The Pennsylvania State University ©1997

Summer Plant Care

May 15, 2000
Summer is a time for building, maturing, and storing in the plant world. The new stems and foliage have expanded and leaves are functioning at full capacity with their manufacture of sugars and carbohydrates that will be stored to support growth and reproduction next season. The care we provide now will impact plant quality next year.

All too often consumers tend to water just the backfill material in the hole while the dry site soil pulls water from the root system. It is recommended that water be applied to the surround site as well as the backfill.

Proper watering can become a balancing act between not adding enough or adding too much and drowning the existing root system before it has a chance to establish. Optimum moisture levels can be maintained in the surrounding site with soaker hoses or overheard irrigation as needed.

Next to water, mulch and its proper application are key factors to the survival and success of any planting, especially during the drier summer months. Any material that reduces the loss of water from the soil surface could be considered for mulch. However, aesthetics generally dictate that we consider coarser organic materials with a dark brown color.

To be effective the mulch material should be applied over the entire root zone. We frequently place mulch under the spread of the plant, but fail to use it on the outlying soil where roots will penetrate as the plant establishes. Surrounding soil should be mulched as well to retain adequate levels of moisture to support root expansion and growth.

A two to three-inch layer of most organic mulch material will be highly effective in the elimination of weed growth while slowing the upward movement of moisture and its loss from the soil surface. Thick applications of mulch over the root system should be avoided because it has a tendency to smother the roots.

In addition, the mulch should never be piled around the stems or trunks of plants. This practice still appears in a number of locations and will ultimately cause considerable damage to the mulched plants. Under these conditions there is a great potential for bark rotting where it comes in contact with the mulch. Some thin barked trees may actually root into the mulch, or rodents can feed on the bark that is covered under the layer of mulch.

The use of the landscape fabrics or geotextiles in conjunction with other mulches is still a questionable practice. If used under organic mulch materials there is a potential problem with weed roots penetrating downward through the fabric and becoming well established. There aren’t too many indications that the fabric increases the effectiveness of a good layer of organic mulch. However under the layers of inorganic mulch materials like river rock or gravel, the fabric does have an application. In these instances the fabric does seem to prevent weed germination while allowing water to penetrate to the soil below.

Summer fertilization is generally a questionable practice, but it does have a place on many annual and herbaceous perennial crops that need to be growing actively. Woody material will benefit from light applications of water soluble fertilizer to maintain plant quality throughout the summer. To be avoided however, are substantial applications of the slow release materials once the growth has matured and buds are set. Such products used in higher rates will meter out sufficient nitrogen to trigger an additional flush of growth later in the season when adequate moisture becomes available.

Summer pruning is another practice that should be kept to a minimum. Removal of a branch or stem for cosmetic reason will do the plant no harm. However significant removal of foliage in the summer will reduce the plants ability to produce needed food materials for winter survival and growth next year. Some gardeners will use this technique with great success to slow and contain the growth on overly vigorous plants and it does work when you understand the principles and appreciate what balance is needed to retain sufficient leaf cover for food production during the remainder of the season.

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**Dr. Robert Nuss is a horticulturist at Penn State. He coordinates all extension horticulture programs. He has bachelor’s, master’s, and doctoral degrees in ornamental horticulture and has been on the Penn State faculty since 1966.