Dutch elm disease is the main issue when caring for elm trees.  All maintenance practices must be done with this threat in mind.

Soil Improvement

Over millions of years, elm trees have evolved to thrive in a specific type of soil.  When an elm is transplanted into a new environment, the soil is rarely ideal.  The make-up of urban soil (moisture levels, mineral content and composition of organic elements) is often entirely different from the soil in which elms grow naturally.  To find out how to make your soil more natural, click here.

Fertilizing

Elms should be fertilized once or twice a year.  However, not just any fertilizer will do and using the wrong type of fertilizer can actually increase the chances that your tree will contract Dutch elm disease. For more information about fertilizing an elm tree, click here.

Pruning

Pruning is one of the most important ways we can help an elm tree.  Because of the threat of Dutch elm disease, special considerations must be taken into account.

Unlike many other tree species, pruning must be done at a very specific time of year. Because open wounds attract the elm bark beetle (the major vector for Dutch elm disease), pruning should never be performed from about mid-April to late-July.  In fact, some communities have bylaws to this effect.  Also, due to presence of a variety of fungal spores in the fall, if possible, pruning should be avoided.  This leaves early spring as an ideal pruning season.  With the growing season to follow, the tree has ample time to close the wound and regain its vitality. 

Mature deciduous ornamental trees such as elms should be thoroughly pruned once every three years with annual minor pruning.  In areas where Dutch elm disease is present, more vigilance is required to allow timely removal of dead or dying branches.  If a tree is noticeably slow to bounce back from a pruning session, less frequent pruning may be in order.  (See: How to Prune a Tree)

Lawn Care

In natural settings, the ground around large shade trees is covered with leaves. As the leaves decompose, they release nutrients which the tree needs. Not so in our cities where are trees are surrounded by grass. The grass actually competes with the tree for water and nutrients.  

Scatter fertilizer around a tree and you will end up with very healthy grass. Tree food stakes inserted into the ground release nutrients below the grass layer. Use fertilizers specifically designed for shade or elm trees.  Also, take care when mowing.  Lawn mowers can damage a tree.  Better yet, avoid the problem by keeping the grass back from the base of the tree. A buffer zone of loose soil or mulch is ideal. 

Watering

In an elm, the tips of the roots are usually located outside of the weeping or drip line.  This is the outermost extent of the crown of the tree.  Therefore, sprinkling water onto the trunk will have little or adverse effect on the tree's health.

It is important to remember that grass and other vegetation compete with a tree for moisture.  As a result, sprinkling is not a very efficient method of watering.  Firstly, there is extensive evaporation, and secondly the grass absorbs a large percentage of this water.

A preferable method of watering is to soak the ground outside the weeping line with a hose.  There are also special devices that allow you to apply moisture directly into the ground near the roots.

It is important to allow the soil to dry in between waterings.  If the soil is constantly wet, it can easily become compacted, hindering gas exchange with the air.

Examine nearby trees:  If other trees in your area show signs of drought, your tree may be next.  Often other species, such as maples, show signs earlier than elms giving an early warning signal.

Physical Obstacles  

Due to the sheer size of a mature elm, things tend to get in its way.  The easiest way to avoid conflicts with physical obstacles is to plan around them.  This means care when planting.  Elm trees should be planted at least 5 metres (15 feet) away from houses and never under utility lines. The result will be frequent and costly pruning.

Construction

When doing construction around an elm tree, care must be taken to avoid cutting the root system.  It is difficult for the tree to close root wounds.  Cutting roots can leave the tree vulnerable to attack by a fungal disease such as Dutch Elm Disease.  If cutting the root is unavoidable, attempt to make clean cuts exposing as little surface area as possible. 

Disposal

A dead elm tree is a threat to all the other elm trees in the neighbourhood.  Because dead wood is an ideal breeding ground for the elm bark beetle and the DED fungus, disposal of dead limbs and trees must be done properly and quickly.

If you have a dead elm, first remove the major limbs and proceed to cut down the tree.  Remember taking trees down is not a job for the amateur. (See: How To Remove A Tree). Call a tree removal company. Some municipalities offer disposal services for large trees.  

Wood should be burned immediately. It should not be stored. Some communities have strict by-laws prohibiting the storage and transportation of elm firewood.  If there is insufficient space for burning, the wood can be buried.