Beverly Shaw
Master Gardener
Purdue University







Question and Answer

Q. My husband and I planted gallon-sized azalea plants last spring. Should they be pruned this year? If so, when and how much? We understand that they are an acid-loving plant. Since sulfur is acidic, can that be used? Thank you. -- Deanna Freeman

A. Typically, newly planted shrubs do not need much pruning except to cut out dead wood, which you can do at any time during the year. Improper pruning can cause a lack of blooms, so it's important to prune immediately after flowering. Pruning later in the year can result in pruned-off flower buds.

Azaleas and rhododendrons require cool, moist, acid soil with a pH of 4.5 to 5.5. They like a 2-3 inch layer of mulch. Mulch derived from pine needles, peat moss and oak leaves add to the acidity of the soil as they decompose. Water them well during droughts and just before dormancy and protect them from strong winter winds.

Our soils vary in whether they are naturally acidic or alkaline. Most plants grow well with a pH of 6.5 to 6.8, meaning that the soil is slightly acidic. A pH of 7 is considered to be neutral, and values greater than 7 are alkaline.

Alkaline soils are not desirable for growth of common garden plants and turfgrass. When soils have a high pH--greater than 7.2--the amount of available nutrients in the soil is limited. Nutrient deficiencies caused by alkaline soils will appear as a yellowing of leaves.

The only way to determine your soil pH is to measure it by doing a soil test. If the test indicates that soil is alkaline, you can lower it by using elemental sulfur, iron sulfate, acidifying nitrogen fertilizers, peat moss and organic matter. Elemental sulfur is the most effective when you work it into the soil before you plant. Bacteria must oxidize the sulfur before it can lower the pH, and the oxidation process will take 3-6 months.

The amount of sulfur to add depends upon the initial soil pH, the soil type and the desirable range you wish to obtain. For areas where plants are already established, add no more than 5 pounds per 1,000 square feet at each application. This should be done when it is dry to avoid burning the foliage. Wait 4-6 weeks before adding more. This should be worked into the surface of the soil, if possible.

When making major pH adjustments of greater than one unit, you should check the pH every six months before adding more. Sulfur can burn plants easily if too much is applied. Iron sulfate will react more quickly than elemental sulfur, but you need to add about six times more to get the same change in soil pH.

Once the pH has been moved into the approximate range for growing plants, it will be good to use acid-forming type fertilizers to help keep the pH in the right range. These fertilizers produce an acid reaction in the soil. Acidic fertilizers include ammonium sulfate and ammonium nitrate. These will add nutrients, as well as lower the pH; however, avoid burning plants by adding too much. Follow label directions for fertilizer application. Peat moss and other composted organic matter will assist in stabilizing the soil pH, once it has been corrected, but should not be depended upon to make major pH adjustments. For garden areas, add a 2-4 inch layer to the soil surface and till to a depth of 6-12 inches. Organic matter also will aerate the soil and improve drainage.

Q. I have some fence plants and have had them for about three years. They have never bloomed. Also, I have a dogwood tree that hasn't grown too big. I have had it for several years, and it doesn't always bloom. -- Bonnie J. Enlow, Taslow, Ind.

A. Many "flowering" plants sometimes let us down by refusing to flower. The following causes apply to all plants, both indoors and out. It takes some detective work to figure out which applies to your situation.

Age: Many woody plants have a vegetative phase of growth, called the juvenile stage, in which the plant does not flower. Juvenility may last 2-3 years on some flowering shrubs or 5-10 years on certain trees. Plants with a juvenile phase include crab apples, flowering cherries, wisteria (which can require 15 years to bloom) and nut trees, among others.

Transplant shock is not a function of the plant's age, but of the amount of time it has been settled into its new home. Many plants will take a several years to become established. Patience is required as the plant puts its energy into root and leaf formation instead of flowers.

Pruning: Pruning a spring-flowering tree or shrub in the winter or early spring will remove its flower buds, which form in late summer and fall. Prune spring-flowering plants just after they blossom.

If Mother Nature prunes your woody, spring-flowering plant for you by killing it back to the ground, there will be no flowers. Some form of winter protection may be necessary if the plant is marginally hardy.

Light: Consider a plant's light requirements when choosing its location. A plant that requires full sun will flower poorly, if at all, in the shade. The flowering of some plants, including poinsettias, chrysanthemums and gardenias, is controlled by the number of hours of light and darkness that they receive each day.

Temperature: Some plants, including fruit trees, spring-flowering bulbs and ornamental landscape plants, require cold temperatures to induce flowering. A mild winter may not provide an adequate chilling period. Temperatures can also be too cold. Plants may survive the winter only to have their buds damaged by late spring frosts.

Nutrition: Excessive nitrogen fertilizer promotes an overabundance of leafy growth at the expense of flower formation. A balanced fertilizer, such as 12-12-12 or 6-10-4, ensures that your plants receive nutrition in the correct amounts.

Remember these possibilities when your plants fail to bloom. Think back to the weather and site conditions that may have affected them over the last year.

Link to Managing Pests in Home Fruit Plantings

A reader pointed out that the link to the Purdue publication "Managing Pests in Home Fruit Plantings" (ID-146) did not work correctly. To download a copy of this informative booklet, go to


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