How to Grow a Good Street Tree

What Does it Take to Grow a Good Canopy Tree?

The Forest Board in 2007, with the Urban Forestry grant, resolved to address two main problems that caused significant mortality in new plantings:

  •  Injury to the low trunk, caused primarily by mowers.  With the best of intentions, people could not avoid banging against trees.  These early low wounds on thin new bark forever change the growth potential of the young tree.  The solution was to build a sturdy hardware cloth cage with at least a four foot diameter around the tree.  This also held mulch in place around the tree, and helped reduce weed competition.

  •  Poor establishment in the first year from erratic watering.  Trees need steady consistent moisture, drip irrigation, to establish, and if watered well in the first year, are thereafter much more tolerant of periods of drought.  Thus, we discovered the Ooze Tube, which also shades the ground around the tree in the first year. 

With these interventions, NONE OF THE 2007 GRANT TREES DIED AND MOST GREW BEAUTIFULLY!  In fact, after planting more than 100 trees in the past 5 years, only 7 trees have died, two from human vandalism and several due to poor condition from the nursery

The other Key to Successful Planting:  Site Preparation

Urban soils are notoriously bad for trees. Some have measured density greater than concrete.  In most of the Audubon Park area, we started with an excellent deep well-drained soil type called Crider Silt Loam.  But construction and roads and heavy equipment and cars all create a problem called “compaction”.  For existing trees, these processes crush the roots; for new plantings, compaction reduces the pores in the soil that deliver oxygen to roots and causes poor drainage, so soils become boggy and saturated.  Tree roots actually drown before they rot.  Some sites are also full of debris – asphalt and old buried concrete. One homeowner recently discovered a long buried sidewalk.

In 2008, the Forest Board began collaborating with the Limbwalker Arborists on using “air-knifing” to decompress and restore urban soils.  This process uses compressed air to re-inflate the air pores in soil, and also breaks through the cemented subsoil layers called “hardpan” so that drainage improves. The air knife can identify obstructions in the site – remnant roots, stones and debris, and doesn’t damage roots from surrounding trees.

The Forest Board also established a goal of a minimum of a 10 x 10 square foot area as the root zone for any canopy tree.  The area that is airknifed is about 4 x 4 square foot.  This site approach & preparation creates excellent deep sites without an edge to the planting hole and allows a large enough volume of soil to support long-term growth.

Every tree we plant should have an ooze tube for the first year, and an hardware cloth cage. You've seen these around!  And will notice these in many pictures of smaller trees.

There is a saying that the best time to plant a tree was 20 years ago.
The second best time is now.

New Trees

The Garden Club has been planting for over 20 years, and The Forest Board and Garden Club as partners are still planting now.

Since 2005, the Forest Board, with funding from the Garden Club and a grant from the Kentucky Division of Forestry and cost-sharing with homeowners, has planted over 120 trees.  This includes 87 canopy trees, 11 mid-size trees (for under overhead wires), and 22 ornamentals. Sixty-five trees were canopy street trees, including various oaks, tulip poplars, basswoods, elms, and London planes.

What is a Canopy Tree ?

A canopy tree can be defined as a tree in the dominant crown class, meaning that it receives sunlight from all sides (that is, it grows tall and straight and fast enough to hog the sunlight.)

These are our sugar maples, ashes, oaks, sycamores, London Planes, and tulip poplars. Most of the ornamentals, including the dogwoods that are so important in Audubon Park, are understory trees. These trees, redbuds, serviceberries, silver bells, do most of their growth and bloom before the big trees leaf out, and give us that wonderful relief that Spring is here. Many of the ornamentals prefer filtered shade, and their lives are shortened and stressed when they grow in full sun.

Co-dominant crowns of trees receive light only from the tops, and this can occur when trees that are all the same type and age are planted too close together and develop a spindly habit, stretching too tall for their diameter to compete for the sun. Red maples are intermediate trees and are shade tolerant. Intermediate crowns receive very little direct sunlight, and truly suppressed or overtopped crowns receive no direct sunlight. Many true dominant Canopy trees are so shade intolerant that they gradually die when they are overtopped for any length of time.

Other trees prefer filtered shade and spread to fill in under the dominant canopy trees, and still other trees do most of their growth in the spring under the dominant canopy, before they are shaded out. Many of these trees are the ornamental spring blooming trees, like dogwoods and redbuds which we plant in abundance.

Choosing the best Tree

Every fall and spring, the Forest Board accepts requests for tree planting, and consults with homeowners to help evaluate the site and choose the best tree.  Generally, we recommend that homeowners choose younger trees – the trees are less expensive and establish more readily; larger trees have a greater adjustment and more stress in transplanting than smaller trees.  We maintain relationships with a number of tree sources to try to expand the availability of choices and work with local nurseries to expand diversity in tree species.  We hope to assist 10 homeowners per year (spring and fall) to establish new shade trees.

You can also learn more about different kinds of trees from the care pages about specific species and from a numbers of sites on-line.

To reach a member of the Forest Board, you can call Betty Weise, the current Forest board Chair, at 502-637-3037 or attend a Forest Board Meeting on the second Wednesday of each month (except December.)  You can also join us in work days at the Parks, where we teach pruning and tree care and give people a chance to practice their pruning skills.

Anne Bobigian,
Feb 14, 2012, 5:25 PM
Anne Bobigian,
Feb 14, 2012, 5:25 PM