Azaleas for the Arid Southwest
Ross M. Nelson, San Antonio, Texas
San Antonio is located near the Eastern edge of the arid southwest and roughly on the border of Zones Eight and Nine. This is more easily explained by saying that in some ancient time we would have been a sea port on the Gulf of Mexico. Now we are 150 miles inland and on the edge of President Johnson's hill country. This leaves the city proper and areas South at an altitude of about 600 feet and definitely Zone Nine. Beginning at the north side of the city the land rises abruptly into hills varying from a thousand to fifteen hundred feet and averaging ten degrees cooler winter and summer, Zone Eight.
Summer temperatures reach a reliable ninety degrees with the humidity almost seventy percent if the wind is from the Gulf or down to fifteen percent if it is from west Texas. Winters are quite mild with only occasional dips to twenty-five degrees but with frequent fog and drizzle. The rainfall average for the last eighty years was only 28 inches. This includes a low of 13 inches and a high of 50 inches. Most of the rain falls in April-May and September-October.
The soil from here to the Gulf is sandy loam, slightly alkaline and of low fertility. Up into the hill country it is very alkaline, consisting of a thick clay, called Caleche by the local residents from the Spanish for 'color of milk'. This is freely interspersed with a porous limestone and flint.
Culture of azaleas in either of these soil types is quite trying. In the clayey areas all plantings have invariably been at the normal grade. Usually some effort has been made at planting time to provide drainage and to make the soil more friable.
Feeding of the plants in most instances is non-existent. Quality of the plant is quite apparent with those gardeners who regularly apply the commercially prepared Azalea-Camellia foods and deteriorates rapidly through those who rely on decomposing mulches alone to those who do no more than diligently apply the dregs of the dill pickle jar with an air of confidence in the age-old home remedies.
The search for a heat tolerant, drought resistant evergreen azalea, that doesn't mind being planted in a heavy alkaline soil, becomes exasperating at times. Actually most of the Southern Indica varieties fall within this category with only minimal care. The great difference occurs in the degree of satisfactory performance set as a goal by the gardener himself. To compare the springtime inflorescence of the single clone 'Formosa' as grown by the average gardener in the San Antonio area with the same clone in areas along the Gulf Coast is virtually impossible. I doubt that a traveler from the latter area could readily distinguish between 'Formosa' and other similar clones such as 'Fisher's Pink', 'Pride of Mobile' or 'Lawsal', even though they were performing entirely to the satisfaction of our local gardeners.
This is not to infer any less interest in azaleas here than further East but to illustrate the degree of acceptability between the areas. Whereas the Gulf coast has nearly ideal conditions to produce a beautiful specimen, here it takes considerable attention if the gardener wants anything more than a twiggy, sparsely leaved, and somewhat chlorotic plant that blooms with effort in the spring.
Of the Azaleas being grown in my yard there are but two common cultural factors; they are all grown in-grade and all are mulched with two to four inches of coarse shredded pine hark. Several plants of 'Formosa' were planted differently with feeding as described below to see just what was the hest method.
Three plants received no soil preparation whatsoever other than that a three ft. wide, by two ft. deep hole was dug and rock and fallen leaves added to the bottom six inches for drainage. Two were planted in identical sized holes, one with half humus peat soil and half top soil, one with half coarse sphagnum moss and the other half top soil. Little difference can be noted in growth, form or bloom, showing they are adaptable if properly fed.
Feeding is done twice a year. This consists of one-half cupful of ammonium sulphate and one-half cupful of super-phosphate, along with one-half cupful of ferrous sulphate, in the early fall; in late spring, after blooming, they are given only the same amount of ammonium sulphate and ferrous sulphate. The Rhododendrons have received the same treatment as the Azaleas and have so far responded well though they have been planted only two to three years.
Rhododendrons Now Being Tried
Few rhododendrons were grown in this area until recently, and I have not located any plantings over three years old. This is a bit too short a period to come to any definite conclusions as to their ability to survive here. All plantings I have seen, including my own, are on the North side of the house and in fairly heavy shade with direct sun only for a few hours in the early morning.
