Rhododendrons have a few requirements: excellent drainage, a soil pH between 4.5 and 6.0, and protection from hot afternoon sun.

Site: Plant the rhododendron out of the wind and in dappled shade, preferably from a high cover of limbs that will give filtered shade all day. Some varieties will take a few hours of direct sun in the morning, but most need protection from the intense Southern sun. Trees should be tall enough to be limbed up so the shrubs will get plenty of light. These trees will cut the force of drying winds in winter as well as summer.

Drainage is improved by planting on a slope – a northern slope is preferable to a southern slope. When using rhododendron in a foundation planting, avoid southern exposures. The best place to plant is on the north or east side of a building.

Soil: The soil for these woodland plants must be well-drained and high in organic matter. Organic matter improves drainage in clay soils and will increase a sandy soil’s ability to retain water and nutrients. Add about 4 inches of pine bark over an area two to three times the area to be covered by the branches of the plant you are setting. Mix it into the top 6 to 8 inches of soil.

Planting: The best time to plant is in the fall when the roots have a period to acclimate and prepare for early spring growth. The plant will require a good bit of water during the first year of establishment.

Mulch: Mulch helps to retain soil moisture around the roots. As it breaks down, mulch provides nutrients for the shrubs and improves the soil texture. Furthermore, it aids in weed control, eliminating the need to disturb the roots through weeding. A 2- to 3-inch layer of compost, pine bark or pine straw is excellent mulch. Extend the mulch well beyond the outermost branches of the plant. Pull mulch away from the main stem to help prevent disease.

Watering: Rhododendrons are shallow-rooted plants and require irrigation during dry periods. This is especially true of those planted in the preceding spring. Rhododendrons planted in warm weather in sandy soils may require watering of the root system twice a week during the first year. Newly planted rhododendrons require regular watering during dry spells for the first several years.

Pull back a small area of mulch beneath the canopy of the plant and check the soil moisture level. When the soil feels dry, wet it to a depth of 8 to 12 inches. Use soaker hoses or drip irrigation to slowly water the base of the plant.

Be mindful that rhododendrons in waterlogged soils will decline and become susceptible to root rot diseases. It is important to reach a balance between regular, deep watering and good drainage to promote a healthy plant.

Fertilizing: With proper soil preparation and mulching, very little fertilizer is necessary – particularly for the older, established plant. Do not fertilize rhododendrons at planting; newly planted shrubs can be fertilized after they become established.

Allow newly planted shrubs one to several months, depending on their size, to begin establishing their root system in the landscape soil before applying fertilizer. Once the shrubs are established, have a specific reason, such as increasing the growth rate or correcting a nutrient deficiency, before deciding to fertilize. Maintaining a mulch layer of compost or other organic material over the roots of shrubs will usually provide sufficient nutrients for adequate growth and plant health.

A nutrient deficiency can be exhibited by a number of symptoms including stunted growth, smaller than normal leaves, light green to yellowish leaf color and early leaf drop. Be aware that these same symptoms can be caused by other problems such as heavily compacted soil; stresses from insects, disease organisms and weeds; and excessively wet or dry soil. Fertilization will not correct those problems, so be certain that you know the cause of the symptoms and treat them appropriately.

Having your soil tested is one way to determine if applying fertilizer will benefit your shrubs. In the absence of a soil test and other cultural or pest problems, use a complete fertilizer with a ratio of 3:1:2 or 3:1:3, such as 12-4-8 or 15-5-15.

The best time to apply fertilizer is when it will be readily absorbed by the roots of the plant and when the soil is moist, which can be any time from late spring (after new growth emerges) up to early fall. Fertilize after flowering, especially when using a slow-release fertilizer. Avoid fertilizing plants stressed by drought during the summer months. Without water, plants are unable to absorb nutrients, so it is best not to fertilize if water is unavailable.

Since low acidity is of particular importance for rhododendrons, test the soil periodically through your local Clemson Extension office to determine the pH level as well as fertility levels..

Pruning: Rhododendrons need very little pruning. Remove dead or damaged wood at any time. Pruning to shape the plant or to keep it within bounds should be done after flowering.

Deadheading is an important type of pruning. It involves snapping off the dead flower trusses to prevent the development of seeds, which take a great deal of strength from the development of the next year’s flower buds. Break out only the spent blooms to avoid damaging the dormant buds.

Another form of pruning is called disbudding. It involves pinching out the terminal leaf bud on new growth, thus awakening dormant buds and causing side branches to appear. Disbudding is done on new growth and can be done again in the fall. Be careful not to break off a flower bud. Disbudding is a useful technique in shaping plants or making them more compact.