The combination of warm temperatures and lack of precipitation across the state means homeowners may need to water their trees and shrubs, says John Ball, SDSU Professor of Plant Science and Extension Forestry Specialist.
 
"Evergreens are particularly at risk for dehydration because they might be actively losing water from transpiration, as well as evaporation from the soil surface," said Ball. "I've received many calls from homeowners wondering if they should water, particularly trees and shrubs that were planted last year and have not had time to establish a large root system. The answer is yes. Water if your soil is not frozen, and if it is beginning to dry out."
 
Before watering, Ball suggests using a trowel or spade and dig down at least 6 inches into the soil profile to check if the soil is frozen.
 
Rhoda Burrows, Extension Horticulture Specialist adds that even fruiting plants such as raspberries or grapes may need watering, especially if they were just planted last year.
 
Ball adds that if the soil is frozen it may not be a good idea to water.
 
"Water movement up stems during winter days with air temperatures slightly above freezing does not occur on most woody species, or is extremely slow.  Also, soil temperatures influence root permeability and water uptake at 33 degrees may be only one-fifth of that at soil temperatures near 60 degrees to 70 degrees.  If the soil is still frozen at 4 inches or so you might find that the water does not infiltrate into the soil and instead forms a layer of ice over the turf.  It is best to check the soil first, to be sure the water will be absorbed before adding any," Ball said
 
However, if the soil is not frozen, he says winter watering may be a good solution for shrubs and small trees.
 
"If the trees or shrubs are located along the south side of homes where the daytime air temperatures can reach at least 50 degrees and even higher," Ball said.
 
He adds that the best way to water woody plants during the winter is to only water when the soils are not frozen and the air temperatures are above 40 degrees.
 
"Restrict watering to mid-day so that the water will have an opportunity to soak into the soil before night. However if the trunk is still frozen, even this water will not be absorbed," Ball said.

 
Warm temperatures may induce winter kill

Ball says he expects to see more winter kill in trees and shurbs this year due to the warm winter temperatures.
 
"I expect to see more winter-kill this spring as well as, calls from people noticing their flowering trees and shrubs are not flowering as much as normal or not at all," Ball said.
 
He explains that the process for woody plants acclimating to winter begins in late summer as the days become shorter and accelerates as the plants are exposed to autumn frosts.  Once trees and shrubs have reached their fully hardiness they are set to endure our cold winters.
 
"Usually plants reach their full winter hardiness by mid-January allowing many woody plants to survive temperatures as low as -40 degrees without injury.  Much of "winter" injury of woody plants in South Dakota occurs when plants are coming out of dormancy in the spring and there is an unusual dip of cold weather," Ball said. "This year we may see even more "winter" injury as the unseasonably warm weather is beginning to coax some plants out of their dormancy prematurely. We are already seeing flower buds for many of our spring flowering shrubs expanding as well as the leaf buds to some tree species. These plants are beginning to lose their tolerance to extremely cold temperatures and if, or I should say when, we experience subzero weather, the tender buds and shoots may be killed. "

Ball says the extent of injury a particular plant might receive may not be known until later this winter after - we have the inevitable cold snap.
 
To understand how much injury a plant has received, Ball says in early March homeowners can pull away the bark from one year old twig.
 
"If the wood is light colored, the tissue did not experience cold injury and the plant should be fine, but if the wood is brown it was injured by the cold," Ball said.

Wait to prune

Despite the warm weather making yard work easier at this time, Ball suggests delaying any pruning until late March.
 
"It might be best to delay pruning, particularly ornamental flowering trees and fruit trees until late March, just before bud break.  At that time any of the shoots that were killed by the cold will be easier to see since their buds will be shrunken and dry, rather than large and soft," Ball said.