Sunday, September 20, 2020

Some Planting Dont's

As we are moving into fall planting season it got me thinking back on some planting don’ts.  This was initially brought on by a sourwood tree that was planted here before we moved in.  Over seven years here it never got much bigger and for the past two years it was showing definite signs of decline.  I tried feeding it and acidifying the soil (it prefers a pH of 4.5-6) to no avail.  When it was finally dead this year I went to dig it out of the ground and found that I could lift it out of the soil with relatively little effort.  It turns out that even after over 7 years in the ground its roots never expanded outside the size of its original nursery container.  I suspect that the roots found it easier to stay within the original nursery mix rather than venture outward.  When I pulled it out of the ground there was very little soil left within the root ball.  Over the years the nursery mix broke down and dissolved away leaving nothing around the roots.

Here's my dead sourwood as it was
pulled out of the ground.

Sourwood trees usually produce deep lateral roots.  
Here the larger roots have circled back.  Also,
 there was little real soil within the root mass.

When planting a container grown plant you need to tease out some of the roots from the original container shape.  This is particularly important when dealing with a pot-bound plant.  In severe cases it may be necessary to cut the roots to encourage them to expand outward.  This was a case where it looked OK for a while.  Planting dos: the hole should be no deeper than needed so that its crown is just above the soil level.  The hole should be about twice as wide as original ball/container; and, back fill the hole with native soil, not more than half amendments, if any at all.  For compacted soils a wider hole is needed.  It also helps to make some jagged cuts to the sides of the hole rather than making it a smooth circle.  In this way when a growing root encounters the compacted soil interface it may be forced to penetrate it rather than just veering off to the side.  The goal is to get the roots growing outward and downward into the native soil-not to create a mirco-environment that the roots will never leave. Check out this link for more information on proper planting techniques.

Another thing to watch out for, especially in container grown plants, is circling roots.  These are thicker roots that reached the edge of the pot and curving around the edge of the pot.  Left uncorrected these roots will form a barrier to expansion of the trunk as the tree matures, eventually choking off the flow of sap up and sown the tree.  The best option is just not to buy a tree or shrub with circling roots.  If you already have one you can try to untangle the circling root, or it may be better just to cut it off for the long term health of the plant.

Sometimes the effect of poor soil contact is seen faster.  Because moisture moves from coarser to finer soils by capillary action, a container grown tree or shrub inserted into finer textured soils may dry out unless there is intimate contact between its roots and its new soil home.  This is because there is little tendency for soil moisture to migrate from the fine textured native soil to the coarser bark/peat moss/compost mix that the containerized plant comes in.  When planting container-grown plants I usually knock away a good portion of the planting mix to expose as many roots as possible and then put these roots in direct contact with the native soil.  I use the freed up planting mix as the ‘soil amendment’ to blend with the back fill.


The rounded crown of this once beautiful specimen has been
decimated to reduce problems with the power lines.  It's interesting that
the more upright trees (oaks, I think) located just a few feet back are not
interfering with the wires to the same degree.

Another factor that affects long-term plant survival is siting.  By this I don’t mean proper soil and light conditions, I am referring to location with respect to buildings and utilities, both above and below ground.  Planting big tree too close to a house can cause a multitude of problems ranging from root damage to the foundation and falling limbs to aesthetic problems like being out of scale with the house or blocking views.  Cultivars come in handy when working in a defined space.  These plants have predictable sizes and shapes thus reducing the effort to keep them the right size.  Utilities are another consideration.  You may get away with planting too close to them for a number of years, but when utility work needs to be done, your prized plants will be sacrificed for the sake of keeping the lights on or the water flowing.  Probably the most commonly encountered problem is planting large plants too close to overhead wires.  This conflict is often exasperated by the desire to have street trees and the first place we look to is the often too small strip between the sidewalk and street.  Utility companies publish guides and many communities have regulations about planting under utility wires [for example see this link from Baltimore Gas and Electric].  The general guidelines are to limit the mature size of trees and shrubs under wires to 25’ and not to plant larger materials within 25’ of the wires.  Larger plants should be located such that, when mature, their branches will not interfere with the overhead utilities.  Recommended plants will vary by region, but here in the Mid-Atlantic, good native candidates include Dogwoods, Redbuds and Hawthorns. 

This Bradford pear is starting to interfere with the power lines
and the lower branches on the street side have been damaged
by passing trucks.  This is just not a good location for a tree. 

Passing traffic is another factor to consider with street trees.  I had a Bradford pear planted too close to the road (planted by the city) that was repeatedly clipped by passing trucks and delivery vans.  It was also growing up into the power lines.  Perhaps the plan was that the Bradford would die or otherwise fall apart before it got to be much of a problem.  (Note that Bradford pears are proving to be invasive species as well as structurally unsound, and in my opinion are a very poor choice in any North American landscape)

The root flare is probably about 6" below the top of this volcano.  
An ideally planted tree would have no mulch within 3" 
of the root flare and the flare would be only an 
inch or two above the native soil level.

Mulch volcanos.  Fortunately these are showing up less often, but still many trees get this treatment.  Mulch mounded up and covering the root flare at the base of a tree will encourage bark rot and, more perversely, surface roots.  These are roots encouraged to grow in the loose, moist mulch, rather than deeper in the soil.  They are more susceptible to physical damage, can  dry out easily and many cases will circle and cross close to the tree truck.  As the tree matures, these crossing/circling roots choke off the main trunk from expanding outward, weakening the tree after 10 or 15 years of blissfully ignorant growth.

By putting a little extra thought into site planning and in helping plants get better rooted you can avoid a lot of disappointments in your long-term landscape investment.