Your trees need water in the winter too, though not as much as during the warmer months. In cold months they are not transpiring water through their leaves, but on those warm winter days they are still respiring in their roots and stems. All cells need to burn energy to survive, including the cells that are photosynthesizing! Root cells not only respire a good deal to maintain homeostasis but are actively growing during the warmer winter months. For weeks after the leaves are shed from deciduous trees, the roots continue to expand and explore their surroundings.
Why should you water?
While water is not directly involved in cellular respiration, it is a major contributor to cellular functions. Nutrient uptake and transport are aided by water. Water is the solvent in which our organelles float around, and it plays a key role in osmosis. The swelling of plant cells (called turgor pressure) is the way in which plant cells elongate. Without the presence of abundant water, plant cells will not elongate as much and the growth increments of trees will be diminished.
Another big reason to water in the winter is to preserve the long vertical water columns in the stems of trees. The xylem vessels that passively transport water up the trunk of trees during the summer are holding water in the winter. A break in the water column is detrimental to the tree as the tree cannot patch large breaks back together. Colorado’s long dry winters put stress on these water columns and often break them. This can sometimes be heard on cold nights.
A consequence of these broken water columns is what the industry calls “sunscald”. Sunscald in a large vertical crack in the bark of the tree. It can have various causes, but researchers are finding that winter desiccation could be a major contributor.
When should I water?
Cellular metabolism isn’t doing much when it's so cold you can’t even wiggle your fingers. Things just slow down! So you don’t really need to be watering if it's colder than 40 degrees F. Also, if there is snow and ice on the ground beneath your tree you probably don’t need to water.
How much should I water?
Trees are not transpiring water in the winter, therefore they do not have many water needs. For southwest Colorado, a monthly watering during the winter should be adequate. If there is a long dry spell maybe twice a month. What we don’t want to do is to drown the roots. Because roots are respiring, they need oxygen too. A root that is submerged in water does not have access to oxygen and will start to resort to other modes of survival that ultimately will cause tissue damage and death. Therefore, over-watering is a bad thing! Make sure you know your soil types and watering needs before continuing. What we want is soil moisture at “field capacity”. This is the amount of water left in the soil after gravity and diffusion has wicked the excess water away.
What trees need water?
Generally, trees that are well established or natural to the area (meaning you didn’t plant them) do not need supplemental water in the winter. Trees that you planted (especially ones you planted in the past few years) and trees not native to the region need supplemental water. These “landscape” trees have an adjusted root structure that allowed them to be moved to your lawn and recover quickly from their transplant shock. For a long time, they won’t be able to access deep water sources, and depending on the site they may never do so. Trees grown in urban environments often have other stresses such as salts, pollution, and limited rooting space that prevents them from accessing not only water, but also resources. These trees need a little extra care and we can talk about that in another blog.
Is this topic applicable to other parts of the country? Maybe where my family lives in Arkansas or Florida?
Yes and no. Each region is unique in weather conditions, soil types, and vegetation needs. So consider talking to a certified arborist to decide if you need to be winter watering.
And does Florida even have a winter?
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