The plants now in cultivation here are as follows; R. catawbiense , R. maximum and 'Autumn Gold' are planted in-grade. R. arboreum , R. fortunei and 'Lee's Dark Purple' are being grown in pots.
One local resident, Christine Ressman whose home is on the far north side of the city, has two fine examples of 'Jean de Montague'. One is grown in a basket filled with humus, against the house, and the other above grade under the trees in the yard, along with a plant of 'Fabia', which is doing equally as well.
Azalea Varieties Being Grown
Most Azaleas grown here are of the Belgian Indicas or Kurumes and only infrequent appearances of the other groups. The following are plants seen locally, including those I am growing in my own garden;
Southern Indica: 'Pride of Mobile', 'Duc De Rohan', 'Elegans', 'Fisher's Pink', 'Formosa', 'George L. Taber', 'Iveryana', 'Lawsal', 'Mrs. G. G. Gerbing', 'Presidente Claeys', 'Pride of Dorking', 'Prince of Wales' and 'Southern Charm'.
Belgian Indica: 'Albert Elizabeth', 'Dr. Bergman', 'Eric Schaeme', 'Jean Haerens', 'Mme. Petrick', 'Orchidiflora', 'Prof. Wolters'.
Species: R. phoeniceum , R. mucronatum , and R. indicum .
Rutherford: 'Alaska', 'Christmas Red', 'Dorothy Gish', 'L. J. Bobbink', 'Pink Ruffles' and 'Rose Queen'.
Kurume: 'Azuma-Kagami' ('Pink Pearl'), 'Coral Bells', Cattleya', 'Hinode-giri', 'Ima-shojo' ('Christmas Cheer'), 'Suetsumu' ('Flame').
Others: 'California Sunset', 'Miss Cottage Garden', 'Hexe', 'Pinocchio', 'Firedance' and 'Martha Hitchcock'.
Other than the two deciduous azaleas I planted this year I know of no others of this group being grown in this area.
Fig. 23. Azalea 'Memoire John Haerens' blooming in
the author's garden.
Breeding for Local Adaptation
I think it is entirely possible, with careful selection of parent plants, and many successive generations, to breed a race of plants with a slow metabolic rate, and extensive root hairs to exist without mycorrhiza, in an adverse climate such as this.
Having read of the experiences of some orchid species collectors who resided in adverse climates, I began raising Azaleas from seed primarily to test one of their theories. This, briefly, is that, although the mature plant is not readily adaptable to a less amenable climate, it's seedlings sometimes are. This, I found out later, is basically what breeders in the northern states have been doing to develop cold hardiness.
Having been a member of the A.R.S. only a short time, and not having been in contact with other breeders to any great extent, I have many times gone off on un-productive tangents that have not been very fruitful except in producing some genetic oddities.
Fig.21. Different types of plants resulting
from chemically induced, self
fertilization of azalea 'Pride of
One of these continues to fascinate me although it apparently is of no practical value in the breeding program. It is a plant resulting from chemically induced self-fertilization of 'Pride of Mobile', (evergreen Azaleas are normally self sterile), which could best be described at first glance as a columnar Azaleodendron. This seedling batch produced many weak plants but also the most extensive variety of growth forms I have ever seen, from dwarfs that never grew over two inches tall through some with variegated foliage to a few normal ones.
From this and a few other enlightening experiences I have learned that to achieve my goal it takes time and many successive generations of cross breeding to find the plant that doesn't mind if the soil is alkaline, the water alkaline and the humidity virtually nonexistent.
Here is a brief description of the methods presently being used in an effort to arrive at the desired goal.
To gain time some varieties were potted and forced into bloom, December through January. This isn't too difficult as many Belgian and some Southern Indicas frequently bloom in the late fall here. All crosses were properly tagged and the plants kept in active growth on the dirt floor of the green house while waiting for warmer weather to set them outside. About the end of February and well into early March the remainder of the plants left outside were well in bloom and a few additional crosses were made. The first few crosses were protected by small plastic bags to guard against accidental insect pollination. This I have found to be quite unnecessary as over the years I don't think I have found more than two or three seed pods that didn't have an identification tag attached. Apparently this locality doesn't support the insect life capable of carrying adequate pollen amongst the Azaleas.
