Tree health

Garden Clippings for July 29, 2023

Like people, trees require nutrients to survive and thrive.  You and I feed ourselves several times a day, giving our bodies a constant supply of what we need.  And the better we eat, the healthier we are and the longer we live.  No guarantees.

Ditto for plants and trees.  The millions of plants on earth each have their own set of needs, mostly involving light, water, nutrients and air.

Trees and plants growing in the forest can usually find their needs met in adequate quantities and will live forever.  Even forest fires, floods and lightning can be part of creation’s intricate master plan.

Trees growing in the city have their own set of challenges.  Urban growth has thrown a monkey wrench in the lives of trees, and it is only within the last century that we have begun to understand how urbanism has negatively affected the growth of trees.

These days, landscape trees growing in urban environments are forced to grow in highly altered, compacted and disturbed soil, often with inadequate nutrients.  Even native trees, with all their benefits struggle growing in a non-native environment.

Horticulturists have responded to the call by arriving at several trees in variety that are suited for tough city conditions.  Examples are Ginkgo, Locust, Maples and members of the Prunus family.  We are also learning that by amending the growing conditions, several native trees can indeed thrive in unfavorable urban environments.

Researchers are constantly uncovering new truths, but so far it appears the two biggest challenges for trees growing in urban environments are soil compaction and nutrient availability.

In the realm of soil compaction, there is little homeowners can do to improve soil structure.  We can modify the topsoil, but we cannot modify the many feet of subsoil underneath.

Fortunately, nature is our best aerator.  In our corner of the world deep frost does wonders to add air to compacted soil, thus improving percolation.  There is now increasing evidence that soil and subsoil at a newly developed site improves on its own.  Time does heal all wounds.

Progressive cities with advanced building codes are increasingly calling on developers to mitigate soil compaction by adding drainage to prevent trees from suffering under waterlogged soil.  Another wise move is to leave sizable sections within development areas untouched, allowing space for mini forests.

If landscape trees in urban areas are not thriving, it may be a good idea to add fertilizer to promote vigorous growth.  For young trees, spreading granular lawn fertilizer over the soil surface will do the trick.  For newly planted trees, add liquid root booster at transplanting time.

For large well-established trees, drill holes into the ground about 8 to 12 inches deep and pour granular fertilizer in the holes.  Drill most of the holes at the drip line and space holes a foot or two apart.  Consult a professional to determine the type, timing, and quantity of plant food.   For medium sized trees, consider using tree spikes, designed to release fertilizer over time.