QBARS - v15n4 Summary of Replies to Questionnaire on the Best Rhododendrons, Azaleas and Methods of Cultivating Them in the Region Served by the Great Lakes Chapter

Summary of Replies to Questionnaire on the Best Rhododendrons, Azaleas and Methods of Cultivating Them in the Region Served by the Great Lakes Chapter
David G. Leach

EXPLANATORY NOTE: In attempting to tabulate the replies to the questionnaires which were distributed a few months ago it soon became apparent that the climate extremes within our region made it imperative to classify the information according to the climate from which it came. Accordingly, the completed questionnaires were divided into two groups: those represented by zone 5b on the new plant hardiness zone map of the U. S. Department of Agriculture, and those which came from zone 6b of the new map, which is much more accurate than the old.

Zone 5, then, as it is used below, is the "inland" region, 10 miles or more away from the Great Lakes, in New York, Pennsylvania (excluding Allegheny and Cambria counties), Ohio and southern Ontario. In Michigan it refers to the inland communities south of Port Huron but also to the lake shore area north of Port Huron.

Zone 6 includes the regions within 10 miles of any of the Great Lakes (except north of Port Huron in Michigan) plus Allegheny and Cambria counties in Pennsylvania.

The reports seem to come clearly from one zone or the other, and the arbitrary selection of a 10-mile limit from any of the Great Lakes appears to apply quite well for this purpose.

This information should be of great value to our members and all are urged to preserve this report as a guide in purchasing Rhododendrons and Azaleas and in their cultivation of these plants. I have taken an editor's privilege of inserting comments in cases where the tabulation of the data alone does not reveal all of the useful information derived from it. Such comments are clearly identified in each case.

The response to the questionnaire was gratifyingly large and reflected the cooperation and enthusiasm of our members which we have come to regard as a permanent characteristic of the Great Lakes Chapter.

The ratings following the color descriptions of both hybrids and species are those of the American Rhododendron Society as published in Rhododendrons 1956 as follows:

Those not rated were too new or were not grown widely enough to evaluate in 1956 when the ratings were last published.

EDITOR'S NOTE: The designation of bud hardiness as poor, fair or good is on the basis of the average. For example, if nine growers rated a clone "good" and one rated it "fair," the majority evaluation appears. If there was a sizable minority opinion, it is represented, with the majority, in "fair to good."

It is apparent from the replies that growers in Michigan prefer less sun than those elsewhere; one remarked that he would eliminate winter sunlight entirely. It is equally apparent that zone 6 growers elsewhere who are in a climate strongly influenced by the Great Lakes, prefer a good deal more exposure for their rhododendrons, probably because higher atmospheric humidity and a lower general light level makes this possible.

Editor's Note: Parentages and color descriptions in the foregoing lists are taken from The International Rhododendron Register. Many growers recommended shade to some extent for deciduous azaleas primarily to prolong the time the flowers are in good condition, especially for the newer British hybrids. Some shade for persistent leaved azaleas is described as aiding the plants to retain their flower buds in good condition through the winter.

Soil Preparation

Among the growers using the conventional ingredients of topsoil, peat and sand, the mathematical average of proportions for the mix giving the best results:

50% Topsoil  39% Peat  11% Sand

Among the growers using additional ingredients, the mathematical average of proportions for the mix giving the best results:

18% Topsoil  30% Peat  18% Sand  34% Other Humus Sources (Leaf Mold, Compost, Rotted Sawdust, Rotted Manures)

EDITOR'S NOTE: There was provision on the questionnaire to indicate "No special preparation-natural soil without additions." Among all of the replies only two growers indicated that their natural soil produced satisfactory results without modification.

Mulching

The mulches which produce the best results listed in the order of frequency mentioned, with the depth of the mulch stated as a mathematical average of the replies:

Oak Leaves, 4"

Ground Corn Cobs, 1"

Sawdust, 2"

Peanut Shells, 2"

Peat, 2"

Pine Needles, 3"

Serve-All, 1"

Black Polyethylene Plastic

Wood Chips or Shavings, 3"

EDITOR'S NOTE: There was provision on the questionnaire to indicate that no mulch is used. Not one grower indicated that he cultivates rhododendrons or azaleas without a mulch.

Watering

Since municipal water supplies are usually neutral (pH 7.0), the question was asked "Do you use city water or a natural source of water?" The responses:

55% City Water

45% Well, Pond or Stream

Apparently there is no difficulty from loss of soil acidity clue to the use of municipal water, although the surprisingly large percentage of growers who use a natural source of water did not state that this had anything to do with their reason for doing so. All members indicated that they do irrigate their plants. It is usually thought that irrigation of Rhododendrons and Azaleas during the month preceding the first expected frost impairs their hardiness by diluting the carbohydrate concentration in the sap. The question was therefore asked: "Name the latest date in the season prior to frost that you consider it safe to irrigate." The answers, average mathematically:

Zone 5: August 14th

Zone 6: September 6th

Fertilizing

The fertilizers which produce the best results, listed in the order of the frequency mentioned:

Ammonium sulphate

Cow manure

Cottonseed meal

Agrico for Broadleaf Evergreens

Westcroft's Greenleaf Compound

Kapco Evergreen 7-7-7

Sheep manure

8-6-6

Eastern States Starter

G. & O. Azalea Fertilizer

Ammonium Sulphate plus 0-25-25

Cottonseed meal plus 0-15-15

5-10-5

30-10-10

8-8-8 (organic)

16-8-8

6-8-0

Ureaform

It is usually thought that fertilizing Rhododendrons and Azaleas within 60 clays of the first expected frost impairs hardiness by stimulating unseasonably late growth. The question was therefore asked, "Name the latest date in the season prior to frost that you consider it safe to fertilize." The answers, averaged mathematically:

Zone 5: July 15th

Zone 6: June 18th

EDITOR'S NOTE: There was provision on the questionnaire to show that the grower did not use any fertilizer. Only one did not. It is interesting to note that growers in zone 6, where the first frosts are a good deal later than in zone 5, are much more conservative in extending the season of fertilizer use. Many of our members in zone 6 are professional growers.

Spraying and Dusting

The insecticides which produce the best results, listed in the order of frequency mentioned:

Malathion

DDT

Dieldrin

Lindane

Aldrin

Aramite (miticide)

Nicotine and soap

Methoxychlor

Tedion

Vapotone XXX

DX

The fungicides which produce the best results, listed in the order of frequency mentioned:

Captan

Fermate

Sulphur

Parzate

Karathane

Fixed Copper

EDITOR'S NOTE: Malathion as an insecticide and Captan as a fungicide has no serious competition in the preference of growers. 23% of the growers stated that they do no spraying or dusting whatever.

I recommend that the portion of the survey relating to the bud hardiness of rhododendrons and azaleas, both hybrids and species, be repeated in 1963. Many growers commented that they had not grown some of the newer hybrids and rarer species long enough to have a valid opinion of their bud hardiness, and declined to rate them until they had more experience with them.