Rhododendrons, especially the evergreen kind, prefer crumbly, peaty, humus-rich and sharply drained soil. They are “surface rooters” with compact and dense roots, so the fertile layer of soil does not have to be very deep. As for mineral soils, rhododendrons prefer sandy and well-drained soils, since they are acid. Sandy and other mineral humus-poor soils can be improved by addition of organic matter – peat moss, tree leaves (oak), pine or larch needles, bark, well-rotted grass clippings. The planting hole for the rhododendron is usually made 3 to 4 times larger that the root ball, then it is backfilled with the prepared planting mixture. In the following years, the plants should be mulched annually. Rhododendrons are not amenable to clay soils, since they are heavy, poorly drained, prone to compaction and impermeable to water and air. Of course, they could be drained and amended with organic matter, but rhododendrons grown on such soil will still need a lot of maintenance.

In Asia, where many rhododendron species grow in the wild, most precipitation occurs between May to October. During this period the rhododendrons flower and produce new growth actively. In our country this period is much drier, so it is of utmost importance that both young and adult plants get sufficient moisture. Mature plants are less vulnerable to drought, but even they can suffer irreparable damage, should their leaves stay limp for an extended period of time.

Newly planted rhododendrons should be watered regularly to prevent them loosing moisture. Deciduous rhododendrons are more susceptible to drought damage than their evergreen relatives. The plants need most water during their flowering, the flush of active growth and the flower bud setting, all of which fall in a period between May and July. If short of moisture, the flowering of rhododendrons will be very brief. Plants should be watered early in the morning or late in the evening, when he sun is less bright, since sunlight can scorch the leaves of evergreen rhododendrons, which will show in appearance of numerous brown spots. In order to retain moisture within the soil, plants should be mulched.

The evergreen rhododendrons are not vulnerable to winter freeze,

 but they tend to get desiccated by cold. The evergreen leaves of these plants continue evaporating water in winter. Their roots cannot access water, the ground being frozen. Therefore, evergreen rhododendrons should be watered amply in late autumn, before the ground starts freezing over. The plants are adapted to fight the winter desiccation - when temperatures drop below zero, their leaves go limp and roll up at the edges, so as to conserve moisture. After an extended cold and dry winter, rhododendrons can remain limp even after the snow is gone in spring, which means that plants are in need of watering, having lost a lot of moisture. A good drench on the crown is helpful, since this way water is absorbed faster. Normally, a couple of weeks of generous watering are enough. Leaves of evergreen rhododendrons are a good indicator, which shows the moisture levels of the soil.

The rhododendrons love moist soil, but not the waterlogging. Soil needs to be permeable to water and air, so make sure there is a layer of well-draining material on the bottom of the planting hole. When plant grows on a waterlogged site, it looks just like the one which has lost too much moisture: its leaves go limp, roll at the edges and turn brown, which eventually results in demise of the plant.

© Mygarden.lt, 2009

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