Experts tackle readers’ garden questions.
Q: A couple of seasons ago, Garden Detective ran an article about dogwood trees having either a manganese or iron deficiency. My tree fits the description of manganese deficiency. I found manganese online, but there are no instructions on how to apply it. Can you help? The tree is looking pretty sad!
Joan Willard, Sacramento
Bee garden writer Debbie Arrington: Your memory is right. In December 2015, Garden Detective tackled problem dogwoods and possible mineral deficiencies including manganese.
Harry Andris, a retired farm adviser in Fresno County, noted that lack of iron isn’t the only mineral deficiency that can lead to yellowed leaves.
“There are a number of things that can cause yellowing and inter-veinal chlorosis,” Andris said. “Iron deficiency is certainly one of the deficiencies that causes inter-veinal chlorosis; however, manganese deficiency is also one element to consider.”
Look at the leaves, he said. That helps in diagnosis.
“Both can be caused by excess soil moisture but iron deficiency has a very fine network of green veins with areas of inter-veinal yellowing along the major and minor veins,” he said. “(In this case), the major wide green veins are the symptoms of manganese and not iron deficiency.”
Manganese sulfate, available at nurseries, is the most common form of this fertilizer. Apply according to package directions; usually 1/3 cup dissolved in 5 gallons water, to cover 100 square feet. One application per year is usually enough.
However, excess manganese can cause problems, too. Before adding this trace mineral to your soil, do a soil test. Kits are available at nurseries and garden centers.
According to UC master gardener Annie Kempees, yellow or chlorotic leaves on dogwoods also may be a sign of iron deficiency.
This is much more common in the Sacramento area, especially in clay soils. Iron deficiency is usually caused by alkaline soils or those that are very wet, or have drainage problems.
In a healthy plant, most of the leaves are green. In leaves with iron deficiency, veins are green, and the areas between the veins of young leaves have changed to light green or yellow. As the chlorosis increases, the leaves may become smaller, taking on a whitish cast and have dead margins and tips. Twigs die back and defoliate as the deficiency increases.
Iron deficiency can be corrected by acidifying the soil or using iron fertilizers, according to package directions.
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