Landscape Architect Articles

LSMP Tree Care September 200409-01-04 | News

Fall Maintenance Practices

By Ron Kujawski, University of Massachussetts Extension,
Landscape, Nursery and Urban Forestry Program

Corrective pruning involves removal of dead, damaged or diseased branches and the elimination of limbs that may be causing structural problems. Examples of structural problems include branches that may be rubbing, those that are growing back to the center of the tree and those with abnormally narrow crotch angles.

Fall is a critical time in landscape maintenance. Cultural practices employed now will ensure a healthier landscape next spring.

Clean Up

In a year when rainfall exceeds the norm and humidity is unusually high, foliar diseases are prevalent. Diseases such as anthracnose can, over the course of the year, reduce the photosynthetic capacity of plants. With repeated occurrences of such diseases, the vigor of the woody plants will steadily decline. Hence, it is especially important to reduce the potential for severe infections in years following the high precipitation.

The key is sanitation. Many of the diseases overwinter on leaves and stems of plants. These plant parts serve as a reservoir of fungal and bacterial spores (inoculum) for future infections. If conditions are favorable next spring, these fungal or bacterial spores can reinfect trees, shrubs and herbaceous plants. Therefore, as an important component of integrated pest management and plant health care programs, it is essential that infected plant materials be removed and destroyed in the fall. This means raking up the leaves, cutting down infected stems of perennial plants and pruning out the disease infected branches and stems of trees and shrubs.

Pruning

Fall offers an excellent opportunity to do corrective pruning. Normally, pruning is a growth-stimulating event. Since trees and shrubs are for the most part dormant now, this should not pose a problem. Also, the selective and targeted type of pruning involved is less likely to stimulate growth than is a general shearing type of pruning. As leaves drop from deciduous woody plants, it is easy to survey and detect defects in trees and shrubs. Canker formations, rubbing branches, splits and cracks in wood are apparent when not obscured by foliage.

Nutrient and Water Management

Research in recent years has shown that the nutrients supporting spring growth in woody plants are those that were taken up in the previous year and stored over the winter. One conclusion of that research is that late summer and early fall are the best times to apply fertilizer to woody plants in the landscape. This particularly applies to nitrogen application.

Water should be applied in fall starting in August and continuing through October. However, if an early freeze occurs when irrigation lines are still working, you run the risk of freeze damage before hardening.

It is widely assumed that fall applications of fertilizer will stimulate late season growth that will then be prone to winter injury. This is not true. At normal rates of application, fall applied fertilizers do not cause growth and in fact may help increase winter hardiness. Plant roots will continue to take up nutrients when the soil temperatures are above 40 degrees fahrenheit.

If organic fertilizers are used as the primary source of nitrogen, the earlier applications are better, since the rate of uptake is related to soil temperature. The usual amount of nitrogen applied to woody plants varies from one to three pounds per thousand square feet. The amount applied will depend on plant vigor and soil texture considerations. On sandy sites, lower amounts of nitrogen are applied to reduce the likelihood of leaching. Using slow-release fertilizers is also recommended on sites where leaching is a potential problem. Amounts of phosphorous and potassium applied should be determined by soil testing. The latter nutrients can be applied at any time of the year since they are more static in the soil than nitrogen.

Never mound mulch against the trunks of trees and shrubs. That can kill your trees. Instead, spread the mulch about three to four inches deep in a circle at least three feet in diameter. Any deeper can create shallow, vulnerable root systems. As the tree grows, extend the mulch to the edge of the canopy or dripline.

Fall soil tests should also be used to determine any corrections to soil pH. If limestone is needed to raise soil pH, this is an excellent time to make such applications. The combination of precipitation, melting snow and freezing/thawing events facilitate the movement of limestone into the soil. Winter survival of woody plants depends to a large degree on ample soil moisture levels in early fall. When soils are dry in late summer and early fall, water should be applied once every week or so, depending upon soil moisture levels, through October.

Mulching

Fall is a good time to apply mulches or renew mulches around trees and shrubs. Organic mulches such as bark nuggets, pine needles or composted wood chips are preferred because they help to establish a soil profile similar to that of the natural habitat of woody plants. The existence of this natural habitat with the addition of a significant organic layer on the surface of the soil accomplishes several things. For one, it buffers the soil from extremes in temperature and moisture levels. It also diminishes competition from other plants by retarding their growth or preventing their establishment in the vicinity of the trees.

Organic mulches will, over time, decompose to humus. In the process, nutrients are slowly released to the soil and are available for uptake by the plants. Where mulches are routinely maintained, the need for additional plant nutrients may not be necessary.

Organic mulches also serve as nutrient sources for a diverse community of microorganisms. These microbes benefit the health of the trees and shrubs in a variety of ways. They help make available phosphorus and other mineral nutrients, antagonize disease-causing fungi and bacteria and maintain soil fertility. A layer of mulch that is no more than three inches deep is best.

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Non-Natives Need Special Consideration

Cold injury varies with the plant species. The geographic range of native plants is determined by extreme temperatures and not by average temperatures. Therefore, the biggest problems are going to be seen in trees that are non-native. However, you can still see examples of native trees planted in urban or suburban landscapes where soils and environmental factors are vastly different from their normal habitat. Most woody ornamentals such as dogwoods are non-natives, and will therefore be more affected by extremes in temperature that are not consistent with their original growing areas.