You might think your trees and shrubs don’t need to be watered in winter. After all, the plants are dormant, it’s cold outside, and everything is blanketed in snow. But chances are they do need water. Winter water stress and dehydration in trees are very common in Connecticut, especially during periods of dry, windy, and freezing winter weather, as well as along the coast.
Lack of water in winter causes root damage and desiccated foliage; in severe cases, it can kill the plant. Thankfully, it’s fairly simple to provide the supplemental irrigation needed to protect your valuable trees and shrubs this winter. Come spring, your trees will be healthy, hydrated, and ready to emerge from their dormancy.
In this article, we explain:
- Why dormant trees still need water in winter
- How to tell whether a dormant tree is dehydrated (external signs of water stress)
- How trees lose water in winter and what it does to them
- The effects of temperature, wind, and salt on winter dehydration (living by Long Island Sound gives you beautiful views but it can wreak havoc on plants)
- How to water trees and landscape plants in winter
- What to use for winter watering (because you can’t use your irrigation system!)
- How much water your trees need in winter
- Ways to measure whether or not your plants have enough water
- Other ways to help prevent winter dehydration in trees and shrubs
Dormant Trees Still Need Water!
A tree with bare branches is one of the most recognizable symbols of winter. But those ghostly branches don’t mean the tree isn’t still active and alive, and using (and needing!) water. While a dormant tree may not be producing visible new leaves or flowers, under the bark and below the soil surface it’s business as usual. And that requires water.
Tree Roots are Hard at Work in Winter
A tree is a living thing and its roots are like its beating heart. Tree roots never go dormant; even in winter, they’re hard at work. Roots pull moisture up from the soil into the tree to keep the tree’s internal system hydrated and its “water pressure” balanced.
Trees use roots to regulate their internal water levels and the hydraulics of their vascular system. Roots pull up water from the soil. From there, the tree’s internal pressure keeps it moving through the tree all the way up to the terminal leader, or growth tip, at the very top of the tree’s crown.
When it rains, or when you irrigate your tree, water soaks down into the soil where tiny, filament-like feeder roots are growing. These roots then take up the water and use it to hydrate the tree.
Tree and shrub roots can be found anywhere from twelve inches below the soil surface to four feet below it. To reach those roots, winter rainstorms and melting snowfall have to provide enough water to soak the soil down to root depth. And since this doesn’t always happen, you’ll need to make up the difference by watering your trees and shrubs by hand.
How to Identify Winter Dehydration in Trees and Shrubs
If you’ve ever seen a drooping stem or a wilting leaf in summer when it’s hot and dry, you’re seeing insufficient water volume and water pressure in a plant’s vascular system, AKA dehydration. In winter, you won’t see this external sign of water stress in your deciduous trees, but you can in evergreen tree species and evergreen shrubs. Here are the signs of winter dehydration to look out for:
- Evergreens such as conifers, boxwood, hollies, and kalmia will exhibit water stress in winter through brown, dead leaves, leaf tips, and leaf margins.
- Twigs and terminal branches can also die back from winter water stress, making the whole plant look scorched or diseased.
- Desiccated winter foliage can also be caused by – or exacerbated by – road salt and salt spray.
Winter dryness, combined with extended periods of low or freezing temperatures and strong winds, can be severely damaging or fatal to even the hardiest tree and shrub species.
Trees Lose Water Through Leaves, Even in Winter
Even during dormancy, evergreen trees are still photosynthesizing and transpiring. In other words, they’re still releasing oxygen and precious water through their leaves, although at a much slower rate than during the growing season.
To take in carbon dioxide and make food energy for the tree, a leaf must have an absorbent lens of water on its surface. Winter wind and cold, dry air increase the rate at which this film of water evaporates. To compensate, leaves must draw on their internal water reserves, leaving less water inside the leaves.
If a tree is already water-stressed in winter (or at any time of the year), dry and windy conditions will increase the rate and severity of the tree’s dehydration and its foliage damage. In severe cases, the leaves dry out, turning brown and crispy before falling off.
How Winter Watering Helps Plants Survive
The best way to mitigate this damage and help your trees survive is to provide supplemental winter irrigation. Winter watering will:
- increase available soil water
- replenish a tree’s internal water stores
- allow transpiration and photosynthesis in leaves
- prevent leaves from drying out, dying, and turning brown
- wash away accumulated winter salt in soil
Connecticut winters usually bring rainstorms. But if those storms are infrequent or light, winter watering will make up the difference and keep soil well-saturated with water for roots to absorb.
Location Affects Trees’ Winter Water Needs
Environmental conditions in winter play a big part in the health and vigor of your trees. When there’s sufficient rain and soil moisture levels are replenished, trees are healthier and better equipped to withstand environmental stresses such as freezing temperatures, wind, and salt spray. When there isn’t enough water, it’s harder for trees to endure these winter conditions without damage.
