QBARS - v17n2 More About Lime

More About Lime
Carl Phetteplace, M.D., Eugene. Oregon

It seems almost absurd to offer more to the Bulletin on the subject of "Liming Rhododendrons." There is only one reason for my considering it. On different occasions Dr. Clarke has commented on the rapid growth in membership of the A.R.S. in the past few years. This of course means many new members who are perhaps just learning about rhododendrons. They naturally are eager for any information they can come by as to how to grow their plants better. Likewise they would consider almost anything appearing in the official publication of the Society as generally applicable.
Unless I misunderstand a number of Alleyne Cook's* statements about lime, such as his disregard for pH values and the report that his rhododendrons thrive in sand when lime is added, it would seem that some answer should be made to prevent members from being misled.

* "Lining Rhododendrons", Alleyne Cook, A.R.S. Bulletin, Vol. 16 No. 2.
"Liming Rhododendrons" Part II, Alleyne Cook, A.R.S. Bullletin, Vol. 17 No. 1.

First, I must say that I have a high regard for Alleyne Cook and am fond of him personally. My visits with him have always been interesting and informative. I believe he has had good basic training in horticulture and gardening, something most of us rhododendron "buffs" have not had. He has grown and observed the growing of rhododendrons over a large part of the world. No one can disagree with him that if a plant looks good and is growing satisfactorily it should be left "as is."
It is true that calcium is required for good rhododendron growth. Lime would supply this need, but the amounts needed only fall into the category of "trace elements" along with magnesium, iron, manganese, sulphur and others. Although calcium is usually present in adequate amounts in soil, it may at times be leached out especially in porous soils.
Again I am told that it is possible that under certain circumstances a soil may become too acid - i.e., the pH becomes so low that some nutrient elements, iron especially, are not released to the plant, or that there can be an imbalance in the calcium-magnesium ratio preventing good health. All these things can be corrected by the addition of calcium as lime. However, lime is an alkaline substance and as such can neutralize the soil acids and even bring the pH ratio to the alkaline side.
I wonder if it may be that Mr. Cook's conclusions are clue to having had some of these conditions that are so promptly relieved by the calcium, and hence improvement in the plants' appearance; possibly the effect of the lime has not been present long enough to show its real effect. If this is so the follow-up reports of the plants "dressed with lime" would be interesting.
It might be well to remind those who may be intrigued with these reports that for more than a hundred years scientific work has been carried out in many parts of the world, carefully analyzing the soils where rhododendrons were thriving. Likewise studies on plant tissues in health and in sickness to determine what is optimum and the effects of deficiencies have been done. Such work has been and is going on in many laboratories of colleges and agricultural experiment stations in various states and countries. There has been no important variance in the findings. Rhododendrons generally prefer an acid soil and will soon look bad in an alkaline medium. Work in this field has been well reported by David Leach in his monumental book, "Rhododendrons of the World." I am sure one can safely accept and follow these findings.
Most of us have had a sad lesson or two with lime by trying to grow some nice rhododendron too close to the house where the ground had been limed by the spilling of plaster during construction. All along I have had just a little suspicion that Mr. Cook is not really as serious about this lime business as it appears, but is trying to have some fun and stir us up a bit. If so that is good, and I have "taken the bait."
Let us hope, Mr. Cook, that your limed rhododendrons always keep as vigorous and full of life and interest as you do, and that you will keep us informed from time to time on your progress with the long term effects of dressing your rhododendrons with lime.