Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F · Comment About Planting
Rhododendrons prefer growing in well-drained but moist, humusy, acidic soils. I always plant them on slight to steep slopes or on raised mounds to provide good drainage. When planting in heavy clay soil it's a good idea to add in some organic compost to loosen the soil and also to help retain some moisture. Regarding sun exposure, rhododendrons like morning sun with afternoon shade to dappled or filtered all day light. In the Deep South, direct afternoon sun is not good for most varieties and will often scorch the foliage.

When planting a container-grown rhododendron (remember to plant on sloped ground for best performance), dig a hole three times the width and no deeper than the container the plant was grown in. If the soil is heavy clay thoroughly mix in organic matter or compost at a 50/50 ratio with the native soil removed from the planting hole. Set the plant in the planting hole making sure the top edge of the root ball is even with or slightly above ground level to allow for settling.

If you are planting on level ground, leave about half of the root ball above the ground and use your backfill mixture, and additional soil if necessary, to create a mound that starts at the top edge of root ball and tapers gradually to grade/ground level. This mound should extend to a foot or so beyond the perimeter of the planting hole you dug.

After planting water thoroughly to drench soil and then apply a 1.5 to 2-inch layer of organic compost, shredded wood mulch or pine straw. During the first summer,water as necessary to keep soil moist but not consistently wet. When established, you can reduce the amount of supplemental irrigation during the summer months, only watering during prolonged dry spells or when you see new growth drooping due to dry soil.

Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F · Comment About Pruning
Typically, rhododendrons, especially the dwarf varieties, do not require much pruning except to remove spent flower clusters, also called "trusses," or damaged or dead branches. You can, however, prune rhododendrons to control shape or size or to rejuvenate old plants that have become spindly.

Maintenance pruning involves pruning spent flower clusters and removing damaged, diseased or dead branches. Remove pent flower trusses as soon as they've finished blooming by simply using a pair of sharp hand pruners to cut off the truss about 1/2 inch above the emerging new growth. When removing diseased branches, make your cut below the damaged portion of the plant, taking care to cut into healthy wood right above a dormant bud. To avoid spreading disease, make sure to disinfect the pruners between each cut you make with rubbing alcohol or 3% hydrogen peroxide.

Pruning to shape and to encourage denser branching, or to control plant width or height, can be done in early spring when the plant is still dormant or after flowering for plants that have flower buds. To shape a rhododendron, follow the branch from the tip down to the last whorl of leaves you want to keep. (Do not make your cut below the last cluster of leaves on a branch). Make your pruning cut about 1/4 inch above the topmost leaf in the cluster. Repeat as needed throughout the shrub. Shaping should not be done on old, leggy, large rhododendrons as their open habit requires a more drastic technique called rejuvenation pruning.

Rejuvenation pruning is best done in late winter or early spring, before new growth has begun to emerge. This type of pruning involves either cutting the entire plant back to 6 inch stumps or cutting or 1/3 of the branches back to 6 to 20 inches in height over the course of 3 years until the entire plant has been pruned. Know that there are risks when cutting the entire plant back to 6 inch stumps. Diseased or weakened plants might not be able to handle the shock well enough to produce new growth and die in trying to do so. There is less risk of death when removing 1/3 per year, and I like this method best.

Before pruning to rejuvenate a rhododendron look along the vertical branches and you should see very small pink buds about the size of a pen point. When you have decided how far you want to cut a branch back, try to make your cut about 1/2 to 3/4 inch above a cluster of these pink buds. The more buds, the more new branches will emerge to form a denser structure to the plant. As previously mentioned, prune about 1/3 of the branches back each year over the course of 3 years.

Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F · Comment About Feeding
I fertilize rhododendrons with an Azalea, Camellia & Rhododendron type fertilizer after the bloom in spring. Alternatively, you can use an organic plant food. Rhododendrons like an acid soil (5 to 6 pH) so it's a good idea to have the pH of your soil tested. If your soil is too alkaline (above 6.5) apply chelated iron, soil sulfur and or aluminum sulfate to lower pH. It's also not a bad idea to mulch every spring with composted organic matter. This helps feed the plants naturally and conserves moisture during the hot summer months.

Gardenality.com · Gardenality Genius · Zone 8A · 10° to 15° F · Comment About Problems
When planted right, and in the right spot, I don't see too many serious pest or disease problems with rhododendrons. Consistently wet or soggy soil can cause root diseases that can lead to death of the plant.