Look before you plant landscape trees

Successful landscape plant selection and establishment begins with a thorough site assessment.

Select flood-tolerant trees for sites where water ponds after heavy rains. Photos by Bert Cregg, MSU.

Select flood-tolerant trees for sites where water ponds after heavy rains. Photos by Bert Cregg, MSU.

The phrase “right tree - right place” has become firmly entrenched among landscape professionals. While the notion of matching trees and other landscape plants to their intended site seems intuitive and obvious, identifying which site factors are most critical for successful plant establishment may not be as clear. Plant performance is related to an array of above-ground and below-ground environmental factors; many of these are discussed in detail in Michigan State University Extension bulletin E2996, “Abiotic Plant Disorders.” A few site conditions, however, consistently prove to be especially critical for initial establishment and long-term success of landscape plants. These factors are essential to any pre-plant site assessment for landscape professionals and homeowners.

Site drainage

Trees and shrubs vary widely in their tolerance of flooding or poor drainage. Many bottomlands species, such as cottonwoods, sycamores and red maples, can often tolerate sites that flood periodically. Other species, such as hickory, sugar maple and many pines, will grow poorly – or will not survive at all – if planted on sites that flood or have poor drainage. Changing site drainage is usually difficult or impossible, so the best strategy for poorly draining sites is to select trees that are adapted to wet conditions.

What to look for

Make a mental note of areas on your property where water tends to pond after heavy rains. In some cases, it may be possible to relieve flooding issues by redirecting downspouts from your house. If you are assessing a new property or are unsure of the drainage patterns, conduct a simple percolation test following these steps:

  1. Dig a hole 18-by-24 inches deep.
  2. Fill hole with water to the top and let stand for at least an hour to pre-wet the soil.
  3. Refill the hole to the top with water.
  4. Allow the hole to drain for at least one hour. A longer period of time (two to three hours) will give a more accurate reading of average percolation rates.
  5. Determine average drop in water level per hour.

Interpreting soil percolation test results

Drainage rate

Drainage class

Less than 0.5 inch per hour

Poorly drained: Suited to wet site species only.

0.5-1 inch per hour

Moderately well-drained: Acceptable for many species including wet site species.

More than 1 inch per hour

Well-drained: Suitable for all species including sensitive species.

Adapted from: Smiley, E.T. and T.R. Martin. Soil Drainage: Analysis and Treatment Considerations, Bartlett Tree Research Laboratories Technical Report TR-75.

Alkaline soils

Soil pH is a measure of the relatively acidity of a soil. As a general rule, a soil pH of 6.5 is considered optimal for most plants, though many plants can tolerate higher pH. A few plants, however, such as red maple, pin oak, azaleas, rhododendrons and many conifers are very sensitive to alkaline soils and will become chlorotic if soil pH is too high. This sensitivity is usually related to reduced availability of iron and manganese as soil pH increases.

What to look for

For existing plants, leaf yellowing (chlorosis) is the most common symptom of a pH-related nutrient problem. Oftentimes the leaf veins will remain green while the rest of the leaf becomes yellow. For new planting sites or to diagnose problems on existing plants, soil pH is included as part of the soil test analysis provide through MSU Extension’s Soil Test Self-Mailer.

It is also relatively easy to determine soil pH using a pH meter, which can be purchased through many garden centers or online catalogs. To measure soil pH, collect a representative sample of soil, place the sample in a cup with distilled water (one part soil to one part water), mix well and allow to settle for 15 minutes. Determine the pH of the solution following the instructions provided with the meter. A key point to remember is to calibrate the meter prior to each use.

Red maple leaves showing a progression of becoming chlorotic as pH becomes more alkaline

Red maples are sensitive to soil pH and will become increasingly chlorotic as pH becomes more alkaline (bottom to top in these photos).

Shade

In native forests, trees such as hemlock, beech and hornbeam have evolved to grow under the shade of other trees. Other species such as aspen and larch have evolved to colonize open areas and are very shade-intolerant. While shade-tolerant trees can often grow well in exposed conditions, the opposite is not true and shade-intolerant trees will usually decline quickly when planted in low light environments.

What to look for

There are few hard and fast rules regarding how much sun exposure shade-intolerant trees need. Often, however, their growth rate and overall vigor will be proportional to the amount of light they receive. Observe the sun and shade patterns of your yard and avoid shade-intolerant trees if they can’t get at least six hours of direct sun per day. To help assess the sun and shade patterns of your yard, there are several online tools and apps available, such as Find My Shadow, that provide a graphical representation of daily shade patterns based on your location and time of year.

Dr. Cregg’s work is funded in part by MSU’s AgBioResearch.

Related Articles