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michaelg_gw

Magnesium deficiency & foliar Epsom Salt

michaelg
13 years ago

Last year, for the first time, a few of my roses showed symptoms of Mg deficiency. See the link for its distinctive pattern. It appears first on the lowest leaves and moves upward. This means that the rose is robbing Mg from its least productive leaves and using it to build chlorophyll in the new growth.

I threw a handful of epsom salt at each plant and watered it in. Two weeks later, the symptoms were still progressing on the worst-affected plant, William Shakespeare 2000. I gave him another 2 ounces. A week or so later, he began showing apparent symptoms of a different deficiency, manganese, which affects the new leaves. I wondered if the dose of magnesium had somehow reduced Mn uptake from the soil.

Reading around, I saw that Mg deficiency in field crops is treated by foliar application of epsom salt. One source said that most plants can handle up to 2 oz. (4 TB) per gallon of water. Cannabis growers recommended a much more dilute spray. So I cut the maximum dose in half and sprayed parts of several plants with a 2 TB/gal solution, with no ill effects.

This spring, Willie showed a few more Mg "Christmas tree" patterns. Since I spray most of the roses with Bayer, I added 2 TB/gal to the spray, which worked fine.

A couple of months later, I repeated the treatment as a preventative measure. This time, probably because of extreme heat, a few roses suffered leaf burn, which developed very slowly but eventually yellowed about half the leaf surface. The affected roses were Marie Pavie (should have seen that coming), The Fairy, and Clair Matin. So 2 TB is too much in hot weather.

Just thought I'd share the experience.

Here is a link that might be useful: Mg def. on rose leaf

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