January 29, 2004 at 1:07 p.m.
If red-brown foliage appears on Colorado blue spruce and red pines, the injury is usually due to freezing following a spell of warm weather. Often, winter injury begins where the snow line ends. This results in the upper half of the tree having reddish-brown needles, while the lower half which is protected by the snow remains green. If we do get ample snow in the last part of the winter it could prevent winter injury of young conifers by providing shelter from drying winds and sun glare. The browning of evergreens such as arborvitae and yew may not show up until May and June.
Regardless of the type of evergreen you have, wait to prune affected branches until bud break occurs. Although many needles may be lost, the buds are usually protected and will leaf out come spring. By waiting for bud break, you can better determine the damaged area. Prune out any affected portion, removing only the dead branches.
If the winter gets bitter cold with little snow cover, there could be root and trunk injury on hardwood trees. This type of injury will not be obvious until warmer weather is here. The symptoms could include early leafing out or no leafing at all. This is followed by shoot death (the shoots wilt and die) when the warm weather comes.
Another type of winter injury that affects hardwoods is sun scald. Sun scald and bark cracks occur primarily on the south and southwest sides of smooth barked trees and shrubs. Maple and other thin barked trees seem to be particularly vulnerable, followed by apple and other fruit trees, linden and mountain ash. This injury is caused by the sun warming the south side of the tree while the shaded portion remains frozen. When the sun sets it will freeze again. This can result in vertical cracks in the bark which can lead to death of the cambium layer, resulting in the death of the tree. The crack can also provide an entry for insects, disease and decay.
There should always be a reason for pruning and this is the time of year for pruning some kinds of trees. Oak trees should be pruned during December, January and February to guard against oak wilt infection.
Some recommend that birch trees should not be pruned until late summer to avoid attracting the bronze birch borer.
One may not want to prune maples, ironwood, honey locust and black walnut in February or March because they tend to bleed sap. Although this won’t hurt the tree, if you wait until the tree has leafed out the bleeding will be minimized.
Pruning spring blooming shrubs in winter will reduce its flowering because you will be removing some of the flower buds. To avoid this, all spring flowering shrubs such as forsythia, lilac and azaleas should be pruned right after they have finished blooming.
Don’t be afraid to remove overgrown shrubs that no longer contribute to the landscape or are not serving their purpose. A good example of this is redtwig and yellow dogwoods which can be pruned in March. Their stems lose their color as they grow old. Pruning out old, thick stems each year will encourage new growth.
Our office is always receiving questions about when and how to prune. Ken Schroepfer, Isanti County Master Gardener will be teaching a class at our upcoming gardening bonanza on when, where, how and why to prune your trees and shrubs, including proper techniques, thinning, cutting back, rejuvenation and what tools to use.
Reminder: The new number for your gardening questions is 651-237-3080. The new email address is: [email protected]
Brochures are available for Bonanza 2004 “Garden Fever” which will be held at Maranatha Church in Forest Lake on March 6. Pre-registration is strongly encouraged. Call or email to receive a brochure or are interested in being a vendor. Forms are also now available to preorder bare root strawberry, raspberry, blueberry and grape plants. Many of these are cultivars developed at the University of Minnesota and used by commercial growers, but hard to find for home use.