In the north the snow is already beginning to swirl, and the first heavy falls are not far away. New gardeners are often surprised to see that their evergreens can look fine all winter, through ice and snow, but as soon as the warmer weather comes back in spring the foliage begins to brown. Soon it is clear they are dead, or at least have lost branches. So what went wrong? And even more important, what can be done to prevent this happening? Let’s look at the reasons for this damage, and some simple tips on how to prevent it.
- Water late in fall – by soaking the ground just before freeze-up, you will keep some free water available, especially deeper in the ground
- Use a mulch – especially if there is no snow cover, a mulch will stop the cold penetrating deeply into the ground, and trap the natural warmth of your soil
- Wrap your plants in netting – netting is almost as effective as burlap, not unsightly, cannot harm your plants in spring, and hold Christmas lights too!
- Pile up the snow – snow is an excellent insulator, so don’t remove it from around your evergreens
- Avoid late planting – planting evergreens late in fall makes them more vulnerable. So start planning now, and pick up early-spring bargains – because that is the ideal planting season in cold regions
Why Do Evergreens Die in Winter?
Unlike deciduous trees and shrubs, which lose their leaves in fall and pass the winter with their buds tightly covered, evergreens keep their leaves all winter. This can be very helpful to them, as they can continue to produce some sugars on a sunny day, even with the temperature below freezing. But like everything, there is a down-side too. Even though the leaves of evergreens are often tiny, grip the stems tightly, and have thick coverings, they must still open a little to the air to stay alive, and to bring in carbon dioxide. This process, called ‘transpiration’, also releases water, and the air in winter is very dry, so a lot of water can escape.
So while your deciduous shrubs are happy sleeping, and losing very, very little water, your evergreens steadily release it into the air. This water has to be replaced, and of course it is the job of the roots to draw it out of the soil to do that. Here is where the winter problems begin. Even before we see the first snow, in many places the ground has begun to freeze. As winter progresses, that freezing can penetrate one, two, and even three or more feet down into the soil. As the soil freezes, so does the water in it. You can immediately imagine the problem for your evergreens – they are sucking on a block of ice – which is not the easiest way to get a drink!
When not enough water is being drawn up, the leaves begin to dry. Soon, even though they still look green, they have become so dry that they have been irreversibly damaged. When spring returns they cannot recover, and the warmer weather finished off the drying process, leaving them crisp and brown. This damage is not caused directly by cold – trees that can happily survive minus 30 degrees can be damaged at minus 10, if they dry out. So this kind of injury is called ‘winter burn’, to distinguish it from the damage to tender plants caused by freezing.
How to Protect Your Plants from Winter Burn
Winter Burn is especially a problem with new plants, or ones you have recently moved. They have limited roots, and those roots don’t go down very far, so as soon as the soil around them freezes, they can no longer take up water. So although you can see this problem with older plants, once your evergreens have been in the ground for a few years they will usually go through winter just fine. These tips I am about to give you are most important for younger, newly-planted evergreens.
- Soak the root area late in fall, just before the ground freezes. It takes a lot of cold to freeze water, so the more of it there is, the better the chances that it will not all freeze. Some water deeper down will still be liquid, and the roots of your evergreens will be able to draw it up easily. So no winter burn. Simple as this is, soaking your evergreens is the single best thing you can do to protect them for winter. Just leave a hose trickling gently for a couple of hours, until the ground is thoroughly soaked.
- Mulch around your trees, using any kind of coarse material. Bark chips, wood fiber, compost or manure – these are all good insulators. They are much more effective than stones or gravel, and as they decay they feed your plants too. If you go out after the ground has frozen, and look underneath the mulch, you will often be amazed to see that the ground is still soft. Cover a large area around your plants, so that all the roots are protected, but keep mulch away from the trunk, and be careful not to bury the foliage.
- Wrap your trees in netting. You might see old-time gardeners wrapping sheets of burlap around their evergreen trees, but there is a better solution than this ugly method. Wrapping works because it reduces wind flow through the plants, so they lose less water. You get almost as much benefit from using netting instead, and it doesn’t even show from a few yards away. Find some black or dark-green net, because it is the most invisible, and wrap carefully, pulling the branches together, but not wrapping tightly. Follow the natural shape, and hide the ties at the back, if you can. Netting also protects your trees from being damaged by snow, so it serves a double purpose.
- When clearing snow, leave it around the roots. Don’t blow the snow away from around your evergreens, although brushing it off the foliage is a good idea, to prevent breakage. Snow is a great insulator, so it helps to keep the soil warm and so less likely to freeze hard.
- Spring planting is better than late fall. Although early fall is a terrific time to plant evergreens, you need a window of a few weeks before freeze-up, to give the roots some time to establish. If you live in a very cold place, spring planting is better than putting them in in late October or November. Planted in April or May they will have the summer and early fall to become well established. If you are thinking of putting in some evergreens, put in your order now for spring delivery, and you will get the best-quality new material from the start of the season.