As the gardening season winds down and fall colors set in, a sense of relief may set in that the time for constant yard work is ending for the season. In the past, winter is time for people to rest and recharge between busy gardening seasons, but changing winter climate may disrupt this rest period. Winters are supposed to recharge the land. Snowpack insulates the root systems of trees and shrubs, winter precipitation builds soil moisture, and frozen ground helps preserve moisture until spring. But lately, southern Wisconsin has been seeing winters that are, in many places, significantly drier than what locals expect.
Last year, Southern Wisconsin entered a drought period at the beginning of October that lasted through the Winter. We saw very little autumn rain, and almost no snow all winter. This had some wide ranging adverse effects on our trees and shrubs. Snow is more than scenic. It insulates roots, reduces moisture loss, and keeps winter injury in check. Periods with minimal snow meant that tree roots weren’t protected from cold snaps, leading to root injury that later caused branch dieback. Because there wasn’t enough snow, and because temperatures were warmer at times (which speeds up evaporation even of shallow snow), soil moisture was lower than usual throughout the Winter and early Spring. This led to additional root damage and contributed to large numbers of young trees and shrubs dying altogether this past Spring. It also led to large outbreaks of vascular canker diseases such as Sphaeropsis canker, which attacks vulnerable trees and shrubs. Conifers like pines, spruces, and arborvitae keep their needles all year and are especially vulnerable to dry winters. In winter droughts, they continue losing moisture through needles but can’t replace it from frozen or dry soils. The result is winter burn causing brown, scorched foliage that appears in spring. Young trees, trees with shallow roots, and species planted in urban settings with limited root space are especially vulnerable to winter drought stress.
Even though we had a rainy spring, many trees have a harder time recovering from these conditions. Trees that start out from a moisture deficit are more vulnerable later to heat, humidity, and the effects of too much or too little rain. This year, we are asking our clients to watch out for similar conditions forming again, and to get out and water their trees. Even though a tree has lost its leaves for the year, it still needs some water. Trees still uptake water and nutrients from their root systems into the Fall and through the Winter, although at slower rates. So, if we see another drought-y Fall, and another winter of no snow, think of your trees!
Since winter watering recommendations are a new thing for our area, it’s hard to know exactly how much and how often trees may need water in the winter. Consider these general guidelines. Whenever there is no snow, and the ground is not frozen, get out and check the soil moisture. The ground should be consistently moist several inches down. If the soil around your tree’s root zone seems dry, give it some water. Even though many people’s hose spigots are turned off for the year, filling up buckets inside and pouring them around your tree’s root zones can help reduce the effects of another stressful winter. If you are unsure if your trees need watering this winter, contact our ISA Certified Arborists, and we can help guide you on your tree’s needs.