Anti-desiccant Sprays – a Good Idea?

The arrival of winter can be a time of concern for growers of evergreens. Unlike deciduous plants, our evergreens remain, well, evergreen, so their foliage is exposed to the cold, harsh winds of winter, especially during storms. When spring comes, and we find brown, dead patches and branches, this is often put down to low temperature, but that is not really true. ‘Winter-burn’, or ‘desiccation injury’, as this condition is known, is caused not the branches becoming cold – evergreens are well adapted to low temperature, as we can see when climbing mountains or heading north. As we enter colder and colder areas, it is the evergreens, like spruce or fir, that persist, as the deciduous trees disappear.

So if it is not cold, what exactly is the problem? Put simply, there is an imbalance between the amount of water lost from the foliage, and the amount absorbed at the roots. A lack of water in the leaves, aggravated by dry air and a strong wind, causes the foliage to dry out, and of course it dies. Where cold comes in is in the roots. Although the soil may be wet, once that water freezes, it cannot be taken up by plants. In a nutshell, this is the fundamental problem, and why you may have a sad face in spring when you see your plants.

Preventing Winter-burn – Some Tips

What is a gardener to do? The traditional approach is to do one or all of these four things:

  • Water your evergreens heavily just before freeze-up. This will slow down hard freezing, and hopefully leave some free water available for your plants. This should always be done, no matter what additional protection you provide.
  • Mulch the ground over the roots. The deeper levels of the soil don’t freeze, and they contain a lot of warmth. A mulch will insulate the roots, keeping the cold away and allowing that deep warmth to rise and prevent the soil from freezing. Even if the ground does eventually freeze in the depths of winter, it will be for a shorter time, so there is less chance of the foliage losing a lot of water, and a better chance it will stay alive.
  • Wrap the trees in burlap to slow down the wind. Reducing wind flow over and through your plants reduces the rate of water loss, and often prevents winter burn. Wrapping can have a secondary benefit in preventing salt-spray damage, but only if there is a space between the burlap and the trees. If not, the salty water will be held against the foliage, and the problem may be magnified.
  • Wrap trees in netting. This has the advantage of being much less visible, and has been shown to be almost as effective as burlap. It is especially useful for specimens, but even a hedge could be netting, with a little effort.

An Alternative Approach – Anti-desiccant Sprays

These methods are fairly well-known, and in fact we have already discussed them in early posts. But there is another, less used method that may be not only the easiest, but the most effective approach to take. This is the coating of the foliage in materials that slow-down or prevent water loss from the leaves, and so protects them very effectively from winter-burn.

These anti-desiccants have been used by professionals for a couple of decades, but they have not been adopted much by home gardeners. This is a pity. They have lots of other uses around the garden, that we will look at later. Here though, we are primarily interested in their use specifically for evergreens, especially in the first winter or two after planting. These are the times when plants are most susceptible to winter-burn. Once the roots are well-established, they are more efficient at keeping up a sufficient water supply to the roots, and well-established plants are not likely to suffer from winter-burn. A heavy watering and some mulch is all they need.

What Are Anti-desiccants?

There are several products available, with names such as Wilt-Pruf, Wilt-Stop, and ArborGuard. All contain the same ingredient – a natural chemical extracted from pine trees, called ‘pinene’. This material, when mixed with water, forms a natural polymer. That is to say, the molecules link together to form a plastic-like coating over the foliage of your plants. This coating slows down water loss, reducing and preventing winter-burn and desiccation injury in plants. Since this product is organic and natural, you do not need to worry that you are adding harmful or dangerous chemicals to your garden environment.

There are several ways to buy this product, but for anything other than a single small plant, the best approach is to buy a concentrate containing at least 25% pinene. This is diluted with water, and using a sprayer, applied to the plant until it drips off a little. At first your plants will look bluish-white, but once the spray dries it is completely transparent. You won’t have ugly burlap to look at, and no complicated staking and tying operations to do in the cold, either.

Tips on Using Anti-Desiccant Sprays

Like all products, these sprays need to be used correctly, to get the results you want. So here are some pointers to help you get the most from them:

  • Always follow the label instructions carefully. Choose the correct dilution rate for the time of year, and your purpose.
  • These sprays work best if applied when temperatures are around 40-50 degrees F. The plants should be dry when you apply it, and the spray needs time to dry afterward, so don’t spray when rain is expected in the next few hours.
  • Wait until December to spray your evergreens, or late November in the coldest areas. Plants must be completely dormant before applying, or else the spray will trap too much water in the leaves. This may then freeze and cause the leaf-cells to rupture, causing browning. When plants stop growing completely, the water in the leaves is reduced, so this problem will not happen once the plants are completely at rest.
  • Spray thoroughly, all over the plants, from top to bottom, including the underside of the leaves. Plants lose water from both the upper side and under side of the leaves, so you need to seal the whole plant.
  • If there are warm spells later in winter, take advantage of the temperatures being above freezing, and apply another coat. It does gradually wear off, and after a month or two it is not so effective. This is another reason for waiting as late as possible, and for re-applying once a month if you can.

Other Uses for Anti-Desiccant Sprays

Besides Arborvitae and other conifer-type evergreens, these sprays are very useful for boxwood, rhododendrons, holly and other broad-leaf evergreens growing in cold areas. They have even shown a benefit for climbing roses and hydrangeas, again when growing at the limits of their hardiness. One last tip – blue spruce is very hardy, and rarely suffers winter-burn. However don’t be tempted to spray them, as they have their own natural coating, which also gives them their blue color. Spraying will damage that, and make them unsightly.