Cultural Requirements of Two Groups of the Heather Family, Rhododendrons and Azaleas
S. D. Coleman, Fort Gaines, Ga.
The Heather family represents a large group of plants, many of which are most beautiful and ornamental. The word heather comes from the Latin or Greek heatherland, "waste land" which is too acid for regular crops used by man. Much of the strong chemical elements of the soil have long since been leached away leaving a humus type soil, composed of leaves, twigs and other vegetable matter, known as organic matter, which usually has an acid content of about pH 5. On this humus soil grow rhododendrons and azaleas.
The word rhododendron comes from the Greek meaning "rose tree." "Rhodo" meaning rose and "dendron," tree; however the plant thus called by the ancient Greeks was the oleander, not the rhododendron. It did not come into cultivation until the eighteenth century. The word Azalea also comes from the Greek, meaning dry and this again seems to be a misnomer. After the larger portion of water has run through the soil drawing in air, much needed for this type of plant, the humus then becomes a water conservative material supplying needed moisture for the plant.
Iron is also needed by this group of plants. It helps chlorophyll formation in the leaves and thus prevents dieback. Chlorophyll is essential to all plants as the foliage is the manufacturing part which changes the different elements into plant food. The lack of iron or chlorophyll is called chlorosis. There are many causes, called fixation or blocked off.
Chlorosis is often caused by an excess of lime, (yellow leaves), if this has not gone too far one may use one table spoonful of ferrous sulphate to one gallon of water and spray the foliage as well as the soil. This should be followed with a sprinkling of flowers of sulphur around the plant to acidify the soil.
Emarginated foliage, (yellow, orange or silver on edges) could be caused by a virus. This puts extra work on the part of the foliage containing the chlorophyll to make a proper balance for the entire plant. This type of plant does not grow so fast and they are used primarily as shade plants for their unusual foliage beauty.
As alkali neutralizes acid, lime is called poison to the acid type plant. Some inorganic fertilizers containing lime or soda are also toxic to plants of the Heather family. In many fertilizers the base contains what is known as trace elements and these elements added to the major elements of nitrogen, phosphorous and potash are necessary for row type plants, grasses etc., but not for those requiring an acid type soil. Organic fertilizer can have the same formula as inorganic. though some writers do not stress this point. The difference is that acid type plants get their food from organic sources found naturally in the soil. Organic fertilizer should also be used very sparingly as humus and water are the most essential elements. Acid loving plants do well on woods soil preferably oak leaf humus, soil from where rhododendrons and azaleas are growing, (the latter is known as inoculated soil) light pond humus with added peat moss or vermiculite to keep from packing.
Burning of the edges of the foliage is a good sign of some nutrient that the plant does not like, or tolerate. This can also cause falling of leaves, dieback, bud decay, wilted flowers, flowers not opening properly and too many buds. A plant with too many buds is a sign that nature is trying to reproduce seed before the plant dies. This can be observed by anyone who loves plant life. he plant may be planted too deep, water logged, the soil too tight or the roots may have been disturbed. Do not cultivate around these plants. Pull weeds and grass by hand. Hormones are made by diluting certain organic acids. Plants stored in sawdust (pine) which is slightly acid helps stimulate root growth and heal ends that were cut in digging the plant. But it is not a soil conditioner as this material disintegrates fast using up natural nitrogen and other nutrients in the soil competing with the plant. Some say, add ammonium nitrate, quite a problem as who can guess how much nitrogen and other elements have been used. An over dose will surely hurt the plant.
For good growing results and better flowers some type of humus oak leaf is best. I would like to see seaweed used as this is claimed to contain all elements that are necessary for plant life. Where available, pine needles are a good mulch as they let in air. Peat moss and vermiculite are conditioners and not mulches, neither is sawdust. Peat moss and vermiculite should be worked into the soil. They keep the soil friable. If not in a well raised bed or a hillside, it is best to dig holes about the size of a bushel basket, then fill the hole with a mixture of leaf mold humus or prepared soil. Water the plant well once a week until it is established, then mulch well. Watch the plants for the first year, after that it is necessary only during dry spells, but they must be kept mulched at all times. Then leave well enough alone and be happy with an abundance of beautiful flowers.
The native species of azaleas do not have the fibrous root system as do their far east cousins and therefore they should be balled and burlapped. Nursery grown plants are far superior to those collected in the wild. These should be handled as liners, cut back to the ground and planted in shaded beds for several years before planting in a permanent location.
In bringing in the many species and varieties to the Trail for study, as well as making a beauty spot for all to see, I studied the soil and conditions in which these plants were growing and then tried to duplicate the setting so far as possible. The Trail was a natural one, I saw plants growing in many conditions and in all cases the ones growing in humus were the better plants. The humus holding a certain amount of water was the main factor.
I know from observation that some plants will tolerate more chemicals in the soil than others, Azalea arborescens will tolerate more than A. calendulaceum, but this does not signify that they would not be better plants if planted right and given ample space to develop into beautiful specimens.