Rhododendrons require very well drained soil. Standing water replaces necessary oxygen at the root zone, often resulting in a stunted or dead plant.
If the soil is too heavy, or alkaline, plant in raised beds with a mixture of topsoil and ground bark.
It is best to plant where there is filtered sunlight though some varieties will flourish in full sun. Avoid sites with reflections of light-colored houses and paved areas.
Do not plant in very windy locations like the corner of a house. Consider that some air movement is necessary to reduce excessive dampness and potential for fungus diseases.
Avoid sites under roof overhangs, adjacent concrete foundations and under trees with dense shading or aggressive root systems.
In colder areas it is a good idea not to locate rhododendrons with an Eastern exposure where the foliage is subject to quick thawing by the rising winter sun.
How to Plant
Provided the soil is moist and workable, rhododendrons can be planted at any time of the year. Planting on hot days should be avoided as newly transplanted plants may not have the root system to take up sufficient water.
Balled and burlapped plants often will be a bit dry and should be moistened by soaking in a tub of water at least 5 minutes prior to planting.
Natural burlap can be peeled back from the top third of the root ball, synthetic ties or wrapping should be removed completely.
Container-grown plants should also be soaked. Root bound plants should have their root balls cut and disturbed before planting.
Dig a hole wider and deeper than the root ball. The size of the hole will depend on the soil condition:
In heavy clay or alkaline soils plant so that the crown of the rootball is a few inches above the soil level. This allows for greater aeration at the root zone. In extremely heavy soils rhododendrons should be planted in a raised bed of a well drained soil.
In moderate clay or sandy soils prepare the hole twice the diameter, and again as deep, as the root ball. Mix the backfill soil with at least 50% organic material such as shredded bark, peat moss and compost.
In rich woodsy loam the hole need only be large enough to easily contain the root ball.
Fill in the soil and water sufficiently to settle. The top of the root ball should be level, if not slightly higher than the surrounding soil.
Sprinkle a small handful of Rhododendron-Azalea-Camellia fertilizer around the drip line- not near the trunk.
Mulch with pine needles or bark chips to hold in moisture, cool the soil surface and control weeds. Take care to keep it away from the trunk.
FERTILIZER: Younger rhododendrons should be fertilized just before and again after blooming. Broadcast a light handful of standard rhododendron fertilizer around the plant away from the trunk and as far out as the spread of the foliage (drip line). Older, well established plants do not need to be fertilized unless the foliage color indicates a deficiency, or the plant is not flowering satisfactorily. If the soil is above a pH of 6 then an iron chelate may be useful in maintaining a good green plant color. If soil and water is very alkaline, sulfur applications will be necessary once or twice a year. Please consult with experts in your area.
WATER: The roots should be moist but never too wet for a long period of time. Once a week watering equivalent to about one inch should be satisfactory. Rhododendrons may benefit from extra water while they are blooming and until the new growth has hardened off. New plantings should receive supplemental water until established. We have found rhododendrons appreciate overhead watering during very hot periods.
PRUNING: Pruning is seldom needed if the plants have been selected to fit comfortably in their location. Spring is the best time, immediately after flowering. The cut should be made just above of whorl of leaves. The leggy branches of older plantings may be cut back to a more desirable height. This more severe pruning will force lower dormant growth buds to emerge. Pinching as they start in the spring will encourage branching and produce a more compact plant.
DEADHEADING: Breaking off faded bloom clusters will provide your plant with the stimulus for stronger new growth. Care should be taken not to damage the growth buds about to break immediately under the faded flower.
PEST CONTROL: Rhododendrons are relatively pest free. Root weevils and lace bugs are pests that require the most attention.
Rooted Cutting and Liner Care
All Van Veen Nursery rhododendrons are cutting-grown and guaranteed to be true to name. Under Kathy's close supervision, cuttings are gathered and prepared between July and November. They are planted in open benches in traditional glass greenhouses and supplied with bottom heat and high humidity.
Since root development is the all-important consideration, most plants sold as rooted cuttings have no top growth. However, they do have large, vigorous rootballs.
PLANTING: Pot up or plant in a protected area. Use a loose, well draining medium such as one containing some bark, compost, or perlite.
WATERING: Keep soil thoroughly wet but never soggy.
PROTECTION: Shelter from heat, frost, and wind for the first 6-12 months in a protected area such as a plastic covered hoop house. Keep it open and shaded in summer. Antidessicants such as Vaporgard can be used as protection from both heat and cold. Also, antidessicants may help in preventing some fungal problems.
SHAPING: New growth is expected in 1-2 flushes the first summer. Pinching out the center bud will help the lateral buds develop thus producing a more bushy plant.
FERTILIZING: Use a liquid fertilizer 20-20-20 1T/gal. applied once every 7 to 10 days between April and August. Stop fertilizing in time to allow new growth to harden before first frost. Epsom salts, 1 T/gal., can be applied occasionally to add magnesium for better color.
WEEDING: Hand weeding is best because plants are shallow rooted. Preemergent herbicides are not recommended for these young plants.
DISEASE CONTROL: Root rot occurs in some varieties, especially in yellow flowered rhododendrons, when conditions are both hot and wet. In the Pacific Northwest this is in July and August. Well drained planting soil is essential. New biological products such as Rootshield or Actino-iron contain beneficial organisms that form protective colonies on the plant roots. These must be applied before problems are expected. Powdery mildew may be evident in some varieties and some climates. Use a systemic fungicide, such as one used for roses, so there is no need to spray leaf undersides.
PEST CONTROL: Weevils may be a problem. Watch for notching from the chewing beetles in the summer. Various insecticides may be used to control them. The grub stages of the weevil, which exists in the soil in fall, winter, and spring, does the most damage. It eats roots and underground stems and may completely girdle the plant and kill it.