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Elisabeth C. Miller Library

Keyword: Plant-water relationships

Spitting Rhododendrons

Why are my rhododendrons spitting water? On hot sunny days this summer, we’ve been sitting in their shade and noticing occasional tiny needle-fine droplets landing on us. Is this caused by insects (I don’t see obvious signs of them on the leaves), or is it normal?

 

My hunch is that the leaves are transpiring. I found an article by Bill Letcher in the Journal of the American Rhododendron Society (vol. 41, no. 2) entitled “Rhododendrons with a Drinking Problem.”

The article is about the importance of water in successful rhododendron cultivation, but also does a good job of explaining transpiration:
“The water absorbed by the root hairs, or rootlets, is drawn up in the stem of the plant and into the leaves, where it exits via small holes called stomata into the air as vapor. This process is called transpiration […] Transpiration requires a lot of energy, and this comes, as we might expect, from the sun. If all else is equal, transpiration amounts are directly proportional to the amount of radiant energy striking the leaf surface of a plant: the more energy, the greater the amount transpired. […] One factor of paramount importance to rhododendron growers which effects transpiration is the relative humidity of the air surrounding the leaves. Dry air causes appreciably more transpiration than humid air, and the presence of wind increases this dramatically by replacing the layer of air next to the leaf surfaces before it can become saturated. Ambient air temperatures will also markedly increase transpiration as they rise, sometimes with disastrous results. Our family of rhododendrons has less ability to extract moisture from the soil than, say, manzanita (which can pull all of the available water from the soil down as far as six feet!).”

If we have more hot weather, you may want to give your shrubs an occasional supplemental drink of water, since they are shallow-rooted, and our summer-dry climate (depending on how hot and dry it is) can cause stress to the plants. Keep an eye on how they are looking and do what you can to maintain their health (and preserve your shady refuge!). To quote Letcher again:
“The family of rhododendrons has either never been forced to adapt to very low available moisture conditions, or has not adapted well to them. Their roots tend to be quite shallow. The foliage is lush, dense, and of a dark, absorptive color instead of being light and reflective of the radiation. They display their displeasure with your attempts to wean them from the conditions they most enjoy, by doing exactly what a great many other plants will do: they shorten their internodal growth, reduce the number and size of their new leaves, drop some of their older leaves, and just plain sulk! Ultimately, they languish into a pitiful state of scrawnyness and pallor which is not a pleasant sight in your garden.”

 

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Tomatoes and blossom-end rot

It’s summer and my husband wants to add lime to our soil because some of our tomatoes have blossom-end rot. He thinks this will correct the problem. I think we would do better to make sure our tomatoes aren’t drying out, and then work in soil amendments next time around. Also, couldn’t we use eggshells for calcium instead of lime? We have a ready supply from our backyard chickens!

I think you are on the right track. Blossom End Rot (BER) is a physiological disorder that tends to affect larger tomatoes rather than smaller ones. According to Craig LeHoullier’s book Epic Tomatoes (Storey Publishing, 2015), some varieties are especially susceptible: “Roma/paste varieties, and some of the longer indeterminate sauce types like Opalka and Speckled Roman. Adverse growing conditions [such as drought stress or low calcium levels] can make it problematic for many other varieties as well.”

All print and web sources I consulted mention environmental conditions as a cause of this problem. It starts through the supply of water and calcium in the developing fruits. The effects may be seen on plants exposed to a period of drought during rapid growth; root damage; heavy, wet, or cold soil; excess salt in the soil.

A soil test is the ideal starting point to make sure the pH is adequate for tomatoes. Epic Tomatoes recommends amending the soil with lime if necessary. (Washington State University Extension says the time to do this is 2-4 months before planting, not in the middle of summer!) Mulch around the base of the plants to conserve soil moisture during hot spells and water regularly. Another reason a soil test is a good idea is mentioned by British Columbia author Linda Gilkeson in her book Backyard Bounty (New Society Publishers, 2011):

“Your soil might have enough calcium, but it isn’t available, or the plant can’t take it up fast enough. This is often because the movement of calcium inside the plant has been inhibited by drought stress, possibly from irregular watering. This is often seen on tomatoes in containers that experience alternating dry and wet soil. It can also be caused when plants grow too fast as a result of too much nitrogen fertilizer.”

Since you prefer not to use lime (the dry powdery texture of calcium carbonate can be irritating to the skin and eyes), you will be pleased to know that the use of eggshells is mentioned by Mike McGrath in You Bet Your Tomatoes! (Rodale Press, 2002). At planting time you can “put some crushed-up eggshells into the planting hole.” Make sure the eggshells are ground to a fine consistency.

Don’t forget that those damaged tomatoes can still be used–just cut off the bad parts!

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