Solving Plant Problems
Craig S. Oliver and J. Robert Nuss
Reviewed by J. Robert Nuss, Professor of Ornamental Horticulture
The soil test analysis provides an accurate measure of the chemical elements available in the soil for plant growth. Based upon this analysis a recommendation can be written regarding the required amount of fertilizer and soil modification materials needed to obtain optimum plant growth.
The soil test does not reveal the nature or cause of physiological plant problems which directly relate to the ecological (environmental) conditions in the locale where you live. To diagnose the problem, use a checklist. Corrective measures are outlined in the section entitled RCultural Recommendations.
Poor Soil Structure - The physical condition of the soil is extremely important for optimum plant growth. When you look at your soil you see structure. The lumps you see are made of several soil particles clumped together. The common materials holding them together are water and organic matter. Good structure is essential if the soil is to get the proper amounts of air and water to provide for optimum plant growth.
Light sandy soil can be improved by mixing peat with the soil to be used for planting. A ratio of 1 part peat to 3 parts soil by volume should be sufficient. The peat will provide the needed organic matter and improve the water holding capacity of the soil.
Soil modification in heavy soils is a difficult task. Often the best solution is to replace the soil removed from the planting hole rather than spending the time and energy to improve its physical condition. If the soil located on the sight must be used, it would be advisable to mix equal parts of peat, sand (perlite and similar materials can be substituted for sand) and soil to use for backfilling in the planting hole.
Unfortunately, little can be done to improve soil structure once the plant has been planted. Soil modification should be done at the time of planting.
Winter Injury - Injury to plants often occurs when plants are exposed to strong winter winds and sun. Usually the plant species which are most often affected are rhododendrons and other broadleaved evergreen species. The injury which results is caused by excessive moisture losses through the leaf tissue. This moisture loss which is called transpiration is common in all plants, but when the soil is cold and the roots are inactive, water is lost faster than the roots can replace it. To prevent such difficulties:
1. Plant broadleaf evergreens and other tender plant species in spots protected from wind and sun. Avoid southern exposure.
2. Provide evergreen plants with ample moisture, both before the ground freezes in the fall, and during the growing season. In late fall (November) water the ground heavily to prevent its drying out during winter.
3. Mulch evergreens when growth has hardened in the fall (after non-evergreen plants have dropped their leaves). Mulching will insulate the soil from sudden temperature changes, reduce the depth to which freezing takes place, and reduce the time that the ground is frozen.
4. Protect sensitive plants with a windbreak or unshade. Place the windbreak on the windward side to moderate the wind and the sunUs rays.
Drought Injury - During the past three to four years, drought injury has been excessive in all areas of Pennsylvania. Thorough watering every 10 to 14 days, mulching plants with 2 to 3 inches of organic material (peat, well-rotted sawdust, etc.), and keeping the plants in a generally good state of health will eliminate drought injury.
Over-Fertilization - Too much fertilizer is just as bad as not enough. Excessive fertilizer applications will lead not only to weak spindly growth, but can also result in root injury. Fertilize according to soil test recommendations. Soil test kits can be purchased from your county agricultural agent.
Frost Injury - When plants harden-off incompletely in early autumn, early fall frosts may kill flower and leaf buds. In this condition, the buds will also be killed by sudden cold spells in November and December. During the first warm days of spring, temperature hardiness is quickly lost by some of these buds as they break dormancy. A severe frost following this loss of dormancy can cause the flower or parts of the flower to die and leaf deformation.
Harden plants off by moving mulch materials two to three inches from the base of the stem in mid-August. This will allow time for bark and wood to dry and mature before early fall frosts can cause injury.
Iron Deficiency - The shallow rooted Ericaceous plants (rhododendrons, azaleas, leucothoe, mountain laurel, etc.) develop chlorosis when anything interferes with absorption of iron through the roots, or when iron in the plant is in an unavailable form.
Physical causes of chlorosis are incorrect cultivation of the soil which destroys some of the feeding roots; insufficient mulch, which allows the soil to heat and dry out extensively and injures feeding roots; sandy soil with too little organic matter to retain moisture; or poorly drained soil that has too little oxygen.
Chemical causes are too much lime, which raises the alkalinity so the iron in the soil is in a form unavailable to plants; or an actual deficiency of iron in the soil.
If chemical causes are responsible, spray young foliage of nearly mature size in the spring with a solution of chelated iron or ferrous sulfate (1/4 of one percent or 1/4 teaspoon to one pint of water). Although this only is a temporary correction, it will restore green color quickly in young leaves.
For permanent correction of the chlorotic condition, a complete soil analysis should be made and the pH adjusted according to the recommendation.
The application of chelated iron or iron sulfate to the soil produces a longer lasting effect than spraying the foliage. Repeated applications are often necessary to maintain attractive green foliage.
Weed Killer Injury - Fumes or minute droplets of chemical weed killers can drift from lawns to shrubs several feet away and cause distortion or curling of leaves. When weed killers are used, careful attention must be given to spray drift. Avoid spraying on a windy day. A sprayer that has been used for weed killers should never be used for insecticides and fungicides.
Insufficient Light - Plants growing under heavy shaded conditions often will develop weak spindly growth and flower poorly. Select plants for shaded areas that will tolerate low light levels.
Where trade names are used, no discrimination is intended and no endorsement by Cooperative Extension is implied.
J. Robert Nuss
Department of Horticulture
Penn State College of Agricultural Sciences
103 Tyson Bldg., University Park, PA 16802