Rose of Sharon leaf drop

quincypamSeptember 22, 2007

I have three rose of sharon that are very old. They are large (7 feet high). We transplanted them a few years ago and they were mostly doing fine. The past two years, two of them began to show leaves a little late. Once the leaves were in bloom, they appeared normal. All three bloomed flowers beautifully, but then the two that were late seemed a bit faded (while all the while still producing beautiful flowers). I went away this week and when I returned, to my dismay, the leaves had turned a bright yellow and dropped! I had fertilized them and been watering them well. The leaves also seem to have some black spots on them. No evidence of bugs though. Any advice? Help! I don't want to lose them!

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These shrubs do well without much care, so my first thought is that the fertilizer was unnecessary and maybe was too much for them; or perhaps it was an alkaline fetilizer that changed the soil ph beyond what they like. I'd get a soil sample from near the root ball of one or more of these shrubs and have it tested. (The conservation districts are holding plant sales this weekend, and doing soil tests, but not sure if there's an event like that near you, or if the testing is on Sunday or just Saturday. ) They like a PH of 5.8 - 6.2, according to the PW web site; they grow like weeds here in acidic soil.

Have they been getting a good soaking once a week, or just being "sprinkled" every day? Mine sometimes wilt a little in the heat, but I don't water them or feed them at all. You might check the soil nearby by digging down about 6 inches and seeing whether it's dry or wet.

I suppose the decline over a few years may mean that they're not happy in their new location - is it especially sunny, windy, dry there? Is the drainage good? Maybe too good? Are they mulched?

    Bookmark   September 22, 2007 at 9:40PM
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The most recent UMass landscape messages addresses this. Scroll up for the bad news. :(


    Bookmark   September 25, 2007 at 2:40PM
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Donna, is this what you mean?

Pests/Problems: Premature fall color of many deciduous plants, due to drought stress, is evident. The leaves on some trees are turning brown, and some trees are dropping leaves.

... or this?

Rose-of-Sharon caterpillar (aka hibiscus caterpillar, Anomis commoda) remains active on rose-of-sharon hibiscus. This introduced pest has the potential to completely defoliate this host plant when it occurs in large numbers. Where Japanese beetle tends to create a skeletonizing type of defoliation on this host plant, the rose-of-sharon moth caterpillar consumes leaves in their entirety.

I think it's most likely drought stress, maybe compounded with fertilizer that was not needed, but maybe not.

    Bookmark   September 25, 2007 at 5:43PM
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