Living with trees: Essential garden care and maintenance

By Linda Bell
Viewpoint Staff Writer

When we look at the enormous limbs and girth of many of our mature trees, many of whom have lived almost a century, we don't think of them as really vulnerable-especially to things that we do. Though none of us would take a chain saw to our favorite tree, we do injure their bark with lawn mowers and weed whackers or dig trenches which sever large sections of the roots that supply the materials essential to their growth. At times these actions have immediate results, but more often they accumulate unnoticed until the tree is weakened enough that a disease is able to invade. A healthy tree can usually wall off damaged or diseased tissue, but repeated damage or infections eventually leads to decline and death.

For example, though Dutch elm disease can infect healthy trees, it is usually spread through trees with dead branches and compromised health. If you are concerned that a branch of dead leaves in an elm mean it has Dutch elm disease, double check to see if their death may be due to a broken limb or to squirrels chewing off the bark before the section of dead leaves.

Here are some ways to lessen the impact of our gardening activities and everyday life and so help maintain healthy trees.

Pruning
Poor pruning cuts are a major avenue for insects and disease. To remove a limb you should use three cuts (see drawing). The first two cuts remove the weight and stop the branch from ripping off the trunk and creating a large, jagged wound. The final cut starts just past the bark ridge (a wedge of rough bark) and angles down to just beyond a usually, slightly swollen area called the branch collar, a natural zone for closure. The old practice of cutting a limb off flush with the trunk leaves the cut open to decay.

Irrigation
When installing an irrigation system, consider surface drip lines or soaker hoses. They are water efficient and do not disturb tree roots. If you use a buried irrigation system minimize the amount of root damage by using a few, well-placed trenches. Most trees, especially in areas with clay soils, have shallow root systems that extend well beyond the trees' canopy. This extensive mat of roots anchors the tree and harvests essential water and nutrients. The feeder roots that do most of the harvesting are within the first 8-16 inches. Trenching, especially if it encircles the tree near the trunk, can destabilize a tree, lead to die back, and even death.

Lawns and planting beds
If you are installing or revitalizing a lawn, a low impact method is to aerate the soil by removing plugs and rake in the seed. Rototilling can destroy the shallow feeder roots and send your tree into decline. It is best to keep grass and any plantings 1-1 1/2 feet from the base of the trunk and set sprinklers so they do not spray the trunk. This reduces persistent moisture that can cause fungal infections and rot. It also reduces trunk damage from lawn mowers and gardening activities.

Pathways and patios
Direct your foot traffic to pathways, so you lessen soil compaction. Foot traffic, especially on wet soils, compresses surface soil particles and eliminates air exchange and water percolation. Without water and air exchange, roots and the soil organisms that release nutrients in organic matter begin to die. Water sheeting off compacted soil creates a drought situation for tree roots at the same time that our gutter is filling with water.

An alternative to excavating paths is to establish them at ground level and cushion the soil with mulch, decomposed granite, or bricks set in sand or gravel. Elevated decks or modular patios composed of alternating blocks of ground cover and pavers set in sand have a lower impact on nearby trees.

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