By Mike Allen
Written for Winnipeg Free Press ‘Tree Care’ Column November 7, 2004
I have chosen a few questions that I have received from readers in recent months that I thought I would share with you along with my responses. Questions regarding evergreen trees and shrubs make up three-quarters of the inquiries I receive.
Q. My large blue spruce tree has lost thousands of needles and several branches are dead. Will the tree ever grow back new branches? Jean W., Winnipeg
A. Spruce trees can sometimes surprise us with their ability to grow a second set of branches replacing those that died. Unfortunately not every spruce can do this. Here are some ideas you might want to try to encourage branch regrowth in your tree.
The three most significant causes of dead branches in urban and shelterbelt spruce trees are (1) white blister (Cytospora) fungus canker disease, (2) spruce spider mites, and (3) competition from itself through shading, other trees through shading and physical abrasion, and buildings. When increased light hits even diseased branches and trunks of spruce, it often stimulates growth of new shoots from buds located just under the bark. Aerating and fertilizing the tree will keep the disease in check; and power water washing infested branches will help control spider mites and other pests. Under these improved growth conditions, those new shoots will develop into longer branches. I have seen many 60 foot white spruce trees in Charleswood grow prolific new branches up to 12 feet long in the once branchless lower half of their trunks creating a columnar spruce effect – a very impressive sight.
Q. I need to prune my globe cedars as they are blocking part of my front window. Can I do this safely without injuring them? When is the best time to prune them? Bob H. East St. Paul
A. Like most coniferous evergreens such as spruce, pine, juniper and fir, it is a rule of thumb that no more than a quarter of the existing green growth, including twigs and branches, be removed in any one year. The best time to train and prune the cedars is before they get to be a problem for your location. This would have been when the plants reached about half-way to two-thirds of the way to the height of the window sill. Pruning the cedars at one level such as the bottom of the window sill will eventually cause the depletion of green leaves and create a bare looking plants that will be unattractive to look at. The cedars will also be significantly weakened in health. Removal of the cedars and starting again are now the best strategies. Cedars rarely produce new shoots on leafless twigs and branches as spruce trees sometimes do. June is the best month to trim all evergreens.
Q. Our silver maple tree is over 50 feet high and dying. Its leaves are light yellow with brown spots on them. Many leaves have curled, turned brown and have fallen off. I am concerned that the tree is diseased and that it will fall over. Can I get it topped? Doug C., St. Vital
A. I recommend treating the leaf problem first. The maple has chlorosis (yellow leaves with prominent green veins) which is sign of iron deficiency in the soil. With treatment the tree should not die. Annual spring fertilizing with a high nitrogen fertilizer and an iron chelate supplement will restore the green colour of the tree’s leaves over 2 to 3 years. Silver maple trees do not topple over unless their roots have been damaged through significant ground disturbance such as construction. Ask a reputable arborist such as one certified through the International Society of Arboriculture (ISA) to reduce the crown of the maple using proper arboricultural techniques. All commercial arborists in Manitoba must have a valid Manitoba Arborist License to operate their business. Most of those arborists are not ISA certified.
Topping mature trees of any kind is always a destructive practice. Removing a large part of the tree’s crown in an indiscriminate way will result in wood fungal decay and mechanical damage from weathering to the exposed cut limbs and stems. The tree becomes weaker and the resulting shoots arising from the ends of the cut stems or branches will be weakly attached to the rest of the tree. Large, heavy sucker shoots invariably break away from their weak attachments creating a hazard to people and property. Topping trees makes them more hazardous.