Freezing Temperatures and Dry Soil
Extended periods of cold weather may bring snow, but snow doesn’t have much water volume.
- A rough estimate of water in snow is that 10 inches of snow will produce 1 inch of water. This can be higher if heavy, wet snow falls instead of dry, powdery snow, but it gives you an idea of just how much snow is needed to provide sufficient irrigation water.
- Any water held in snow won’t be available to tree roots until freezing temperatures rise enough to melt the snow.
- Freezing temperatures also freeze soil, making it hard or impossible for water to penetrate the soil’s surface and reach roots below.
- Dry winter soil won’t insulate tree roots the way moist, hydrated soil will. Plus, dry soil doesn’t support the beneficial microbes and mineral nutrient bonding that are vital to long-term soil fertility and tree health.
Salt and Wind
Salty or saline water, as well as salt spray, are damaging to trees and shrubs and can kill foliage and roots. We’re most likely to see salt-damaged plants along roadways that are salted in winter, snowbanks from areas that use snow and ice-melt products, and near Long Island Sound (salt spray can be blown as much as ¼ mile inland during winter storms!).
Here are the important facts about winter salt damage:
- Salt burns leaf tissue, making it brown and dry.
- Winter winds can blow snow off soil surfaces, allowing salt spray to saturate the soil and freezing temperatures to reach delicate feeder roots.
- Winter winds and salt spray both dry out leaves and deposit salt. This damages the leaf’s surface and reduces its ability to photosynthesize and replenish food energy reserves.
- Salty water in soil is taken up by roots and sent to the leaves. As the saline water is released through pores on the leaf surface, its corrosive properties kill the leaf tissue.
The best remedy for winter salt in soil is to flush the soil with water. This dilutes the salt concentration and washes it down and out into the soil and away from sensitive feeder roots. During a dry winter when there isn’t enough rain, you’ll have to do this with supplemental irrigation.
How to Water Your Trees and Shrubs During Winter
Just like in summer, your supplemental winter watering should be “low and slow,” to allow water to soak into the soil and reach root systems. But winter means cold or freezing temperatures, which means your soil is going to be less friable and less immediately absorbent.
You’ll need to wait for a clear day when temperatures rise and remain warm enough for soil to thaw and allow water to soak in. Don’t water unless temperatures rise to at least 40 degrees and there’s no snow cover on the soil you’re irrigating.
Since tree roots can be several feet below the soil surface, it takes time to thoroughly irrigate them. And because winter daylight hours are short, it’s best to start watering as early in the day as temperatures allow (late morning or noon). This ensures there’s enough time for irrigation water to move down into the soil to reach roots before freezing temperatures return in the late afternoon.
Weather forecasts are your friend! Use them to plan out your winter watering schedule to take advantage of each warm, clear day.
What to Use to Irrigate Your Trees and Shrubs in Winter
If you have an irrigation system, it should already have been drained and shut off for the winter. Don’t turn it back on and risk pipe freezing and rupturing! There are other ways to water plants in winter.
Depending on the size of your garden and the number of trees and shrubs that need winter watering, you can choose from these options:
These are good for small plants that don’t need a lot of water. You can fill up your watering can (or a bucket, we’re not fancy) from your kitchen faucet or an insulated and protected hose bibb. Slowly and thoroughly water around the base of the plants, out to the extent of the rootball.
Chances are you’ll need to make multiple trips, as watering cans are designed to hold manageable volumes of water that a person can carry. Remember that a gallon of water weighs over eight pounds!
And remember, don’t dump water from watering cans or buckets all at once.
- Too much water applied all at once will run off instead of soaking into the soil.
- The force of water will wash away mulch and soil that protect your plant’s roots, increasing the chance that they’ll be killed by freezing temperatures.
Perforated Jugs or Buckets
If you have plastic milk jugs or buckets (the 5-gallon buckets from big box stores work well), punch a few small holes in their base. Place each jug or bucket beside a plant, fill it with water, and let the water slowly drain through the holes into the soil. Refill them as often as needed to thoroughly water the plant.
A hose is your best bet if you have more than a few plants to water, large shrubs and trees, or if your plants are some distance from your water source. The novelty of lugging water wears off fast!
After attaching your hose to a hose bibb, turn the water on so that a slow trickle comes out. Place the end of the hose near the dripline of the tree. You may need to move it a few times around the perimeter of a large dripline, so set a timer to remind yourself if you’re doing other things. For large trees and shrubs, it’s important to evenly water their whole root system.
When you’re done watering your plants, remember to drain your hose of any remaining water, coil it up, and store it where temperatures don’t drop to freezing. That way your hose will stay flexible, resist cracking, and be ready for the next warm, clear winter day.
