Winter watering evergreens in Bozeman means giving spruce, pine, fir, and arborvitae a slow, deep soak before the ground freezes and during dry, snow free spells after that. MSU Extension recommends watering at midday when temperatures are above 40 degrees and there is no snow cover, soaking the area under the canopy and out past the drip line rather than at the trunk. Newly planted trees and shrubs need it most.
Winter watering evergreens in Bozeman: one last deep drink before the ground freezes
Every spring the same thing shows up across the valley. A spruce that looked fine in October has a brown side by March. An arborvitae hedge has gone rusty. A young pine planted last year looks half dead.
Most of that damage was not done by cold. It was done by thirst, and it started months earlier.
Here is why evergreens dry out over a Bozeman winter, which ones are most at risk, and how to give them one last deep watering while the ground is still open.
Why evergreens dry out in a Bozeman winter
Deciduous trees drop their leaves and mostly shut down. Evergreens keep their needles, and those needles keep losing water all winter.
That loss speeds up on exactly the kind of days the valley gets plenty of. Dry air, wind, and bright sun reflecting off snow pull moisture out of the needles. When the ground is frozen, the roots cannot replace it. The tree slowly dries out from the top down and from the sunny side in, and the damage shows up as browning in late winter and spring. It is usually called winter burn or winter desiccation.
A tree that goes into winter well watered has a reserve to draw on. A tree that goes in dry does not.
Which trees need it most
Anything planted in the last few years. New trees and shrubs have small root systems and the least reserve. They are first on the list.
Spruce, fir, pine, and arborvitae. Needled and broadleaf evergreens lose the most water over winter. Junipers are tougher, but young ones still benefit.
Trees in hard places. South and west exposures, trees next to driveways and walks that radiate heat, trees in rock mulch, and trees in lawns where irrigation was shut down early all go into winter drier than they look.
When to water
MSU Extension's guidance is simple. Water at midday, when temperatures are above 40 degrees, and only when there is no snow cover. Midday gives the water time to soak in before it freezes overnight.
Once snow cover is established for the winter, there is no need to water. Snow insulates the roots and gives back moisture as it melts. A dusting that melts by afternoon does not count.
In most years the valley still gets a few of these windows in November, and occasional ones through the winter during long dry stretches without snow.
How to water
Slow and deep. The goal is to wet the soil about 12 inches down, where most of the roots are. A hose on a slow trickle or a soaker hose does this far better than a fast spray, which mostly runs off.
Water the drip line, not the trunk. Roots spread out under the whole canopy and beyond it. Move the hose around the outer edge of the branches rather than leaving it at the base of the tree.
Check it. A long screwdriver or soil probe should push in several inches without much force when the soil is wet enough.
Put the hose away after. Your irrigation system has been blown out, so this is a garden hose job. Disconnect it from the spigot when you are done and drain it, so neither the hose nor the spigot freezes overnight.
Mulch helps
A few inches of wood mulch over the root zone holds moisture in and keeps soil temperature steadier through freeze and thaw cycles. Keep it pulled back a few inches from the trunk, which also makes the base less inviting to voles.
What not to do
Do not turn the irrigation system back on. It has been winterized for a reason.
Do not water frozen ground. The water runs off or turns to ice instead of reaching the roots.
Do not fertilize now. Late season fertilizer encourages growth the plant cannot support going into winter.
If your evergreens browned last spring
Winter burn often looks worse than it is. Brown needles do not always mean dead branches, and the buds may still push new growth in spring. Before cutting anything out, wait to see what leafs out. If a tree is still declining after a full season, or if the damage keeps coming back on the same side every year, it is worth having someone look at the site, the soil, and the watering.
GVSS cares for properties year-round across the Gallatin Valley. If you would rather not think about any of this, that is what annual care is for.
Should I water my trees in winter in Montana?
Evergreens and recently planted trees benefit from it. MSU Extension recommends watering at midday when temperatures are above 40 degrees and there is no snow cover. Once snow cover is established, there is no need to water.
How much water does an evergreen need before winter?
Enough to wet the soil about 12 inches deep across the root zone. Water slowly with a hose on a trickle or a soaker hose, moving it around the drip line, so the water soaks in instead of running off.
Can I water trees when it is below freezing?
No. Frozen ground cannot absorb water, so it runs off or turns to ice. Wait for a day above 40 degrees and water around midday so it soaks in before night.
Why are my spruce trees turning brown in spring?
Often from winter desiccation, also called winter burn. Evergreens keep losing water through their needles all winter, and when the ground is frozen the roots cannot replace it. Dry fall conditions, wind, and sun make it worse, especially on south and west sides.
Do I need to water if it already snowed?
Not once snow cover has settled in for the season, because it insulates the roots and adds moisture as it melts. A light snow that melts the same day does not change much, so if the ground is bare and dry again, watering on a warm day still helps.