Brian Minter: Hard lessons to learn from winter cold snap

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We are now beginning to see the effects of our intense cold spell in January. It was far more devastating to some plants than others simply because the prior very mild El Nino weather pattern caused dormancy to end earlier, and many plants were already starting to set bud.

My concern is that many folks will begin taking plants out because they look like they are dead, which in some cases they are, however many are actually still alive but covered with burnt leaves. When the growing season begins, many of these winter-burned plants will bounce back.

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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 run of four or five days with temperatures in the 15 C to 20 C range will reveal whether or not your plants have survived. Once it gets warm, severely damaged plants will simply not leaf out and they can be removed and replaced.

Plants in containers were the greatest victims. Any plant out of the ground loses at least one zone of hardiness because the roots do not have adequate soil protection. The simple solution going forward is to wrap your containers and the plants with a true insulating cloth like N-sulate which, depending upon the grade of insulation, can make up to a 10 C difference. Burlap, which many folks 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 spells and it makes all the difference in their survival.

Broad-leafed plants, especially those exposed to outflow winds, were perhaps the hardest hit. Rhododendrons are classified in 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 leaf size, the more resilient the plant will be to both sun and cold if you’re in an unprotected area.

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

Fortunately, rhodos send new growth out of old, hard wood, so badly burnt plants can be pruned back below the damaged leaves, but stay above the new buds just forming on the woody stems. Since many plants have been allowed to grow quite large over time, it might be advantageous to prune harder and bring the plants back to a size that better conforms to your landscape. Keep in mind, the harder you prune into the old wood, the longer it takes to bring them back into a nice-looking plant. It may also take two seasons of growth to return your rhodos to a blooming state, so you’ll have to be patient.

Once all your broad-leafed shrubs like pieris japonicas, skimmias, leucothoes, and evergreen Japanese azaleas have lots of new growth showing, you’re safe to prune them back and properly shape them. Let your azaleas bloom first, however, then prune. Cleaning up the dead leaves and small branches will renew the plants.

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I’m most worried about roses, especially the budded varieties. If traditional floribundas and hybrid teas did not have the bud unions mulched or protected, especially in exposed, windy areas, there’s a good chance they may not make it. Again, warmer weather will determine their 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 likely will not survive.

For the most part shrub roses should be fine. They are the hardiest roses since they are on their own roots and can send out new growth just below ground level.

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

Most flowering shrubs are fairly hardy and when their new growth appears, simply prune back any dead wood. Remember to let all early spring flowering varieties bloom first, only then can you prune back to ensure flowers for next year.

Many ground covers, like cotoneaster, salal and thyme will have many brittle leaves if they were subjected to the cold winter winds, but if they are well established, they should come back nicely in the warmth of spring. Some tidying will be required once you see the new growth.

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Evergreen perennials, like euphorbias, hellebores, and evergreen grasses took quite a beating as well. Simply remove the blackened foliage of the hellebores and new growth will soon appear. Wait for that new growth to begin and then you can prune appropriately.

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

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