How Much to Water Trees in Winter
A truly accurate calculation of how much water you need to irrigate your trees requires some complex calculations that involve:
- soil infiltration rates
- irrigation pipe size
- number of irrigation emitters and their flow rate
- weather sensors, and more.
Instead, we’ll use a rule of thumb (a best guess based on available information) – it’s much easier!
For each inch of trunk diameter, you’ll want to apply about ten (10) gallons of water. Measure the diameter of your tree’s trunk 6 inches (roughly a hand’s breadth) above the soil surface. If you measure the circumference of your trunk with a tape measure, divide the number by 3 (or pi) to get a rough diameter size.
So, if the trunk circumference is 18 inches, that means the diameter of your tree is roughly six inches and you’ll need 60 gallons of water to irrigate it.
PRO TIP: If you’re using a garden hose to water your tree, you’ll also want to know how long to run the water to reach 60 gallons of flow. You can use a flow meter attached to your hose bibb, or you can improvise! Find a gallon container like a milk jug or bucket, turn your water on to a trickle, and time how long it takes for the hose to fill the container. Then multiply that time by the number of gallons you need for irrigation. If it takes one minute to fill a one-gallon jug, it will take 60 minutes, or one hour, to let 60 gallons of water flow from the hose to your tree.
How to Know When You’ve Watered Enough
In summer, it’s easy to see when a plant or tree is well watered and not dehydrated:
- It’s a normal size and isn’t stunted or twisted
- The leaves and stems are green and turgid, not drooping or undersized
- There are no dead, brown, or scorched foliage
- It hasn’t dropped its flowers or fruit prematurely
In winter, you won’t have these visual clues to tell you if your tree is water-stressed. Instead, try the following methods to see if there’s enough water in your tree’s root zone:
- Use the rough trunk diameter calculation above to get the volume of water your tree needs
- If temperatures are high enough and your soil has thawed, dig down in the soil 12 inches to check its moisture. Remember to dig your exploratory hole away from the root systems of your plants so that you don’t damage them.
- Invest in a good-quality soil moisture meter and, when the soil is warm and thawed, stick it at least 12 inches into the soil for a moisture reading.
If your investigations show that your soil is dry, irrigate. During a dry, cold, or windy winter period, you should plan on irrigating every two to three weeks, depending on weather events and the size of your trees and shrubs.
Just as in summer, bigger plants = more roots = more watering, more often in winter.
Other Ways to Prevent Winter Dehydration in Trees and Shrubs
Irrigate During the Growing Season
Protecting your trees from winter dryness and drought starts long before winter begins. What you do during the growing season will have a huge effect on a tree’s ability to survive through winter.
- Irrigate regularly during hot weather. This will keep your trees healthier as dormancy and cold weather approach because water and energy stores in the trees will be at their optimum levels. Both plant tissue and soil are better able to withstand severe winter weather if they are already hydrated and haven’t been stressed by summer drought and heat
- Be ready to continue irrigating your trees in fall, even after leaves fall. Just because your deciduous trees are bare doesn’t mean they’re not alive inside
“Insulate” With Compost
Add compost to the soil in spring, summer, or fall. This not only increases nutrient levels, but also improves soil’s moisture-holding ability. The more water molecules that bond to soil particles, the more water available to roots year round.
Adding a thick layer of organic mulch to your soil surface will provide several benefits at once:
- Organic mulch slowly breaks down and enriches soil.
- A minimum three-inch layer of mulch slows the evaporation of water from soil in winter, and year-round.
- Mulch insulates, regulating both high and low soil temperatures and protecting roots from water stress.
When you add mulch, just make sure it’s in a layer thick enough to provide its benefits and keep it away from the base of your trees’ trunk. No mulch volcanoes and no water-holding material like wood chips touching the trunk flare and creating a place for fungus and bacteria to grow.
Keep Track of the Weather
As climate change makes Connecticut winter weather patterns less predictable, it’s more important than ever to use all the methods available to keep your trees and shrubs healthy, watered, and able to withstand periods of drought.
Historic and current weather information, as well as drought measurements for all areas of Connecticut, can be found through the North American Drought Monitor.
If a dry or warm winter is predicted, plan ahead to protect your trees from winter water stress and dehydration by using the measures we discussed above.
Improve Your Garden’s Overall Health
The healthier your garden is overall, the better prepared it will be to survive periods of winter drought. If you’ve got valuable trees and shrubs, it’s worthwhile investing in the plant health care practices that will keep them vigorous and healthy throughout the year.
Give Us a Call
If you have any questions or concerns about watering trees in winter or the health and appearance of your trees and shrubs in winter, just give us a call. We’re here to help diagnose any issues affecting your landscape plants and suggest options to maintain or improve their health. You may find that all it takes is an annual schedule for fertilization, irrigation, and soil amendment to help your trees and shrubs sail through winter’s worst and be ready for spring.
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