Watering outdoor plants probably isn’t on your traditional December to-do list, but perhaps it should be – especially this December. For more on the matter, we turned to Woody Wood from our Plant Care team and Scott Evans of Nebraska Extension in Douglas and Sarpy Counties. Scott says winter-watering has been a hot topic for the Extension team this month because the last time our area received any meaningful precipitation was October 14th. October 14th – that’s over two months ago. But, do the plants in our landscapes really need water now? After all, it’s cold outside, and most plants are dormant for the winter, right? It may come as a surprise that although they look pretty inactive right now, our landscape plants aren’t completely asleep and need at least some moisture in the cold months too. Before the ground freezes solid, we should take steps to make sure our outdoor plants are getting the water they need to stay hydrated and come back healthy and strong again in the spring.
The Problems Caused by a Winter Drought
Although sometimes it’s hard to see it at first, long, dry periods in the fall and winter can lead to noticeable damage to some of our woody trees, shrubs, and herbaceous perennials. Scott says that without the insulating properties of water, dry soil allows frost to penetrate deeper into the soil. Dry soil is also more prone to cracking as it freezes and thaws. Frost and cracks expose tender roots to frigid temperatures and drying winds, particularly in exposed areas. Low humidity and wind also increase the rate at which landscape plants lose moisture through their stems and foliage. But, dormant plants can’t show us they need water – they look the same, thirsty or not. And when early spring comes, the affected plants may use stored energy to put out an encouraging show of new growth and flowers. So, as gardeners, we tend to think dry winter weather isn’t a big deal and watering isn’t important once it’s cold. But when summer’s warmth arrives, the damage caused by a dry winter may reveal itself in losses to parts of – or even entire – plants. Put it all together and, as Woody points out, a winter drought can be even more damaging to plants than a summer one.
What to Water
Any of our landscape plantings would probably benefit from a drink now and then through the winter, but there are some that are particularly sensitive to dry soil and drying winds during the cold weather. According to Colorado State University Extension, we should pay attention to trees and shrubs with naturally shallow root systems such as birch, linden, red and hybrid maples, willow, and dogwood. To this list, Woody added any type of newly-planted trees, shrubs, roses, and herbaceous perennials, especially those planted since August. New plantings haven’t had time to establish deep root systems that can find moisture further into the soil. Woody also said that conifers like pine, spruce, and fir, as well as broadleaf evergreens like boxwood and rhododendron – whatever their age – are prone to over-drying in the winter. The foliage of these plants stays all year and continues to lose moisture in cold weather – moisture that can’t be replaced through the roots if the soil is dry or frozen. And don’t forget your holiday planters made with fresh-cut greens. The evergreen boughs will stay green and fresh much longer if the soil in the container is kept well-watered until it freezes. As for lawns, they’re not usually a priority for winter-watering. Our grass lawns have deep root systems that help them tolerate dry winters, and with our in-ground sprinkler systems shut off, it’s not worth the hassle of watering the entire lawn by hand.
How to Water
Fortunately, there are ways to mitigate the effects of fall and winter drought on our plants. The most important way is to water our susceptible plants when natural precipitation is lacking like it has been recently. How much water you’ll need and how often you’ll water will depend on the type and size of plant. For trees and large shrubs, Scott suggests giving ten gallons of water for every inch of trunk diameter and applying it all around the tree, staying underneath the canopy. Smaller shrubs can receive half of that. For perennials, apply one gallon of water for every foot of plant height.
When you water, choose a nicer day that’s above forty degrees so the water has a chance to soak deeply into the soil before it freezes. We don’t want to use our sprinkler systems now though – when temperatures drop below freezing, the pipes could burst and cause flooding in the house. Woody suggests that the best method for watering now is with a hose, applying a slow five- to ten-minute soak at multiple locations around each plant. She also stressed the importance of draining and disconnecting the hose after each use to avoid damage to our plumbing.
And how often do we need to water? A lot depends on how much natural precipitation we’ve received and how windy it’s been. A great way to check soil moisture is by sticking a long screwdriver into the soil around your plants. If the screwdriver is difficult to push in and comes out dry, it’s time to water. In weather like we’ve had lately, Scott estimates that watering every two to three weeks may be necessary. The screwdriver is also good for checking to see if the surface of the ground is frozen. If it is, don’t water because any water you apply will just run off without soaking in. If we get a warm spell later in the winter, and the ground warms up again, you can resume watering if we still haven’t had much snow.
Other Winter Measures
Once our plants are hydrated, we can help them conserve that valuable soil moisture by applying a layer of mulch. Mulch also acts like a blanket to help protect the soil from extreme temperature fluctuations that can cause heaving and cracking. To reduce the amount of moisture lost from evergreen foliage, we can use a product called Wilt-Pruf. It’s made from pine oils, and when sprayed on conifers and broadleaf evergreens, it creates an invisible protective coating that helps the foliage maintain moisture. To work properly, Wilt-Pruf should be applied when temperatures are above forty degrees, so it’s best to choose a nice day to spray it.
Even though it’s chilly outside, your landscape plants still need a drink now and then to stay healthy all winter and make a beautiful comeback in the spring. If you have any questions about winter-watering, mulching, or applying Wilt-Pruf, come visit with one of our team members – we’re happy to help.
