Rhododendron 'Monte Cristo'

Cultivation of Vireya Rhododendrons

Vireya Rhododendrons, like any other plants, have specific cultural requirements if they are to flourish and give pleasure to the grower. Fortunately, their demands are relatively modest and providing these basic needs are met they will provide enjoyment for many years. General guidance notes are given for each of the categories listed below but local growing conditions should also be taken into account. It is worth bearing in mind that the aim is to re-create, as far as possible, the environment experienced by the plants in their natural habitat.


Growing Medium

In the wild, the majority of vireyas are found growing either as epiphytes, clinging to branches and trunks high in the tree canopy, with only small deposits of moss and humus covering their roots; or terrestrially, often in crevices on steep cuttings. Both of these aspects provide excellent drainage after the frequent downpours prevalent in these habitats and this is undoubtedly the most important consideration when growing plants in cultivation.

There are many "recipes" used by growers today but a suggested growing medium that is suitable for a wide range of vireyas can be made up from equal parts of coarse peat, fine grade bark and pumice. This will produce a compost of open consistency that will hold sufficient water to meet the plants immediate needs but without risk of water-logging and at the same time allow air to circulate around the roots. Other ingredients can be substituted where appropriate, including perlite, tree-fern fibre or bracken, coarse river sand or grit (a type suitable for ericaceous plants) or leaf mould. Ideally, the mix should be slightly acidic at around pH5.5 and magnesian limestone can be added if required to lower the pH level.


Vireyas growing in their natural environment receive rain almost daily although most of this drains rapidly away and little is held in the small amount of compost in which the plant is rooted. In cultivation, plants should be thoroughly watered, preferably with rainwater, and then the compost allowed to become barely moist to the touch before watering again. During the cooler winter period when plants are less active the compost should be kept somewhat drier.

The weight of a potted plant is often, with experience, a good guide as to whether or not water is needed however, if unsure, it is better to withhold water rather than risk water-logging which could lead to root rot and the subsequent demise of the plant. If a plant becomes too dry the surface of the leaves may turn dull. In this case, the foliage should be misted and the plant kept in humid, shady conditions and watered only sparingly until there are signs of recovery. Do not soak the compost as the roots will already be damaged from drying out and excess moisture will cause them to rot, thereby killing the plant.


Vireya growers have implemented many different feeding regimes over the years using a wide variety of fertilizers and whilst there have been varying degrees of success, there are several points upon which nearly all agree. Regular light applications of fertilizer are most beneficial, rather than high dosage fast-acting feeds, and it has also been noted that vireyas respond well to regular foliar feeding.

Care must be taken not to overfeed as this can cause unsightly leaf-tip burn and also damage the root system of a plant. If there is a build-up of salts in the compost from heavy feeding, the pot should be thoroughly soaked so the salts can leach away.

Proprietary acid plant foods should be avoided, growers instead ideally using a fertilizer that is high in nitrogen, calcium and magnesium but with low potash, potassium and phosphorus levels.

Pinching & Pruning

'Pinching' refers to the practice of removing the growing tip of a branch to encourage the formation of two or more new growth breaks from that point. If carried out regularly, particularly when a plant is young, it can lead to a more densely branched and compact bush. Whilst pinching may delay the onset of flowering, the numbers of blooms produced will be increased as there will be more branches on which buds can form. Feeding the plant at the time of pinching out the emerging growth usually helps the plant to produce more new shoots.

Some vireyas can be rather "leggy" in habit but most plants will eventually fill out from lower down a bare stem given time and space to develop. Pruning should be undertaken with some caution and if severe should be carried out over a period, allowing the plant time to recover. Feeding beforehand is often worthwhile to ensure the bush is growing strongly and afterwards the compost should be kept slightly drier than usual until new growth emerges.

Temperature & Humidity

When grown in a temperate climate, vireyas will not generally stand freezing temperatures although if exposed to only a short, light frost there may be some re-growth from the base of the plant. Lowland species and their hybrid progeny ideally prefer a minimum night temperature of 15° Celcius (59° Fahrenheit) although most will cope with less. If a plants leaves turn red in the winter months it is often a sign of stress due to the temperature being too low.

