Perennial bushes and trees will drop their leaves, but the woody stalks and branches will remain. These woody parts can survive the cold and the underground roots and bulbs will stay alive, but the leaves dropping is a result of the nutrients in the plant moving from the leaves to be stored in the stem and roots.
2. Perennials and shrubs that are in your zone or one colder can be overwintered in an unheated garage, buried in the ground, or transplanted. 3. Perennials and shrubs in containers will need water through the winter but should not be kept wet.
Overwintering Techniques
The general consensus seems to be that the best way to overwinter containerized perennials is to take the entire pot and bury it in the ground. This way, the roots are protected like they would be if the plants were actually planted in the garden.
Plants and perennials that require additional protection to survive your winter will need a deep layer of mulch added by mid November or later, when the ground is beginning to freeze. Do NOT add deep mulch too early or your plants will not be slowly exposed to colder temperatures, allowing them to acclimate for winter.
A hard freeze in May is not uncommon for some areas and can kill tender perennials. Hardy plants such as daylilies, hosta, peonies, lily-of-the-valley will survive a late spring frost, but they will be out of commission until warmer weather returns.
The newly emerged growth of most perennials can tolerate temperatures in the low 30s and upper 20s Fahrenheit. Freeze damage may occur if temperatures drop into the lower 20s or teens. Most well-established perennials that have been damaged by freezing temperatures should survive.
Thoroughly Water plants if it's not going to rain before the freezing temperatures arrive. It may sound illogical. However, a moist ground stays warmer than dry soil. Watering the night before the freeze comes will insulate the root structure of the grass and plants and decreases the potential for cold injury.
However, there are cultivated plants which are more susceptible to problems if the old foliage and dying stems are left to rot. Diseases can overwinter in dead foliage, as can slugs and other pests. Old stems can also get battered about by fall and winter winds, which will damage the plant's crown and roots.
The best time to mulch perennials is after the top 1-2 inches of soil has frozen. The mulch provides insulation, keeping the soil consistently cool through winter. Loose organic mulch, such as shredded leaves, bark chips, pine needles, and straw, is a good choice for helping perennials survive winter.
Hostas, daylilies, black-eyed Susan and many other common perennials need little more than a trim back and a bit of protection from a layer of mulch to survive.
Heated Greenhouses with Roll-up Sides
This method requires minimal fuel and results in very few plant losses. To use this method, perennial houses are heated to 50°F until all of the plants are well rooted, then the temperature is slowly decreased to 35°F so the plants will vernalize and flower in the spring.
Many perennial plants die back as fall moves into winter. Preparing perennials for winter cold often starts with pruning back dead leaves and stems. The foliage of these plants, including peonies, lilies, hostas, and coreopsis, blacken after the freeze.
At any time during the warm season it is okay to cut back dead or ugly foliage. When winter has arrived, and your perennials have either died back or stopped growing, you can remove all dead foliage. Then apply an inch or two of compost or mulch around plants. Leaves work great for mulch as well.
Perennials, on the other hand, live for three or more growing seasons. They are less work than annuals because they grow back each year from roots that go dormant in the winter. They will be around from year to year, so they put their energy into growing strong roots instead of growing lots of flowers like annuals do.
Digging Up Root Ball on Perennial Plant
When dividing or moving a perennial, dig up as much of the rootball as you can. Go outside the plant's drip line by a few inches and plunge your shovel in. Photo by: Image courtesy of Johnny's Selected Seeds. Image courtesy of Johnny's Selected Seeds.
Some perennials, like hostas, peonies and daylilies, need to be pruned in fall to avoid winter damage. Plants like these should be pruned after the first few frosts in late fall or early winter. Other perennials like mums and coneflowers are better off being pruned in spring just before new growth comes in.
Early spring and fall care are best times for transplanting. Then the weather is cooler and the plants are not using as much water. “However, don't move or transplant perennials while they are in bloom,” he says. “As a general rule, wait a few weeks after they bloom before moving.
The good news is that hostas, also known as plantain lilies, are tough and forgiving plants. Even if you forget to prune them at a certain time or you neglect to prune them at all, they'll still survive just fine, even if they don't look their best.
But when should hostas be cut back? Hostas should be cut back in late fall. Healthy hosta leaves can be left on the plant in early fall to capture much-needed energy, but all leaves should be trimmed off after the first frost to deter slugs and other pests from making your hosta their winter home.
The process of trimming back plants is the same for nearly all perennials. Begin by cutting the plant back to 3 to 5 inches above the soil line. Using a sharp pair of pruners or hedge trimmers, cut off all of the foliage and stems. Cut the plants down to within three to five inches of the soil line.
Pruning Perennials – General Pruning
In early spring, old foliage should be removed from most plants. Many spring blooming perennials should be pruned just after the blossoms fade. Perennial plants which bloom during summer and fall should be pruned in spring to create bushier, more floriferous plants.
Farmers spray water before an overnight freeze because water produces latent heat when it freezes. The sprayed water on the surface of the plant will be converted to ice, and the heat trapped in it will insulate the plant from the cold environment.
Cover Plants – Protect plants from all but the hardest freeze (28°F for five hours) by covering them with sheets, towels, blankets, cardboard or a tarp. You can also invert baskets, coolers or any container with a solid bottom over plants. Cover plants before dark to trap warmer air.