Master Gardener: Arborvitae generally tolerant of cold weather
BY BRIAN JERVIS Ask a Master Gardener
Saturday, December 29, 2012
12/29/12 at 5:24 AM
Q: Some of my arborvitaes died last summer. The ones that survived now are losing leaves, and I am afraid a hard winter may kill them. What should I do? Sue B., TulsaA:
The Eastern arborvitae, or Thuja occidentalis, is a beautiful, graceful evergreen landscape plant. It is widely used for screens and hedges, but it has its limits of heat tolerance. The cold hardiness zone for most arborvitae cultivars is from 2 to 7. Tulsa is in zone 7, the warm end of its temperature tolerance. In the Tulsa area numerous arborvitae died over the past two summers due to the extreme heat and drought. Many of these died in spite of receiving regular watering.
Arborvitae do have some insect and disease issues, but the cause of the leaf drop on inner limbs in the fall is normal. They may shed old leaves at the end of the season like deciduous trees and pines. They may also develop insignificant "winter browning" when there is a dry wind and there are sudden drops of temperature. Their cold tolerance is generally good.
Suggested care of arborvitae in winter is similar to recommendations for most plants. First of all, plants should be selected for our cold-hardiness zones. If so, they usually do well in winter with no special care. Those plants marginally hardy in our area do best with some form of protection from dry, cold winter winds.
The biggest risk to any plant, especially an evergreen such as arborvitae, is dehydration - either due to inadequate watering or an underdeveloped root system, often found in young plants. It's important to remember that watering, whether it is precipitation or irrigation, is just as important in the winter months as it is in summer. Don't forget about foundation plants under roof eaves that may receive no rain. Likewise, outside plants in pots will need extra water; most potting soils cannot hold on to water.
Young trees with long, bare trunks, such as maples, will benefit from paper trunk wrappings available at garden centers. This prevents rapid freezing and thawing of the thin bark, a cause of bark splits. Apply them now and remove in spring. Remember that mulch is your plant's best friend, both winter and summer. Mulch has a long list of benefits.
Pruning may be done now, but some feel it is best to wait until late winter for general pruning of shrubs and young trees. Pruning removes energy stores that the plant may need for winter. Prune anytime if you have dead or diseased limbs.
If you have a garden-related question for the Master Gardeners to answer in a column, call 918-746-3701.
There are several options for your Christmas trees. They may be placed close to bird feeders for winter shelter, weighted and dropped in a fishing hole at a lake or pond or shredded and used for compost or mulch.
Another option is to take the used trees with all ornaments removed to Tulsa's Green Waste site on 56th Street North, just west of Highway 169. They are open to recycle all green waste at no cost with proof of residency in Tulsa.
Trees can also be placed with your trash for pickup by the city's service. However, trees will have to be cut and tied into bundles no larger than 4 by 2 feet, according to current regulations.
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