Brian Minter: Hard lessons to learn from winter cold snap

Save as much as you can and don’t give up on your plants until the good weather ahead determines their fate.

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We are now starting to see the effects of our intense cold snap in January. It was much more devastating for some plants than others simply because the previous very mild El Niño weather pattern caused dormancy to end earlier and many plants were already beginning to sprout.

My concern is that many people will start pulling out plants because they look dead, which in some cases they are, however many are actually still alive but covered in burnt leaves. When the growing season begins, many of these winter-burned plants will recover.

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The true test of survival is a few days of warm weather. This may not happen until late March or early April, but a period of four or five days with temperatures in the 15C to 20C range will reveal whether or not your plants have survived. Once it gets hot, severely damaged plants will simply not leaf out and can be removed and replaced.

Plants in containers were the biggest victims. Any plant out of the ground loses at least one hardiness zone because the roots do not have adequate protection from the soil. The simplest solution is to wrap containers and plants with a real insulating fabric such as N-sulate which, depending on the degree of insulation, can make a difference of up to 10 C. Hessian, which many people use, has little insulating effect against the cold, but helps mitigate the effects of cold winter winds.

As a precaution, we wrap all our deciduous trees and shrubs with N-sulate during severe cold snaps and it makes a difference in their survival.

Broadleaf plants, especially those exposed to outflow winds, were perhaps the most affected. Rhododendrons are classified into three hardiness categories: H1, H2 and H3. In the Lower Mainland, H1 and H2 varieties are very hardy, but the more tender H3 varieties, which are equivalent to a Zone 7 rating, are more easily damaged by cold winds. The other rule of thumb I use is leaf size; The smaller the size of the leaves, the more resistant the plant will be to both the sun and the cold if you are in an unprotected area.

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If last summer’s intense heat did not burn the leaves of your rhodes, exposure to prolonged cold certainly fried the leaves of many of the more tender varieties. I know they look horrible, but leave them alone until they bloom and new foliage growth begins. You can prune once you see the new green shoots.

Warmer weather will determine the viability of your garden plants. Photo by Brian Minter

Fortunately, rhodes generate new shoots from old, hard wood, so badly burned plants can be pruned below the damaged leaves, but remain above the new shoots forming on the woody stems. Since many plants have been allowed to grow quite large over time, it may be advantageous to prune harder and return the plants to a size that better suits your landscape. Keep in mind that the harder you prune old wood, the longer it will take to turn it back into a good-looking plant. It may also take two growing seasons for your rhodes to bloom again, so you will need to be patient.

Once all of your broadleaf shrubs, such as pieris japonicas, skimmias, leucothoes, and evergreen Japanese azaleas, are showing lots of new growth, you can safely prune them and shape them appropriately. However, let the azaleas bloom first and then prune them. Clearing dead leaves and small branches will renew the plants.

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I’m most concerned about roses, especially varieties with buds. If traditional floribundas and hybrid teas did not have their bud unions mulched or protected, especially in exposed and windy areas, they would most likely not make it. Again, warmer weather will determine its viability. Even if you have just a few green shoots above the bud union, you can save the rose.

Tree roses were particularly vulnerable as their bud union is at the top of the long stem and, if they had no protection, they probably would not survive.

For the most part, bush roses should be fine. They are the hardiest roses, as they are on their own roots and can produce new shoots just below ground level.

The lesson here is to protect all your roses with mulch every November and wrap them if necessary.

Most flowering shrubs are quite hardy and when their new growth appears, simply prune away the dead wood. Remember to let all early spring flowering varieties flower first, only then can you prune again to ensure they flower for next year.

Many ground covers, such as cotoneaster, salal and thyme, will have many brittle leaves if they were exposed to the cold winds of winter, but if they are well established, they should regrow well in the warmth of spring. Some cleaning will need to be done once you see the new growth.

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Evergreen perennials such as euphorbias, hellebores and evergreen grasses also took a big beating. Simply remove blackened foliage from hellebores and new growth will soon appear. Wait for that new growth to start and then you can prune properly.

This cold snap was one of the worst I have ever seen due to such sudden, intense cold after what had been a very mild winter. He taught us all some important gardening lessons, and over time, these experiences will continue to expand our gardening wisdom. In the meantime, save what you can and don’t give up on your plants until the next warm weather determines their fate.

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