Cold-Hardy Perennials: Preventing Frost Damage

hens and chicks cold hardy perennial

Preventing Frost Damage in Springtime

Spring in the western Rocky Mountains has nothing to do with a calendar but is dictated by the weather. Just when gardeners and plants are suckered by warmer weather, Jack Frost pays us a late-season visit and frost damage wreaks havoc on tender new perennials’ growth. Plants are at their most venerable period as they break spring dormancy. The freezing temperatures usually result in temporary leaf damage. Most perennials will outgrow the white, bleached leaf tips, but if they don’t, the damaged portions should be pruned off. This isn’t lethal to the plant but it is lethal to the upcoming season’s flowers because the flower buds will most likely also get pruned from the plant. Frost injures plants by causing ice crystals in the plant cells, thus disrupting any movement of liquids. Here are three tips for protecting your plants from frost damage, and I’ll address each in more detail:

1. Select perennials hardy to your planting area.
2. Use defensive measures to avoid frost damage
3. Don’t get overanxious!

Choose Frost-Tolerant Perennials

Frost-Tolerant Perennials usually fall into one of 3 categories: Alpine or groundcovers, drought-tolerant or evergreen perennials, or sometimes a combination of two or three. Helleborus is an excellent example of a perennial that fits into all three categories. Here are several others:

Ajuga evergreen groundcover perennial - prevent frost damage
Ajuga is an outstanding evergreen groundcover for shade and admired for its distinctive variegated foliage.
aubrieta, rock cress and spring bulbs
Alpines like Aubrieta are so adapted to mountain up and down elevations and temperatures that they are rarely bothered by anything. Spring bulbs are noted for their weatherproofing or perhaps they have a canny instinct about when to push up through the ground.
cold hardy Dianthus, 'Frosty Fire'
Dianthus stays evergreen and is drought-tolerant, so its foliage is never damaged by winter snow or frost. The flowers are protected because they don’t bloom until June. Ironically, this Dianthus is called ‘Frosty Fire’. Photo: Walters Gardens

 

 

Blue Festicua evergreen perennial grass
Blue Festicua stays somewhat evergreen and is never bothered by frost or much of anything else.
pulsatilla Lenton Rose cold hardy perennial
Pulsatilla’s other name is Lenton Rose. It resembles a rose and starts blooming during Lent, (the forty days of moderation before Easter). The plant is small until its blooming is completed, then the foliage will grow to about fifteen inches of green lace.
hens and chicks cold hardy perennial
Hens and Chicks are hardy, drought tolerant, evergreen who never falter at the weather unless the ground is too wet. If so, they may rot in a freeze situation.
Thyme, Cold-hardy Perennial
Thyme’s foliage stays attractive all four seasons. This tough perennial is an Alpine, a drought tolerant and an evergreen plant.
cold-hardy yucca perennial
Yucca is not only drought tolerant, but stays evergreen and always has gorgeous waxy foliage that has its own antifreeze right between the front and back of its leaves.
  1. Defensive Measures to Avoid Frost Damage

    1. A layer of compost or mulch over the perennials not only slows down the breaking of dormancy time but holds in water for wet soil helps trap heat.

  2. 2. Cover plants with frost cloth, sheets or blankets. Make sure the covering is not touching the plants. Plastic is not an adequate cover.
  3. 3. Build a cold frame.
  4. 4. Supply a heat source by installing an electric light bulb or even Christmas decorations that can be turned on at night or if the weather takes a turn for the worse.
  5. Our first cold frame was made of windows our neighbors removed for new replacements. This cold frame is totally portable taking maybe twenty-minutes to put up and another twenty-minute to take down when the weather settles. We use this cold frame for our potted cannas and dahlias so we can get a head start on growing them.
    Our first cold frame was made of windows our neighbors removed for new replacements. This cold frame is totally portable taking maybe twenty-minutes to put up and another twenty-minute to take down when the weather settles. We use this cold frame for our potted cannas and dahlias so we can get a head start on growing them.
  6. Don’t Get Over-Anxious!

Box stores are famous for their early tempting displays of flowers in full bloom. Remember, if a perennial is in full bloom, out of season, it has been greenhouse grown and has probably enjoyed a diet of daily fertilizer. These perennials have no defense against a frost or hard freeze and if planted too early, may not survive. Wait until the weather makes it fun to be outside, digging in the dirt before planting perennials.

More Plant Protection Ideas

This video, provided by GrowVeg, shows several methods for protecting plants from frost. The concepts apply to both vegetable gardens and perennial gardens. (This video includes information about using a garden planning software. Stop the video at 4:30 if you are not interested in this information). You can find dozens of videos on YouTube that explain methods for building your own cold frames.

More about Nedra Secrist