By Matt Gibson
The weather outside is getting much colder and the layers of clothing under your coat keep growing, one garment at a time. The beautiful days spent in the garden in spring and summer are now a fleeting memory, and unfortunately, your garden plants can’t layer up in clothing like you can to protect themselves against the harsh winter winds. But just because winter is upon us, doesn’t mean that your garden has to die off completely. There are quite a few frost hardy flowers and garden plants that will help keep your garden looking its best all year round.
Will perennials survive winter in pots?
There are a large number of perennials and shrubs that can survive the winter in containers. However, life for a plant in a container is much different from one that is planted outdoors in the ground. Though containers have excellent drainage, the plants they house depend more solely on you for providing nutrients and adequate hydration. Containers can limit the size that a plant will grow because they have limited space in which the root system of plants can spread out and grow into. Containers also fail to insulate a plant’s root system adequately from winter temperatures.
Generally speaking, if your plant is hardy to two zones colder than the area that you are in, it will be a good candidate for being able to survive the winter in a container in your area. There are some exceptions to that rule, and certain plants are better able to survive in containers through the winter than others. Click here to read about 10 plants that are well suited to surviving the winter in a container.
How do you protect perennials in winter?
Mulching is one of the easiest and best ways to defend sensitive plants against harsh winters. Use an organic material when mulching to help improve soil quality as the mulch starts to decompose throughout the upcoming growing season. As the organic mulch breaks down, it will release vital nutrients back into the earth, enhancing the quality of your garden soil in the process. In the fall, rake back old layers of mulch from the base of plants in your garden beds, spreading a new three inch layer around them. Leave about one half of an inch of space clear around the stem of your plants to discourage rot issues and to allow for proper air circulation.
White washing tender tree trunks or wrapping them with a bit of burlap can help fight off winter sunscald. Build a 12 to 18 inch mound of soil up around the base of roses to protect the crown from winter freezes. New tender foliage that pops up on your bushes and shrubs should be treated with an anti-desiccant to help defend them from cold winds and harsh winter sun.
A thick layer, at least six to eight inches deep, consisting of wood chips or straw, should be added to the top of flower beds to protect in-ground perennials during the winter. Screens or frames can be built and placed on the southwest side to help shield tender plants from harsh winds.
Keep a dolly on hand for potted plants so that you can easily transport them to a sheltered location, or indoors when temperatures suddenly drop low. Watering potted plants that you plan to leave outside just before a freeze can be a mistake, unlike watering garden beds before a freeze, which is highly recommended, as high moisture levels inside smaller pots can lead to quick freeze threats. Some plants can benefit from a cage, structure, or cold frame built up around them for extra protection. A chicken wire cage filled with straw for insulation, can be used as a cold barrier for tree trunks.
Wrap tall shrubs (like arborvitae) with twine to bring the limbs in closer together so that they don’t break and splay if snow builds up on them. Prop up horizontal limbs with stakes to protect against breakage from the weight of snow that may build up on them. Sometimes, winter weather protection can be as simple as laying out an old sheet or blanket across the top of garden beds to help insulate the plants underneath, providing just enough warmth to keep them alive during a freeze. Frost barrier fabric is great for fruit trees in the spring. Burlap can also be used as a plant cover during freezes.
All covers should be removed during the daytime so that plants can continue to get sun, then replaced when the sun goes down to shield the plants underneath from harsh evening weather. For the most effective results, covers placed over garden beds should reach all the way to the root zone. Ties or stakes can be used to hold them in place but never bind them to plants with twine or rope to avoid injuring the plants below.
How cold is too cold for flowers to be outside?
Winter is typically quite hard on flowers. Some flowers can endure lower temperatures than others. To be on the safe side, take measures to protect all of your plants when temperatures start to drop in the winter.
Should you water perennials before a freeze?
Yes, you should water perennials in the garden bed before a freeze, as wet soil holds more heat than dry soil, which in turn, will protect the roots from freeze damage. However, caution should be taken when watering potted plants before a freeze if you plan on leaving them outdoors during the cold front, as potted plants don’t have a large surface area, and are susceptible to quick freezes if the soil is too moist.
