March 4, 2010 at 8:57 a.m.

Prune your trees properly

Prune your trees properly
Prune your trees properly

As I was writing this article I received a call from someone who read my column on Colorado blue spruce not being be the best choice of tree to plant. He is in the nursery business and is concerned that those looking for trees to plant may be scared off by the title without reading the entire article. He is absolutely right that every species of tree has a downside, especially as they get older. The only tree that is not affected by something is the box elder tree. I have often said that when something attacks the box elder trees, the world is near the end.

In my article I compared the Colorado blue spruce that the Haralson brothers planted in our driveway to what modern day trees must put up with. Examples would be air pollution, salt and sulfur from roads, and debris preventing good air circulation, and overhead watering. By buying your spruce trees from a reputable nursery or garden center your Colorado blue spruce will have at least a so-so chance of survival.

I earlier wrote that late winter is the time to prune apple and most fruit trees. It is also a good time to prune most deciduous trees while they are dormant. Trees benefit from early pruning because there are few insects and disease pathogens at this time of year. Without leaves it's also easier to see problems such as branches that are damaged or rubbing together, double leaders, or narrow v-shaped crotches.

A few species such as maples and honey locust respond to early pruning by bleeding sap heavily from the wounds. This doesn't harm most trees but if you want to avoid excessive sap loss, wait until your trees are in full leaf. However, delaying is not an option for oak trees. Prune them from November through March, and never in April, May, or June. Open wounds leave them vulnerable to the oak wilt fungus carried by sap-feeding insects. If you must prune, use a latex-based paint to cover the wound, but only on oaks.

Delay pruning birch trees until July when they are in full leaf, and only prune when necessary. Fresh sap attracts female bronze birch borers looking for a tree on which to lay their eggs.

Use proper tools such as pruning shears, pruning saws, and loppers. Disinfect all cutting edges with a diluted bleach solution of one part bleach to nine parts water, or 70 percent denatured alcohol. After disinfecting, rinse the tools in water and wipe thoroughly with a dry rag to remove all remaining moisture and debris. Whether pruning or doing regular garden maintenance, it's always a good idea to disinfect your pruning tools often to reduce the spread of disease from one plant to another.

When you are about to cut a branch, find the collar. This is a doughnut of living callus tissue where the branch meets the tree trunk and it serves as the tree's natural barrier against pests and diseases. After you find this darkened line of rough bark, cut on the outside at a 45 to 60 degree angle. This will ensure that the tree will scar over and heal the wound. Recent research shows that one should not use wound paint as it interferes with the tree's natural defense against decay and disease.

When trees are young you can remove a great amount of wood with no ill effect. As they mature you should remove less and less. Never remove more than a third of a tree, and never cut off the entire top. Topping causes a flush of new growth that can severely weaken the tree, making it more susceptible to damage from pests and disease.

Information about our Spring Bonanza, plant order forms, and a schedule of our spring classes is going out to those on our mailing list. The Spring Gardening Bonanza will be held on Saturday, March 13, at Chisago Lake Lutheran Church in Center City. If you want more information on any of these events please call our Extension Office at 651-213-8904.




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