Tuesday, February 7, 2017

What's limiting your trees's growth?

What limits plant growth?

Have you ever experienced a tree or woody ornamental that just doesn't want to grow?  Overall plant health and vitality depend on several factors, and if just one is out of whack, you may end up with an under performing plant.

It begins in the nursery
Starting with a quality plant is key for long term success.  Occasionally there are breakdowns in how the plant is cared for in the nursery that can affect how it thrives in the landscape.  During production, if a baby tree is kept in a pot for too long it may eventually form a distorted root system.  If these conditions aren’t addressed, the deformed root system will remain with the plant for it's entire life.

One common root distortion that may form is circling roots.  Circling roots are roots that grow around the stem of the plant instead of perpendicularly away from the plant.  In the nursery this happens when young roots contact the side of the pot in which the plant is growing, and start growing along the outside of the container.  Circling roots can affect plant stability.  If these roots are in contact with the stem they can lead to a condition called girdling roots.  Girdling roots have the potential to cut-off portions of a stem’s vascular system, interrupting nutrient and water flow through the plant.

At planting
There is an old saying, “you only get one chance to plant a tree.”  While planting a new tree or shrub seems intuitively easy, there are some caveats to proper planting.  All woody plants should be planted so their root flare is  at grade level and exposed, not covered by excess soil or mulch.  The root flare is the transition zone between the trunk and the roots.  Buried root flares may result in bark damage which lead to vascular system issues.  Buried root flares may also lead to girdling roots.   Note, sometimes root flares are buried due to poor nursery practices.

It’s also important to dig a hole large enough for the tree/shrub.  Standards state digging a hole at least 1.5 times the diameter of the plant’s root ball. The larger the planting hole the better.  This is so newly emerging roots have an easy time of colonizing the native soil.  The more soil that can be loosened around a newly planted tree, the faster the tree will be able to become established.

Site, site, site
Matching the right tree to the site and site preparation is paramount to overall performance of trees and woody ornamentals.  Different species have unique light, soil, and water needs.  Let’s take our native flowering dogwood as an example.  According the USDA NRCS plant materials program: “Flowering dogwood is adapted to most upland sites but grows best on rich, well-drained soils on middle and lower slopes. It develops best as an understory species in association with other hardwoods.”  So, if we are to plant a flowering dogwood in a poorly drained clay soil in full sun, it goes without saying the tree will not be healthy vigorous specimen.

One major issue we run into, especially in our urban/suburban landscapes, is damaged soils.  During new building construction the top layers of soil, which forest trees roots thrive in, are removed.  What remain are compacted subsoils.  Compaction destroys soil pore spaces that air, water, and plant roots occupy.  This is direct stress on woody ornamentals, and one of the greatest reasons trees and shrubs fail to thrive in our landscapes.  Accompanying compaction in urban/suburban soils are also nutrient deficiencies, soil chemistry imbalances, and inadequate amounts of soil organic matter.

Another major issue for plants in our landscapes is water issues.  Too little or too much water is often the difference between green and growing plants or yellow and dying plants.  Combine improper watering with poor soils and you have a recipe for disaster.

All's not lost
Fear not.  While the issues we discussed may sound overwhelming the arboriculture industry has developed some innovative protocols and tools for mending these common problems.  Laboratory soil analysis, soil decompaction treatments, and root collar excavations utilizing compressed air-tools are just a few methods available to mend adverse plant growing conditions.  If you have a tree that just doesn't seem to be growing, call your friendly neighborhood qualified arborist for a thorough assessment.