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The water supply of my community is soon to be fluoridated, with a resulting fluoride concentration of one part per million. What effect if any will there be over the long term by irrigation of rhododendron with such treated water? - Canton, Mass.

Plants differ in their sensitivity to fluorides. There is a possibility that after many years of irrigation that the fluoride concentration could accumulate to a toxic level. The toxic effect manifests itself as a slight cholorsis, followed sometimes by premature defoliation. Fluorides seem to be absorbed by the leaves through the cuticle and trans-located to the leaf margin and tips. When a toxic concentration is reached, the cells of the epidermis collapse and die.

I might point out to the writer of this question that the fluorides emitted from smoke stacks of factories and spread by diffusion or carried by air currents in many cases exceed the concentration of fluorides in the drinking water. Widespread damage is caused to plants each year by air pollutants such as hydrogen fluoride (HF).

The effect of air pollution on growing plants has concerned me for some time; I guess because I live in an industrial area. This might be an appropriate topic for an article in the Quarterly Bulletin in the future. - Fred R. Davis, Kent, Ohio.

I read once that azaleas do best in pots when they are root bound. I would like that confirmed by someone who has raised azaleas in pots.  I'm beginning to think that I'm the only one who does. I set the pots out during the summer on cement blocks, but at fall I bring them inside and force them under Gro-lights for winter bloom. The azaleas are in six-inch pots. I already have a lack of room problem, but if I went to larger pots I'd have real trouble. - Wickes, Ark.

In answer to your question about azaleas doing best when root bound, I certainly think you can reach a limit to this where actually they would start declining. They can be kept fairly confined in small pots with adequate fertilizer and water. However, we do like to repot our plants on an annual basis, much like some of the Bonsai are handled, removing some of the root mass, adding peat and organic matter to the same size pot and reducing some of the top growth. Eventually, the plants may get too large to continue doing this and you may find it desirable to shift. But in repotting each year, generally after they finish flowering, this method proves satisfactory with us.

It is somewhat difficult to anticipate when to repot some of the Satsuki cultivars which flower later, so we repot these before they start new growth in the spring and before we begin to force them. - Fred Galle.