Species from the cool montane forest regions are the least demanding and will thrive with a minimum night temperature of 8° Celcius (46° F). Again, two or three degrees lower during the winter will not adversely affect the health of a plant, particularly if reasonable daytime temperatures are achieved, although an extended cold spell may cause it to become practically dormant until the arrival of warmer spring weather.

On the whole, varieties with larger, shiny leaves are more heat tolerant than the small-leaved, higher altitude species that find it hard to cope with high summer temperatures, making them difficult to grow in many areas.

As far as possible, temperatures should be kept below 27° Celcius (81° F) to avoid stress, although given high humidity vireyas readily cope with higher temperatures and at such times regular spraying is most beneficial, at the same time ensuring there is good air circulation around the plants.

Light & Shade

In their natural habitat in the tropics, vireyas experience equal 12 hour periods of day and night with very little seasonal variation throughout the year. Such consistently high light levels are certainly not a feature of the temperate climate in which many vireya growers live, with extended periods of low light during the winter months increasing rapidly at the onset of spring. In these conditions it is sometimes necessary to provide temporary shading on particularly warm, bright days to give the plants an opportunity to acclimatise.

It is generally considered good practice to position plants where they will receive full sun in the morning but be given the protection of dappled shade to avoid the full intensity of the afternoon sun, especially during the summer months when it is possible the leaves may be scorched. Conversely, too little light can have an adverse effect on the production of flower buds. Botanic institutions often use full-spectrum high intensity discharge lights suspended above plants in glasshouses to supplement the amount of light they recieve during winter and similar, smaller models are now available for use by the enthusiast that may prove beneficial in certain circumstances.

Pests & Diseases

Vireyas, in common with other rhododendrons, are generally pest and disease free providing their day-to-day needs are met. Mildew can be a problem when temperatures are high and should be dealt with quickly by spraying with fungicide. If possible, the growing environment should be adapted to ensure there is good air movement around the plants. Small orange spots of rust can occur on the underside of foliage and infected leaves should be removed to avoid spread. Mealy bug, scale, aphids and thrips have all been known to attack vireyas but a healthy plant should withstand their attentions. If the outbreak is severe, spraying with an appropriate insecticide should bring control.

Occasionally a plant may collapse for no apparent reason and this can most often be attributed to either the presence of vine weevil larvae in the compost, seen as small white grubs that feed on the roots of the plant and eventually prevent it from taking up water and nutrients; or alternatively may be due to an outbreak of Phytophthera, a type of fungus that attacks the root system - the first visible symptom being wilting foliage that does not respond to watering. This problem is more prevalent in high temperatures and by the time it is evident, it is too late to save the plant.

Beds, Pots & Baskets

Local conditions will to a large extent dictate the way plants are grown - frost-free areas allowing outdoor display beds, whilst for many growers pot culture is the only practical method. Fortunately, a restricted root run does not present any difficulty for vireyas as they are often found in the wild growing with only a shallow covering of soil, perhaps in a rock crevice or a fork in the branches of a tree.

Whichever method is adopted, excellent drainage is of paramount importance (see 'Growing Medium') and when planting in a raised bed the plant should be placed on the surface or in a shallow hole and the compost drawn up just sufficiently to cover the root ball. It is essential to ensure that the plant is positioned no deeper than it was in its container as this invariably proves fatal. This applies equally when re-potting.

Growing in pots has the advantage of portability however vireyas should not be over-potted as there is a danger of the compost turning sour, with a consequent detrimental effect on the health of the plant, whereas under-potting carries few risks. With regard to the type of container to use, plants in clay pots may need watering more frequently than those in plastic pots however are less likely to be over-watered. Taller specimens are perhaps better suited to clay pots, benefiting from the extra stability provided by the weight of the pot. Whatever is chosen, ample provision should be made for drainage.

Hanging baskets are particularly good for displaying those vireyas with a more sprawling or pendulous habit as the branches can be encouraged to hang down, echoing their epiphytic tendencies. A wire basket lined with moss and filled with a suitable potting mix is also a most attractive way of presenting many of the miniature varieties.