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Tuesday - September 27, 2011

From: Austin, TX
Region: Southwest
Topic: Transplants, Watering, Shrubs
Title: Has overwatering harmed cherry laurels in Austin?
Answered by: Barbara Medford

QUESTION:

I am so upset. I know we've been having a terrible drought this year in Austin, and I've been trying to balance water conservation with protecting our recent very large investment for massive landscaping at our new construction. We did plant all non-invasives, mostly native. Our two 5' tall Cherry Laurels have been doing ok in a part shade/part sun raised bed at the east-facing end of our patio - but all plants are taking a beating these days. Friday I treated them to an extra long gentle soaking. Today (Sunday) I went to visit with them and was astonished that the vast majority of leaves have turned brown. Almost overnight! Coincidence? Or did I shock them when I gave them that soaking? THANKS for any insight!

ANSWER:

Begin by following this link, Prunus caroliniana (Cherry laurel), to learn what this plant ordinarily requires in terms of shade and watering.

When we are spending so much time answering questions on what to do about the drought, we were a little slow to grasp that over-watering could cause a result very similar to under-watering. To our surprise, searching on the Internet yielded a number of references on the subject. We selected two articles to refer you to, and suggest you read all of both. While the first one, Is Over-Watering Harmful? is from the UK, we felt it still applied to your situation.  From The second article, from Green Thumb Articles, Garden Irrigation, we extracted the following paragraph:


"Irrigation alters two parameters in the soil. First, obviously and self-evidently, water is added to it; less obvious, but no less critical, is that the percentage of oxygen present in the soil is subsequently reduced. As the plants are dependent on both a ready supply of oxygen in the root zone, together with adequate moisture, it follows that correct irrigation practice, always takes account of both these factors. Over-watering therefore, could more accurately be termed, 'lacking in air'."

The early leaf browning and drop of your shrubs can certainly be largely attributed to the drought, but the sudden infusion of water, essentially closing out the oxygen also needed by the roots, certainly didn't help. We don't think you killed the cherry laurels, but if they are in clay soil without any compost or other amendments to make the drainage more efficient, watering the plants becomes even more critical.

We recommend you consider how good the drainage is by filling a shallow depression with water and observing how quickly it disappears. If it takes more than a half hour to drain away, you do have a drainage problem. While it's a little late now to add amendments to the soil to improve drainage, you can certainly modify your watering practices. Any new plant, particularly a woody plant, is very susceptible to transplant shock. Transplant shock is almost inevitable if you plant in blazing hot weather. In particular, woody plants should be planted in Texas in the Winter, when they are semi-dormant. Rather than failing to water and then overwatering, it would be far better to stick a hose down in the soil near the trunk and let it dribble slowly for about a half hour, twice a week; this should continue for several months unless ample rains have returned.

Finally, have you lost your plants? Try the thumbnail test, beginning fairly high on the branches, scratch off a very thin sliver of the skin. If there is a thin layer of green beneath, that tree is still alive. If you do not encounter green up high, keep moving down the plant to the root area. Plants in a stressful situation often protect themselves by dropping leaves to reduce the load on the roots and vascular system. Those dead leaves will not turn green again, but when it is leafing out time again, probably in the Spring, you should see the plant begin to recover.

Summing up: even in water rationing, you can hand water. A couple of low-level waterings twice a week can save a great deal in resources in the long run.

 

 

From the Image Gallery


Carolina cherry-laurel
Prunus caroliniana

Carolina cherry-laurel
Prunus caroliniana

Carolina cherry-laurel
Prunus caroliniana

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