What perennials can I leave outside in winter?
Hostas – Hardy to zone three, these shade loving perennials can survive some pretty tough weather with only a light blanket at night for protection.
Pansies – In zones six and up, pansies should survive the entire winter, and provide plenty of blooms during that time as well. Blooms can survive cold snaps and tolerate single digit weather for a couple of hours at a time.
Kale – Once hardened by cool night temperatures, Kale plants can survive most winters.
Primrose – There are a few species of primrose that bloom in late winter. Sow these seeds outdoors from January to March.
Cypress Topiary – Water sparingly to avoid rot issues, and place in an area that receives morning sun and afternoon shade.
Cyclamen – A prolific fall bloomer, cyclamen displays vibrant foliage from winter to spring.
Peony – Peonies actually need cold weather to bloom and in most climates, mulching will actually inhibit blooming. If given the right growing environment, peonies will live for many years before needing to be replaced.
Wheeler’s Dwarf Japanese Mock Orange – Normally grown as a groundcover, this plant can survive the harshest winters with no protection.
Siberian Iris – Cold winters are no match for the Siberian iris. Hardy to zone three, this iris is low maintenance, animal and pest-resistant, and tolerant of both wet and dry soil conditions.
American Mountain Ash – This plant is a cold-weather lover hardy to zones three through six. Requires well-draining soil and consistent moisture.
Coneflower (Echinacea) – Most varieties are hardy to zone three. Cut down stems and add three to four inches of mulch to help insulate them during the winter.
Catmint – Though catmint stops blooming at the first fall frosts, the plant itself stands up to winter with ease, displaying lush silver foliage through the cold months of the year.
Coral Bells (Heuchera) – Prone to heaving in the wintertime, so add three to four inches of mulch in the fall before temperatures drop into low ranges. Hardy to zones three through nine.
Viola – Known to keep blooming, even in warm weather, this winter hardy flower will keep your winter garden flush with color in zones five to 10.
Swiss Chard – Though chard is not as hardy as fellow leafy greens like collards and kale, it is frost-hardy enough to stand up to the first and last frosts of the season.
Fastigiata Spruce – Hardy in zones two through seven, this freeze-proof dwarf tree is also drought and heat tolerant once established.
Cabbage – One of the most popular winter annuals, cabbage can survive most cold winters once they get a taste for cold winter nights.
Thread-Branch Cypress – The golden-yellow leaves of the thread-branch cypress are great for adding texture to your winter garden. Requires full sunlight to thrive. Keep it contained in a pot or plant it in the ground to watch it grow as high as eight feet tall.
Lily of the Valley – This is one tough plant, and can be borderline invasive if not maintained. Hardy to zones two through seven, lily of the valley is freeze proof and can survive in practically any soil or climate.
Blue Spruce – Popularly grown as Christmas tree alternatives, the blue spruce is a winter-hardy dwarf tree that needs a lot of water. Place a sponge over the drainage hole of its large containers to help improve water retention.
Japanese Yew – This plant can be grown as a tree or a groundcover and is known for its ability to survive especially cold winters.
Collards – These delicious leafy greens tolerate freezing in zones 8 and up.
Ligustrum – Thrives in full sun and partial shade, ligustrum’s popularity as an ornamental plant has spread across the Southwestern US states.
English Boxwood – Perfect for containers, this low maintenance topiary only requires water twice per week and full sunlight exposure.
Want to learn more about growing perennials in the winter?
Ambius covers Plants That Survive the Winter
Better Homes & Gardens covers Perennials That Can Survive Harsh Winters
Bob Vila covers Liven Up Winter Porch with Cold-Loving Plants
Fine Gardening covers 10 Plants for Year Round Containers
Gardening Know How covers Protecting Winter Plants
HGTV covers 10 Winter Friendly Plants for Outdoor Spaces
HGTV covers Freeze Proof Plants
SFGate Homeguides covers Prevent Frost Damage to Potted Plants
Proven Winners covers Overwintering Potted Perennials and Shrubs