Rhododendrons are one of the most diverse groups of ornamental plants. They include some of the most spectacular flowering shrubs, as well some of the smallest. They are at their height of bloom in late spring and early summer. Some varieties bloom as early as January or February while some bloom as late as August. Most varieties, however, bloom during April, May, and June.
Whether they are grown in large groupings or as individual plants no other shrub gives such a diverse range of colours. The variations in the form, colour, texture, and size of the leaves are so remarkable that even if they did not flower many varieties would still make outstanding specimen shrubs in your garden.
Choosing the Right Location
Rhododendrons need to be planted in an area where there is lots of humus, or good workable soil. They have a very fine shallow root system, so they do not do well in heavy clay or very rocky soils. The shallow roots also mean that they do not like cultivation of the soil at their base. Manure, compost, or peat moss makes for excellent soil conditions for their roots.
One thing that Rhododendrons require is a consistent supply of moisture. Due to the fact that their root system is very shallow the soil should not be allowed to go dry for very long. Conversely, Rhododendrons should not be allowed to sit in stagnant water. Root submerged for a period of time will die. The reason that Rhododendrons are so successful here on the west coast is our warmer wet winters and our cool summers.
Planting Your Rhododendron
When planting Rhododendrons be sure to add compost, or peat moss to the soil as well as some Transplanter (5-15-10) or All Purpose (6-8-6) fertilizer to encourage good root development.
Mulching is a very important part of growing Rhododendrons successfully. The reason for mulching is to keep the roots cool in the summer, protecting them from sudden soil temperature changes in winter, as well as preventing the soil from drying out in the summer. Mulching helps reduce the growth of weeds. One of the best mulches to use is Bark Mulch but you can also use our Garden Soil, or Sea Soil.
For healthy vigorous blooming rhododendrons, they should be fertilized on a regular basis with our Evergro Rhododendron and Azalea Fertilizer (10-8-12). The first application of fertilizer should be made in March or April before they begin to bloom. A second application should be made sometime in June or July after they have finished blooming. This second application is made so that they can develop blooms for the following year.
- Yellow Leaves – If your Rhododendron has pale green or yellow leaves it may be a result of a lack of Nitrogen or Iron in the soil. Fertilizing with the Rhododendron and Azalea Food will help to solve the problem.
- Root Weevils – Weevils are black beetles that live in the soil and climb the Rhododendron at night and eat holes in the leaves. The larvae of the weevils also eat the roots of your Rhododendrons. You can control the weevils by applying beneficial Nematodes to the soil in April and by applying the sticky Tanglefoot to the trunk. If more severe control is required there is the Borer and Weevil Killer spray that can be applied to the trunk.
- Spider Mites – These are microscopic insects that suck on the bottom of the leaves causing the top of the leaf to become spotty and turn a mottled-brown colour. To control these, you can apply a SafersTM product like Insecticidal Soap, Trounce, or End-All.
- Sunburn – If the leaves become light yellow with brownish burned areas on the sunny side of the plant you may have sunburn. If the leaves not in the sun are a deeper green, then sunburn is likely the problem. It is best to provide the plant with more shade or move the plant to a shadier location.
- Windburn – If the edges of the leaves are turning brown then windburn may be the cause. Protect the plant from the wind or move the plant to a more protected area.
- Fertilizer Burn – This shows as brown burn spots on the tips and the edges of the leaves and will be on the entire plant not just the sunny side. Watering the soil heavily to leach out the excess fertilizer will help.
- Chlorosis – This is when the plant has dark green veins with yellow areas between them. This is often caused by a lack of iron. Apply Iron Chelate in a water-soluble form to the leaves and water into the roots. Chlorisis may also be caused by other types of damage to the roots such as root rot, root pruning, root weevils, or root death as a result of too much fertilizer.