance to mature before really cold weather sets in.
Winter care for in-ground strawberry plants
A few light frosts will just send your strawberry plants into dormancy. There is no need to race out to your garden to cover up strawberry plants for frost protection if they have already stopped blooming and bearing strawberries. (If they are still blooming, of course, a thermal blanket — not a sheet of plastic — offers adequate frost protection.)
Winter temperatures much below 15 degrees Fahrenheit (about -10 Celsius), however, will kill the flower buds that the plant needs for next year’s production. It is important to protect the flower buds from winter cold.
Temperatures may be dropping, but that doesn’t mean we have to bid farewell to our herb gardens. Cold-hardy herbs, such as chives, mint, oregano, parsley, sage and thyme, can often survive cold-winter temperatures while continuing to produce flavorful foliage, as long as they are provided with some protection or grown indoors. Even herbs like rosemary that are more cold-sensitive can survive winter using additional methods of protection. Let’s explore different ways we can prolong the herb harvest and enjoy the fresh taste of our favorite herbs throughout the cold of winter.
A glass cloche protects plants in the center of this raised bed in Atlanta.
1. Protect herbs from the cold by placing them in a cold frame or cloche. Covering herbs helps trap the heat that rises from the soil, elevating the temperature inside by several degrees. This can extend the growing season in both fall and spring.
Cold frames are topped with glass panes that slope downward and are situated so they face south. This ensures that the most sunlight will reach the plants inside, creating an environment that is several degrees warmer than outside.
Cloches are a smaller and more portable way to protect plants from the cold. Traditional ones are bell-shaped and made from glass. They can be expensive, but you can make your own by cutting off the bottom of a 1-gallon plastic milk jug or other large plastic container. Place each one over individual herb plants and nestle the bottom inch or two of the cloche into the soil to anchor it.
Herbs 3: The Room Illuminated, original photo on Houzz
2. Add a thick layer of coarse mulch over herbs. Many herbs can grow through the winter under the insulation provided from straw, shredded bark or other coarse mulch. In areas that experience moderate-winter cold, USDA Zone 6 and warmer, herbs will continue to produce some new growth despite some winter cold. Simply pull back the mulch and cut the herbs you need, then cover them back up. While they won’t produce as much new growth as they do in the warm season, you should be able to obtain a small harvest. Don’t worry if a layer of snow falls, as it will provide additional insulation for the herbs below. Once spring arrives, you can turn the mulch into the soil.
3. Pot up herbs and move them into a frost-free greenhouse or sun porch. If you’re growing herbs in the ground, you can transfer them to pots and move them to a protected spot. Select the herbs you want to keep growing over winter, such as chives, oregano, sage and thyme. Cut them back to 1 inch tall and, using a sharp shovel, divide them at their base, making sure to include the roots so each one will fit into the container. Use well-draining planting mix in the containers and plant each herb in a separate pot. They will grow back and you’ll be able to harvest their flavorful leaves until you transplant them back into the garden once spring arrives.
Herbs 4: J M Interiors, original photo on Houzz
4. Grow herbs in front of a sunny window. Herbs can be grown from seed or cuttings and make a great addition to a sunny kitchen window that gets at least six hours of sunlight. If using artificial lighting, 14 hours is usually sufficient. The temperature should range between 60 and 70 degrees Fahrenheit, or 15.6 and 21.1 degrees Celsius, for best results. You can transplant herbs from the garden or begin from scratch by sowing seed.
The rewards of growing herbs indoors throughout the winter are great when the fresh flavor of summer is within arm’s reach. Chives, oregano, parsley and thyme are just a few of the easiest herbs to grow on a sunny windowsill. Use a well-draining planting mix in your container. Water deeply when the top inch of soil is almost completely dry.
5. Extend the life of fresh herbs by putting them in water. Herbs such as basil and mint grow quickly when placed in a container of water for a few weeks. Other herbs that work well in water are sage, oregano and thyme. When placed in water, they begin to produce roots and will grow new leaves. This is a useful way to prolong the harvest, whether you bring in cuttings from the garden or buy fresh herbs at the grocery store.
The process is easy. Simply cut the ends of each stem and put them in a small jar or cup filled with water. Be sure to remove any lower leaves so they won’t be submerged in the water. Place on a sunny windowsill.
The leaves produced indoors will be thinner and slightly less flavorful than those grown outdoors but will still add welcome flavor to your favorite dishes. Refill the water as needed and enjoy the prolonged harvest for several weeks to come.