Many plants that northern gardeners grow as annuals are, in fact, tender perennials. That list includes vegetables such as peppers and artichokes, and flowers like snapdragons and impatiens, fruits like figs, and favourite herbs such as rosemary and marjoram. Let’s look at some ways to keep them growing for many years!
What is a Tender Perennial?
A perennial is a plant that does not die after it has completed a season of blooming and setting seed, but will come back year after year. Many perennials are herbaceous, meaning that they die back to the ground in winter. Woody perennials may lose their leaves but otherwise maintain their above-ground shape all year.
Tender perennials are plants that cannot survive freezing temperatures at all, or only for brief periods. In cold climates, they need to be grown as annuals or protected in some way through the winter months. And that’s what we’re here to discuss!
How Do You Protect a Tender Perennial to Live Through Winter?
Mulching can be an effective method of protecting herbaceous perennials that are borderline in your growing zone. For instance, if you garden in Zone 5 and are growing perennial that is only hardy to Zone 6 or 7, you can probably ensure its survival through a normal winter by covering it with a thick layer of straw or leaves.
Cut the foliage back to the ground, and cover the crown with at least 3 inches (7.5 cm) of straw or leaves. To keep things looking neat and prevent the mulch from blowing away, you can surround the crown with a chicken wire collar, or cover the whole thing with an overturned terracotta pot.
If a plant does not naturally die back to the ground in winter, mulching will not protect the exposed parts, so once you’ve spread the mulch around the base, you will need to provide additional insulation to keep it safe through the winter months. For plants such as figs, the best way to do this is by driving a few stakes as high as the plant into the ground about a foot away from the base and wrapping a length of burlap or another breathable material around the perimeter.
Then, loosely fill the interior with shredded leaves or straw, right up to the top. Finish it off with an overturned pail or a tarp on the top of the structure to keep things dry over the winter.
For tender perennials such as snapdragons, moving them into an unheated greenhouse is often enough protection to get them through the cold months, but you do need to take a few precautions.
Your greenhouse should have planting beds to transplant them into, as they will need the insulation of the surrounding soil. It’s also a good idea to cover them with an insulating blanket on really cold nights, and on sunny days you will have to vent off the hot air, as even when it’s well below freezing, inside the greenhouse temperatures can reach summer highs! It’s worth the trouble, however, when you can keep beautiful flower plants going strong year after year.
Bringing in Your Potted Plants
I have a jalapeno pepper plant that is currently in its fifth year because I bring it into my basement every fall. A couple of times I let it go dormant after cutting it back, but the last two years I’ve kept it under grow lights all winter, and I was harvesting peppers in January!
You can also bring in herbs such as rosemary, flowers such as impatiens and geraniums, as well as small fig trees, and then bring them back outside in late spring when all danger of frost has passed.
Flower plants such as dahlias, gladioli, and canna lilies are easy to store as tubers for the winter. Once the first frost has blackened the plants, cut them down to the ground, and carefully dig up the roots. Let them dry for a few days, and then store them in paper bags, vermiculite, or even some kitty litter. Check them every month or so and remove any tubers that may have rotted to keep the rest in good shape, and plant them out in late spring.
If you don’t have room to keep whole plants indoors through the winter, why not take cuttings instead? You can do this with peppers, tomatoes, sweet potatoes, snapdragons, impatiens, geraniums, petunias, and a whole host of other tender perennials. Cut young stems just below a leaf node, and either stick them in a damp growing medium or into a jar of water until roots form, when you can plant them in small pots. This way, you save the cost of buying new plants next spring, and will see flowers or fruits faster than when you start from seed.
Do You Need to Protect a Tender Perennial from a Frost?
Not all tender perennials need to be protected from light frosts in spring and fall, but others will be damaged by even the slightest freeze. For instance, snapdragons will weather even moderately cold weather, while petunias and peppers need protection whenever temperatures are predicted to dip close to freezing.
Does a Tender Perennial Need to Be Watered During Winter?
If you are keeping tender perennials protected in a planting bed over the winter, they won’t need to be watered, as they will have gone dormant until spring. In an unheated greenhouse they should also be okay, although if things get really dry you might need to water occasionally. If you’ve potted plants up and kept them actively growing indoors, water them as you would any indoor plants.
You may also need to mist them to keep humidity levels up for plants such as rosemary. If you’ve let potted plants go dormant indoors, water them no more than once a month.
How Do You Prepare Your Tender Perennial for Spring?
It’s important not to jump the gun in spring and expose tender perennials to low temperatures. If you’re bringing plants outdoors after a winter inside, wait until things don’t get much cooler than 50°F (10°C) overnight, as colder weather can set back their growth. You will also need to acclimatize them to outdoor light levels gradually. Start them off in shady spots, exposing them to stronger light over a period of a couple of weeks. Keep them well-watered.
If you’ve sheltered plants outdoors through the winter, don’t uncover them until things start to warm up and the ground is fully thawed.
Buying new plants every year can get expensive, so if you have the chance to over-winter tender perennials, you’re not only going to save money, but also will start the spring off with bigger, better plants that will produce flowers and food faster!
Read our related winter gardening posts:
- 25 Winter Backyard Ideas for All Budgets
- Can You Trim Bushes in the Winter?
- How to Prepare Your Garden for Winter | 8 Tips
- How to Improve Garden Soil Over the Winter?
Janice is a retired High School teacher who is spending her leisure years keeping busy with all sorts of projects. Aside from freelance writing, she’s an enthusiastic amateur chef, home wine maker, and tends a large raised-bed vegetable garden, while at the same time running a Bed & Breakfast.