Care and Maintenance
Select varieties for resistance to cold and heat, for season of bloom, color of flowers, attractiveness of foliage, and especially for type and ultimate size of the plant for the particular landscape spot in your garden. American Rhododendron Society hardiness ratings will help you with your decision. Plant and flower descriptions, as well as colored photographs, are available for most varieties. Please do not hesitate to ask your local ARS members, County Extension Agents or nurserymen for their expert advice.
Rhododendrons prefer a porous, well-drained acidic soil where there will be some high, broken shade.
In the Pacific Northwest, rhododendrons generally can take more sun than those growing in hotter areas of the country or where there are fewer cloudy days. Generally, rhododendrons with smaller leaves or smaller plant structures can take more sun. Species of these types generally are found in the alpine areas where the sun is more intense, but these plants also receive more moisture in the form of "low" clouds or fog. The smaller plants also require very good drainage.
Avoid planting too close to a house foundation or under a roof overhang where watering might be a problem or under trees which make dense shade or have shallow, aggressive root systems.
Observe the amount of growth that the plant has put on in the last year. Multiply the length of this growth by 10 and you can estimate how large the plant will be in 10 years. Use this as a guide as to where you might want to plant it. Also observe the size of the leaves on the plant, if the leaves are longer than 6 inches, you may want to ensure that the rhododendron is planted in a location that is sheltered from strong winds.
A microclimate is an area where the weather conditions are different than the general conditions for the larger area. If your garden is located in a low spot, it is likely that the temperature will drop lower than the reported temperature for the area as the cold air settles in the depression. If the garden is on a slope, then the cold air will drain down the slope and settle in the lower garden. The location of the garden can also receive either more rain or less rain than the norm because of its location and can be more exposed to the wind or be more sheltered. Proper siting of your garden can take advantage of these differences.
If the rootball seems dry, soak the rootball while you are preparing the hole. If you have a lot of clay in your soil and do not have good drainage or if your soil is alkaline, you may prefer to plant the rhododendron on top of the ground or in a raised bed.
Dig the hole half again as large as the rootball. If the soil does not have good drainage, you may prefer to add a 50% mixture of moist peatmoss to the planting hole.
Before placing the plant in the hole, remove the burlap wrap or plastic container. If the plant is rootbound (a lot of exposed roots), work the roots loose so that they can grow into the new planting area. Otherwise, gently, but firmly loosen the rootball with your hands to encourage new root growth. DO NOT ALLOW THE ROOTS TO DRY OUT IN THE BREEZE OR TO BECOME EXPOSED TO THE SUN.
Put some of the soil mix into the bottom of the hole and place the rootball into the hole ensuring that the top of the rootball is no lower than the surrounding ground. Also, leave the top of the rootball uncovered by backfill. Water well.
After planting, mulch with bark, wood chips, pine needles or any coarse organic material to conserve moisture, keep the soil cool and restrict the growth of weeds. DO NOT mulch with peatmoss because when the peatmoss is dry, water will run off of the area and will not penetrate the peatmoss to get to the rootball.
Try to avoid placing the mulch against the main stem
Fertilizing should be done with discretion. After the plant becomes established, fertilizing should be done lightly or only if the plant is showing signs of needing fertilizer.
Soils vary across the Country and certain fertilizers are made for specific areas. Unless your soil is quite acidic, pH 6 or below, use a mixture containing nitrogen such as ammonium sulfate - often called "Rhododendron, Azalea or Camellia Fertilizer". Always thoroughly water plants at the time of fertilizer application. At planting, scatter a small amount on top of the soil before mulching. Later applications should be on top of the mulch and watered in. Applications may be made in the early Spring if the plant appears to need fertilizer.
Where soils are more alkaline, above pH6, an iron chelate may be useful in maintaining a good green plant color. If the soil is very alkaline, sulfur applications may be necessary. DO NOT USE aluminum sulfate. Please consult your local nursery or County Extension Agent.
"Deadheading", or breaking off faded flower clusters, tends to encourage flower buds for the next blooming season and will prevent the plant from using its energy to develop seeds. Also, it makes the plant look more attractive.
Care should be taken not to damage the new growth buds that may be starting to expand immediately under the faded flower.
Pruning is seldom, if ever, needed if the rhododendron has been sited to fit comfortably into the landscape. But, if it is done, it should be done by mid Spring so the new growth will be completed and "hardened off" before mid Fall.
Occasionally, pruning may be necessary to remove dead or damaged stems in which case, the stem should be cut back to the prior stem or until live wood is found. This will provide a stimulus for new growth .
If the plant is getting too leggy, shaping may be done in the Spring immediately after blooming. Pruning should be done approximately one inch above the dormant buds. Also, you may consider moving the plant to a location where it can receive more light.
To encourage branching in young, upright plants, break out the single terminal shoot just as growth starts to push in the Spring.
Rhododendrons are relatively free of pest problems; but in some areas, certain insects and plant diseases may need to be controlled. Because of local conditions, and the restrictions on chemical pesticides, ask your certified nurseryman or consult your local County Extension Agent.
Certain varieties of rhododendrons are more susceptible to pests or diseases. Therefore, your best option may be to destroy the plant and get another variety.