The Basics as simply as 1, 2, 3…
1. Rhododendrons must have a constant supply of moisture. You may occasionally see a rhododendron that will survive without being watered, but it does so only under protest.
2. Rhododendrons must never sit in stagnant water. Roots submerged in poorly oxygenated water will likely die, though a plant may survive through better drained surface roots..
3. Rhododendrons must be grown in an acid medium (pH 5-6) that is coarse enough for the roots to have access to needed oxygen.
Understand and provide these three conditions and you will succeed wherever you live. These requirements aren’t difficult to provide once you understand rhododendrons’ needs relative to your specific soil and climatic conditions.
So, you ask ?
“How can I provide these 3 basic needs?”
Consider the growing medium and include in your thinking the soil and drainage that is underneath the proposed planting. You must determine whether or not your soil has good drainage. If heavy clay is present you must overcome this barrier. Dig a small hole and run some water into it; if the water does not disappear in a very few minutes, you have poor drainage. This is not a sure test, but it will give you a good indication. Now, examine the soil texture: Is it sandy, or is it composed of fine clay particles? Sometimes the topmost soil layer will drain well, but there will be hardpan underneath it that will not drain. So, watch for this condition.
Where can I plant ?
Site, Soil, Planting guidelines….
Rhododendrons prefer a site that provides afternoon shade, some protection from wind, good drainage and air circulation. Sloping terrain is also a decided advantage.
Well-drained soil is a must. Use raised beds to plant on top of poorly drained soils. Ideally, soil should be acid (ph 4.5 – 6.0) and high in organic matter. Pine bark, coarse sphagnum peat moss, composted wood chips and other such materials can be worked into the soil to improve organic matter content and soil drainage.
Container plant root balls must be sufficiently disturbed so that roots extend out from the ball. The planting hole should be wide but shallow. Loosen and amend soil only 20 – 25cm deep so that the root ball sits on solid ground to prevent sinking. Plant only as deep as the top of the root ball with no soil on top of the ball. Do not pack soil tightly around the plant as tender roots will be destroyed. Mulch 10cm deep and water thoroughly.
If plants hold good green color and grow well, no fertilizer is needed. Rhododendrons are not heavy “feeders”. A soil test can determine what elements are deficient if plants do not perform well. When necessary, apply a fertilizer formulated for acid loving plants in late Winter or early Spring. Don’t fertilise after Dec 1st.
How do I look after my Rhodo ?
Mulching, Watering, Pruning….
Mulch with 10cm of pine bark, pine needles, oak leaves, composted wood chips or other loose airy material. Do not use leaves, grass clippings or other materials that pack down.Keep mulch away from plant’s stem.
Proper watering is an important after care practice, especially for the first several years as plants become established. Keep the soil moist but not wet. Water deeply, in the absence of equivalent rainfall. Don’t water again until the soil starts to dry out. Afternoon wilting of new growth is normal. If leaves become turgid a few hours after sundown, no additional water is needed. Water requirements diminish in late summer and early autumn as new growth hardens up for winter. Plants should, however, be watered going into winter following a dry autumn.
Deadheading the spent flowers on a rhododendron tends to focus the energy of the plant towards new flower production and general plant health. It also improves the sight of the plant when not in bloom.To deadhead, use your fingers and gently rock the base of the spent flower truss back and forth until it separates from the plant. That’s it. Now you can either toss the spent bloom under the shrub for mulch or discard on the compost heap.
Problems most often encountered?
Root rot – leaves wilt on the entire plant and do not respond to watering – caused by poorly drained soils – plants so affected cannot be saved.
Lace bugs – tops of leaves turn gray – spray with neem oil , or use a systemic insecticide like confidor, you can also use confidor tablets.
Borers – first noticed by a wilting twig or sawdust beneath the stem – cut off the affected branch below borer damage or crush the borer larva by inserting a wire.
Weevils – first signs are leaves becoming irregularly notched around the edges – spray with a systemic insecticide – Confidor and use Confidor tablets
Die-back – all leaves on a branch wilt and eventually fall off – cut the affected branch back to healthy wood
These guidelines apply particularly to elepidote (large-leaf) rhododendron. Generally speaking, cultural requirements are less “demanding” for lepidote (small-leaf) rhododendron and azaleas, both evergreen and deciduous. They tolerate, and to some extent require, more sun than elepidotes, and azaleas will also tolerate less well-drained soil. In all other respects, the general guidelines outlined above apply to all plants in this family.