The other day I was reading a book published in 2012 entitled Decoding Gardening Advice, by Jeff Gillman and Meleah Maynard. It is subtitled The Science Behind the 100 Most Common Recommendations. Books that offer to give the scientific reasons for common gardening practice appeal to me.
The book covers such topics as sod, water, pest and disease control, trees, shrubs, vegetables, fruits and lawn care.
Each section contains discussions of “good advice,” “advice that’s debatable” and “advice that’s just wrong.”
The book is a fun read. Gillman is an Associate Professor in the Department of Horticultural Science at the University of Minnesota and co-author Maynard is a journalist and master gardener. They are good writers but be warned that the book is not geared for the scientist, and nary a footnote citing a source is to be found. There is no list of scientific journals supporting their conclusions and the “Selected Bibliography” is almost entirely popular books for layman.
Given the above, I read with interest the section on plant watering. They discussed the common advice to water in the morning and summed up the pluses and minuses. They say that watering in the morning is good advice for several reasons. The first plus when watering in the morning is that wind is minimal. This is in accord with my experience in photography that if you want to take a picture of a mirror smooth lake, you have to do it around sunrise. This is because wind causes ripples in the water and the wind is lowest at sunrise. They agree that morning (sunrise) watering involves the least problem with wind. And wind causes water to evaporate. Although they do not mention it, wind can also deform the water spray pattern so that sprinkler heads do not put the water exactly where you planned for it to go.
Next, they deal with the “water as magnifying glass” issue. One reason people give for watering before the sun is up is the fear that water on a leaf will act as a magnifying glass and cause the sunlight hitting the leaf to “burn” the leaf just like a magnifying glass can alight a sheet of paper. I’ve always had problems with this theory simply because we don’t get a bunch of burnt leaves when it rains during the day. Gillman and Maynard say that the magnifying effect can only burn plants with hairy leaves, such as ferns. They offer research by Gabor Horvath as the Eötvös University in Hungary as their scientific support. His complete article is available on the internet.
They do not discuss whether there is a best time to water using a drip system. All in all, they conclude that it is best to water in the morning when the winds are at a minimum and before the soil gets warm. They end with the warning that if your plants are wilting, it is better to water them immediately than to wait to water until the next morning to get “optimal” conditions.
In conclusion, although I do not think the book is full of science, the basic reasoning is well thought out and it is worth a read to find out what they think on other topics in their 224 page softback book.
This article originally appeared in the June, 2015, issue of The Rose Ette, the newsletter of the Houston Rose Society.
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