Roanoke Times
Copyright (c) 1995, Landmark Communications, Inc.
DATE: THURSDAY, June 3, 1993 TAG: 9306030026
SECTION: CURRENT PAGE: NRV-9 EDITION: NEW RIVER VALLEY
SOURCE: Joe Hunnings
DATELINE: LENGTH: Long
The fact that they require little care once they are properly established also contributes to their predominance in our landscapes.
To help you maintain your azalea and rhododendron plantings for optimum enjoyment, I have put together a few tips:
Fertilization: Avoid using general garden fertilizers for rhododendrons and azaleas.
Use fertilizers specially formulated for acid-loving plants. Be sure to follow the directions carefully.
Fertilizers supplying ammonium nitrogen are best.
Rhododendrons and azaleas grow well naturally at relatively low nutrient levels. Therefore, fertilization should be done carefully or the fine, delicate roots close to the soil surface will be damaged.
A fertilizer analysis similar to 6-10-4 applied at 2 pounds per 100 square feet to the soil surface is usually adequate.
Cottonseed meal is also a good fertilizer.
Fertilizing should be done right away.
Don't fertilize after July 1. Late-summer fertilization may force out tender fall growth that will be killed by the winter.
Acidity: Soil acidity must be maintained to insure good growth.
If the soil pH is above 6.0, apply iron sulfate or agricultural sulfur to the surface.
The amount to apply will depend on the existing pH, so you must have an up-to-date soil test. Soil testing can be done through our cooperative extension office.
Mulch: The thickness of the mulch must be maintained but should not be excessive. As the old mulch decomposes, add new mulch.
Mulch should be moved away from direct contact with stems in early fall to allow hardening during the onset of cold weather.
Replace and replenish mulch before a hard freeze.
Weed Control: Mulches are your best defense against weeds.
However, if weeds become a problems and physically removing them is not an option, several herbicides are registered for use in weed control around azaleas in the home landscape.
Always be sure to read the label for correct application rates and times and to see if any cultivars are listed as ones that may be damaged.
Consult publication 456-004, "Pest Management Guide for Home Ornamental Plants" for a list of appropriate herbicides.
Watering: Many rhododendrons and azaleas have been killed by overwatering in sites where drainage was faulty.
If water does not drain away readily, drain tiles should be installed or a raised bed built.
Avoid excessive irrigation in fall. Plants kept dry in September will tend to harden off and be better prepared for the winter.
If the fall has been excessively dry, watering should be done after the first killing frost. At that time, watering will not reduce winter hardiness but will prepare the plant for winter.
The soil should be thoroughly moist before cold weather sets in. The best time for fall watering is about Thanksgiving.
During the growing season, be sure that at least one inch of water (from rain or irrigation) is available per week.
Pruning: There is little need for pruning azaleas and rhododendrons. If growth becomes excessive, reduce the size of light pruning.
It is important to remove the flower stems on rhododendrons as soon as flowering is complete, although this practice is not necessary on most azaleas. Failure to do this will reduce flowering the following year.
Break out only the dead flower cluster, not the young buds clustered at its base.
Azaleas sometimes branch poorly and form a loose, open shrub.
The plants' form can be improved by pinching out the soft, new shoots of vigorous growing plants.
Do not pinch after July because flower buds will not have time to develop for the following year.
Winter protection: The two winter enemies of evergreen rhododendron and azaleas are wind and sun. Most damage shows up as split bark, dried leaves, or dead or damaged flower buds.
If hardy types are selected and proper locations are chosen, little or no winter protection is needed. If existing varieties show winter damage, provide some protection.
Don't be alarmed when leaves curl and droop on cold days; that is normal.
Sunscald and scorch: Large-leafed evergreen rhododendrons are sometimes subject to sunscald during winter. This is most likely to happen if the plant did not receive ample moisture before freezing in fall.
The exposed portions of the leaf (usually the central portion when the leaf was curled) may become brown.
This browning may also appear on the edges of some leaves.
To prevent scorch, plants should be well watered in the fall if rainfall has been sparse, protected from drying winds, mulched well and given some shade.
Iron chlorosis: If leaves turn yellow in the sections between the veins, but the veins remain green, iron deficiency is the cause.
Chlorosis may also result from soil that is not acid enough, poor drainage, nematodes or other conditions that cause root or stem injury.
Iron chlorosis can usually be temporarily controlled by spraying the foliage with an iron (ferrous) solution or with chelated iron.
Insects and diseases: There are several insects and diseases in Virginia that commonly bother azaleas and, to a lesser extent, rhododendrons.
The most common insect problem is the azalea lacebug, but also troublesome can be aphids, leaf miners and tier, and scale.
Azalea lacebugs are small insects with a delicate lace-like texture that feed on the undersides of azalea leaves.
Their feeding causes the upper surface of the leaf to look spotted and may eventually turn the leaf gray or brown.
The most common diseases on azaleas are Phytophthora root and crown rot and Ovulinia petal blight.
Rhododendrons can also be bothered by Botryosphaeria canker and dieback.
Consult extension publication 456-018, "Pest Management Guide for Home Grounds and Animals" for a list of control measure for insects and diseases.
Joe Hunnings is the Virginia Cooperative Extension Service agent for agriculture in Christiansburg. If you have questions call the Montgomery County extension office at 382-5790.
by CNB