The Ericaceae plant family includes rhododendrons, azaleas, blueberries, heathers and other popular home garden plants. All members of this family flourish in acidic soil. Planted in non-acidic soils, these plants are susceptible to iron deficiency and stunted growth, advises the University of Illinois Extension's Sandra Mason. Ericaceous plant foods are fertilizers that help make soils hospitable to acid-loving plants.
Determining Soil pH
Ericaceous plant foods affect soil pH balance. Acid loving plants are happiest with a pH range between 4 and 5.5, says University of Missouri Plant Diagnostic Lab director Manjula V. Nathan. Most garden supply stores carry soil pH testing kits. Testing the soil will determine its pH. Adding sulfur or iron sulfate lowers high pH. Retesting the soil four months after applying sulfur or four weeks after applying iron sulfate will determine if the pH is suitable for planting.
Suggested Plant Foods
Many brand-name plant foods are available for ericaceous plants, says Nathan. Use them at the manufacturer's recommended rates. An alternative feeding method is to apply a balanced fertilizer of 10 percent nitrogen, 10 percent phosphorous and 10 percent potassium in the spring. Fertilizer labels have large numbers indicating their amounts of those ingredients in that order. Soil with enough phosphorous and potassium benefits from an application of plain nitrogen-based plant food, like ammonium sulfate, at the rate of 1 lb. per 100 square feet.
When to Feed
Feed the plants a single application of the the appropriate plant food in the early spring. Feeding any later than August 1st can harm them, advises Nathan. Late feeding may encourage growth during winter, the plants' normal dormancy period.
Applying the Plant Food
Plants of the Erica family have shallow, fibrous root systems, says University of Connecticut horticulturist Edmond L Marrotte. Heavy fertilizer applications can be damaging. Follow your plant food manufacturer's recommendations for the lowest rate of application.
Ericaceous plants need plenty of the minerals iron, zinc, copper and manganese. They are especially are susceptible to iron and manganese deficiencies. New foliage on iron-deficient plants is yellow, often with green veins. The best food for these plants is an application of iron sulfate/water sprayed on the foliage in a concentration of 1 ounce of sulfate to 1 gallon of water. A permanent solution is to apply between 1 and 2 lbs. of iron sulfate to each 100 square feet of soil, mixing and watering it thoroughly.
Foliage yellowing on manganese-deficient plants occurs on older leaves first. Soil and plant tissue testing are the only methods of identifying this problem. An application of 1/2 cup of Epsom salts per 100 square feet of soil well mixed and watered around deficient plants will correct the condition.