Culture Notes on Vireya Rhododendrons
Dick Cavender
Sherwood, Oregon
Vireya rhododendrons have a history extending back to the early 1800s. They were among the first rhododendrons introduced to European conservatories and greenhouses and were very popular until World War I. Their recent history has been marked by frustration and ignorance. Vireyas have a reputation of being tender, finicky, and generally hard to grow. They are not. They do have some specific requirements, but then so do most other plants. They will stand a great deal of neglect and drought if the soil and temperature are to their liking. Vireyas bloom at all times of the year, some more than once and a few almost constantly. Many are fragrant and a few extremely so. If you can grow a cymbidium orchid or a Boston fern, you should not have trouble growing vireya rhododendrons.
Soil . In nature, most vireyas grow as epiphytes or in areas of extremely sharp drainage. We must duplicate these conditions in our homes. Roots must have a loose, airy, very acid medium. We grow most varieties in a mix of equal parts of peat, fine fir bark, course bark chunks and pumice. Perlite may be substituted for pumice and pine bark, and chopped pine needles or other coarse material may be substituted for fir bark.
Water . The soil should be allowed to get slightly dry on the surface and the pot feel light before watering. This must be done with care so as not to let the plant wilt. When watering, soak the pot well and then let it drain. This will also help prevent fertilizer salt build up.
Fertilizer . Vireyas are very sensitive to over fertilizing. It is best to apply too little rather than too much. Fish fertilizer strength is adequate. Once a month is fine. If you want vigorous growth, fertilizing every other watering will produce it, but you must leech the pot well between each application. Brown around the leaf edges indicates over fertilizing. A happy plant will have good green leaves and hold three or four or more sets of leaves. An unhappy plant will have only one or two sets of yellowish leaves.
Light . Full sun in the morning or filtered sun all day is best. Give as much light as possible short of scorching. The plants will sun burn easily because they are in small pots and short on water. Outdoors in summer under the high filtered shade of a large tree is great. Indoors in an east or north window is best.
Temperature . Vireyas are tropical; temperatures into the 90's with high humidity is fine but not desert dryness and direct sun. In general they will grow well from the low 60's up. A safe minimum holding temperature is 40F. Container plants should not be allowed to freeze. Plants planted in outdoor beds in USDA Zone 9 or 10 will tolerate an occasional light frost with minimal damage and may be frozen to the ground every few years. Generally, as long as the roots are not frozen and the cold snap not prolonged, vireyas will come back from the roots. They may even be better for the severe pruning, producing a nice bushy new growth. If planted outdoors, they require the same well drained, acid soil as used in containers. I would also suggest planting in the most frost protected spot in the garden.
Humidity . Higher humidity is desirable. A spa or hot tub area is a great spot. A solarium or window greenhouse is good. It is not necessary to mist plants, but a shallow pan filled with gravel and water under the pot will help temper the dry air found in most homes. They will appreciate a vacation out of doors while there is no danger of frost.
Pruning . Not only can rhododendrons be pruned but they require it. Vireyas are no exception. They should have the new tip pinched out when young to form a good branching habit. Older plants can be pruned after bloom or when the growth has hardened for cuttings. The problem with pruning is that it delays blooming and so a compromise may be a few judicious whacks when young, allowing the plant to get a bit leggy and blooming, and then a hard pruning back. Just don't cut off all the leaves.
Encouraging Bloom . Since vireyas are from equatorial regions, they bloom anytime of the year. In Oregon, bud set is heaviest in late summer with most bloom in fall and winter. Plenty of light is a must. Each flower bud has several pushes of growth behind it so avoid over pruning. Dry household air may interfere with bud opening. If so, a plastic bag can be placed over the plant for a few days when buds are about to open. That pan of gravel and water also helps with this problem.
Containers . I tend to under pot for lack of time more than any other reason. Vireyas do not mind being root bound and may prefer it. Under potting lessens the problem of over watering. A 6- or 8-inch plant of one of the small leafed varieties will be fine in a 4-inch pot. A 2- to 3-foot plant of one of the large leafed varieties will do great in a 2-gallon pot. If the plant gets top heavy, add some large rocks or a brick to the bottom of the pot. I have an extreme example of under potting: a 3-foot high plant of Rhododendron laetum in a 4-inch pot. This plant blooms several times a year and is at least five years old.
Problems . Spindly growth = poor light. No bloom = poor light, too much water, over pruning. Leaf drop = cold, compacted over moist soil, lack of fertilizer. Wilting = lack of water, root rot from being kept too wet. Brown leaf edges = over fertilizing, excessive drying, sun burn. Arrested flower opening = dry atmosphere.
Propagation . Vireya cuttings root readily. When the growth has matured, a 2- to 3-inch cutting, dipped in light rooting hormone, and stuck in peat/perlite will root in three to five weeks. Several cuttings placed in a 6-inch pot, watered in, and enclosed in a plastic bag can be rooted in a bright, warm (70°F) window. If you have rooted other rhodies or azaleas you will have no trouble with vireyas. Vireya seed has very short viability and is very slow. It may take a year or more to produce a 1-inch plant.
E. White Smith, a member of the Tacoma Chapter, edits the Vireya Vine, a newsletter with contributions by vireya growers.