Eastern Rhododendron Observations
David Leach, Brooksville, Pennsylvania
I have very few observations of practical value, but among them would be that nurserymen in the East unintentionally mislead their customers with respect to advice on sites for planting rhododendrons.
The rhododendron nurseries in the east are located near bodies of water (on Lake Erie) or close enough to the coast that their climate is modified by such a location. When they sell to customers inland they use their own climate as a guide and generally advise planting sites considerably more exposed than is desirable for inland gardens. The presence of abundant moisture in the atmosphere near large bodies of water makes the plants in the nurseries better able to stand exposure than is the case for conditions inland, where rhododendrons should be placed in sites with considerably more shade to compensate for the lower humidity and clearer, brighter atmosphere.
Also, I think a good deal less of sawdust as a soil amendment than formerly. I use it constantly as a surface mulch but I am going to abandon it as a source of humus to modify the soil structure. The results just are not as good as is the case when peat is used, and it seems to be largely a matter of the difference in the moisture-holding capacity of the two materials. The nitrogen supplement is absolutely necessary .when using sawdust. It does not seem to affect the pH of the soil at all.
Our climate here is very severe, with temperatures to 20° below zero, but the soil is naturally acid and R. maximum and R. roseum occur abundantly in nature. I have been trying to develop superior azaleas and rhododendrons suitable for our .climate here, and have made some modest progress. For example, I have a plant of 'Catawbiense Album' x R. fortunei which is ironclad and has slightly fragrant, bell-shaped flowers, pure white and of good size. It is definitely superior to 'Catawbiense Album', heretofore the best white for our climate. I would not make that cross today with any expectation of substantial progress in the Fl generation. As a matter of fact, the plant of R. fortunei was not even the selected hardy form.
It does seem apparent that the stability of the genes is less tenacious when exposed to the multiple effect of two primary hybrids, with four species represented in the two parents; and that results can be expected to be progressively less promising after the F2 or possibly F3 cross. The lack of precise scientific data on inheritable factors in such an important genus is really rather astonishing. If these fellows who are old hands at the game have made reliable observations on such things as linkages, dominants, etc., I wish they would publish them for the benefit of the rest of us. Since some crosses are not generally looked' upon with favor in the genus, somebody is going to have to undertake a massive program entirely without regard to ornamental value of the results, to come up with the information which would be of inestimable value to all of us.
I find the Glenn Dale propagator an ideal convenience both in starting seedlings and for rooting cuttings. It is an enclosed case about 6' x 3' x 4'. The flats rest on an open framework beneath which is a heater controlled by a thermostat. The front of the case is two glass doors. Light is provided by a large fluorescent fixture, 24 hours a day, using blue tubes for seedlings, pink for cuttings. Humidity, temperature and light quality are thus controlled very closely and the results are unusually good. I grow the seedlings in pure sphagnum moss, and feed them artificially. I have the propagator in the basement of my home. It eliminates the need for a greenhouse as the seedlings can be grown along in it for months, until time to put them in the cold frame for wintering-over. "Plant Propagation Under Fluorescent Light" (November, 1945) issued by U. S. Dept. of Agriculture, Agricultural Research Administration, Bureau of Plant Industry, Beltsville, Md., gives full details.