Energy Conservation In Rooting Deciduous Azaleas
Elizabeth K. Cummins, Marlboro, New Jersey
Reprinted from the Plant Propagator, Vol. 28, Number 2, June 1982.
For about ten years I had been propagating deciduous azaleas before anyone told me they were difficult to root! Yes, they are difficult, but as with all plants, they can be rooted and grown on successfully if a few basic rules are followed.
Correct timing is the main consideration. All deciduous azalea cuttings should be taken from the current year's growth, while still in a green condition. In the New Jersey area this would normally occur between late May and mid-June. A four to six inch cutting, made from a healthy, well fertilized plant, taken at that time should root in a greenhouse, under mist, in six to eight weeks. They can be rooted from green cuttings in late June or early July, but the percentage of success is considerably lessened.
To obtain a sizable root ball is not as difficult as it is to successfully overwinter the transplanted cutting and get strong growth the following spring. This can only happen providing there was growth started and/or swelling of the growth buds on the young plants before dormancy set in. Again, timing is very important! If three or four-year-old plants are potted up, wintered over in a cold, holding house, and heat turned up in early March, by mid-April a good, strong set of cuttings can be taken from them which will root and be ready for potting by mid-June. Two months' time remains then in summer for growth, thereby giving more than enough time for a good set of shoots to form.
Plants grown as stock plants should be maintained in a vigorous, healthy condition. An early spring application of fertilizer is recommended. After blooming, all blossoms must be removed so there can be no seeds formed, as they do not come true. To make this chore easier, remove 90% of the blossom buds in late fall after all leaves have dropped. The plants should also have a yearly pruning by removing the oldest canes at ground level. This will force new growth at the base of the plant. Cuttings root more readily from these young shoots.
Cuttings are taken one day, preferably early in the morning, placed in closed plastic bags and refrigerated for a day or two prior to preparation. They are then in a more turgid condition for sticking than if they were prepared immediately after removal.
When propagating deciduous azaleas, the terminal growth bud and the lowest leaves are removed. The stem is wounded on both sides, as is done with rhododendrons. This wounding is done here not with a sharp knife or pruning shears, but with a potato peeler obtained from any hardware or grocery store. Not only does the blade remain very sharp, but the wound is the correct depth - just to the cambium layer. A light dusting with a 0.8% indolebutyric acid (Hormodin #3) is made prior to sticking in a pre-dampened medium of peat and perlite (1:2) and placed under intermittent mist.
When wounding deciduous azaleas or any other cuttings, I always try to avoid cutting through any nodes on the stem where leaves have been removed. This is where a new shoot below ground level may appear and form the foundation for a well-branched plant.
If sufficient material is available, a branched cutting can be made with a ˝ in. stub of old wood. Each of the green shoots should be wounded. This is more difficult to prepare and extravagant of material, potting medium and space, but will produce a beautiful plant in a year's less time.
Elongation is obtained if potted transplants are placed under lights for forcing. This has been claimed to be the only way to have success. But in this age of high electrical costs, who can afford the price? Or, if you could who would buy your plants, for they would be priced beyond what the general public is willing to pay?
After rooting and potting the plants, place them outdoors in the open under lath or shade cloth for approximately one week. Then remove the shading and leave them in direct sunlight, and let the bright sun, instead of electric or fluorescent lights, do the work of forcing for you. I use a premixed potting medium containing bark, to which I add additional perlite (5:1), Osmocote, MicroMax, and a wetting agent. All young plants are watered daily or as needed, early in the morning. Under these conditions we expect six inches of new growth, occasional budding and one, or sometimes two, new shoots from below ground by fall.
When potting up rooted cuttings there are often some that have not yet rooted but are still in good condition. These are restuck and left under mist for about one month more. The greater majority are rooted by then. Those still not rooted but in good condition are restuck again, placed under a bench or outside in the fall in the woods or under lath and forgotten until the following spring. Most will then be rooted and, though small, will grow normally by summer and will be salable a year later than the group with which they started.
The rooted cuttings can be wintered in a cold greenhouse, about 40°F, until their dormancy period is satisfied. About mid-February the temperature should be raised to about 60°F to force growth. Occasionally as new growth starts and shoots are about ˝ in. in length, they become limp, flop over and die. Spraying with Benlate will counteract this condition, which can rapidly spread through the entire house if not corrected. Be certain that the Benlate is fresh for it loses its effectiveness if over two years old. Also good air circulation in the greenhouse is very important. For this reason, I much prefer to winter deciduous azaleas outside as they are completely hardy. This will delay spring growth but there will be more salable plants in the long run.
A lath house, 16 ft. wide by 48 ft. long by 8 ft. high was built here this summer to hold our potted transplants. The first two feet above ground level of the sides are covered with used plastic (later to be replaced by clear corrugated fiberglass, which will be removed in summer) to act as a windbreak. The rest of the sides, as well as the entire top, are covered with snow fencing. This allows rain and snow to penetrate and protect the young plants all winter and spring.
Many deciduous azalea cultivars are susceptible to mildew in summer. While this can be easily corrected with a Benlate spray, it is just another chore for either the nurseryman or the homeowner. Make your original selection carefully. Although many flowers are look-alikes some cultivars get mildew consistently while others never get it. I have found the hairy-leaf ones get it and the smooth leaved ones do not. The latter not only look better all summer and need no spraying, but they also hold their foliage two or three weeks longer in the fall.
In New Jersey, we have the double problem of Japanese beetles and gypsy moths. A yearly spraying with Sevin in late May counteracts the leaf-eating damage caused by these pests.
The Ohio Agricultural Research and Development Center, Wooster, Ohio has reported that willow cuttings, soaked in water for 48 hours, give off a compound that makes hard-to-root plants root more readily if the cuttings are first given a 24 hr. presoak in this solution before sticking. This will be tried before next year as a few select cultivars are consistently difficult to root.