The weather hasn't been too much of a factor in the ability of the stigma to accept pollen. The only thing noticeable is that periods of extreme low humidity shorten the period of receptiveness of the stigma. These same periods also seem to dry the pollen at the apical pore and necessitate carrying a small scalpel along to sever the super-most portion. Re-pollination has rarely been necessary and was done only if the flower had not wilted by the end of the second day.
The seed capsules are picked when they are still green. This is approximately the early part of May for the forced crosses and early June for the outside crosses. This point is identified when the pistil has completely dried and the sepals have only begun to turn brown. They are then placed in two inch diameter plastic containers, with covers, such as are used for small parts, screws and etc. The information on the tag is transferred to a dry-adhesive gummed label which is stuck to the container for ease in identification. The containers are then stored on an upper shelf of the refrigerator at about 45 degrees for fifteen to thirty days. They are then removed and allowed to dry for two or three additional days before opening the containers. At the end of this time most capsules have begun to split open. The seeds are then cleaned as carefully as possible and stored in the same marked containers until sorted for personal preference, necessary for future breeding, and excess.
The seeds are then sown in 5x7x2 inch trays, beginning in early August and continuing through September as time permits. In some instances, depending on the importance of the cross, more than one tray of a cross has been sown. All trays are marked, on 3 inch pot labels, with both the female and male parent, and date of sowing.
The sowing medium has been varied considerably but at present I have settled on a fifty-fifty mixture of milled sphagnum and perlite for the first inch and a half from the bottom.
This is covered with about one-eighth to one-quarter inch of milled sphagnum alone. All is wet thoroughly, at time of mixing, with tap water to which has been added one level tablespoon per peck of Teratan, a commercial preparation of Terachlor and Captan, along with one level teaspoon of a balanced soluble fertilizer such as Hyponex.
The seeds, having been broadcast thinly, are settled in by a heavy misting from a hand misting device. The trays are then placed in plastic bags, two side by side since I have available heavy freezer bags large enough for this purpose. The bagged trays are then placed on the greenhouse bench, without the benefit of additional shading, as the house is covered with corrugated translucent plastic. Although there is a small evaporative air conditioner in the greenhouse, the ambient temperature at the level of the benches has risen to as much as 105 degrees for several days at a time. This excessive temperature is modified somewhat by having the benches filled with a mixture of humus peat, soil and sand which is kept wet. The night-time low normally runs from 75 to 80 degrees. Seedling batches have been germinated during most all seasons of the year but I find the results far more acceptable from those sown during the late summer months. This season was tried initially to prove a vague theory that heat tolerance was present even in the seeds' ability to germinate under high temperature, but I found the percentage of germination highest in these batches and it proved very little.
Fluorescent Lights Used
Most of the seedlings are grown under broad spectrum fluorescent lights, from a few days after germination until nearly a year later, when they are potted and moved outside to make more space.
One bench has the lights eight inches above the trays and is completely enclosed in polyethylene sheeting, with a fan for circulation, to retain moisture and maintain humidity. The plants are left here until they have formed the fourth or fifth set of leaves, the plastic bag having been removed after the second set of leaves, in slow exposure periods over three or four days. The seedlings have not been thinned nor transplanted up to the time they are large enough to plant into the second bench. This may seem a large size for transplanting from a tray but I have lost but few to the drastic root pruning and it even seems beneficial in stimulating their growth activity.
The second bench also has the lights on continuously but they are located fifteen inches above the soil level. This bench is filled with coarse milled sphagnum, perlite and humus peat soil each one-third part. They remain here, receiving the same balanced Hyponex fertilizer with every-other watering, and judicious tip pruning, until late the following spring when they are about four to eight inches tall and well bushed out. They are then potted for removal to the outdoors. Potting is necessary as I live on a small city lot and have far from enough room for planting in the ground. Luckily damping-off, with the precautions taken and the alkaline water, has not been a problem.
Though progress has been slow so far I do have a few promising plants and perhaps in a few years I may have something vaguely resembling an azalea that likes to live in the Southwest.