What's wrong with my dahlia?

TruNorth7(8b (SF Bay Area))August 19, 2011

I picked up some small dahlias from OSH a few months ago. They were in 6" pots and about 8" tall. I potted them up and put them on my front porch steps. For quite awhile all three bloomed like crazy.

Within the last 3 days, one has started to wilt and shrivel up. The leaves first turned lighter green (but not from powdery mildew or anything) and now are yellowing. There are no bugs on it and I see no cause for the rapid dying. The others from the same purchase look fine, as do my Dinner plate Dahlias that are in the garden beds. My dahlias usually bloom through October then die for the winter, so this one seems to be going abnormally early.

The dahlia is in high quality potting mix and has good drainage. I keep it well watered (but never soggy). It gets about 6 hours of sun each day.

Does anyone have an idea as to why this plant is randomly dying? I moved it away from my others, just in case. I save the tubers each year and re-plant them in the ground. If this one dies, is it worth saving the tuber? Is it likely to be diseased?

Any advice would be appreciated, I really would like to save this plant.


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I cant give solid advice, but I had a similar thing happen last year. I picked up two Dahlias in baskets, they were small collerette types. both got sick and slowly died. They started with leaves yellowing , then curling and drying up. One of them was completely dead by fall and I just tossed it, the other managed to hang on, but I was not able to get the tuber to eye up this spring (and I was successful with over 100 other tubers). While I have had insect damage and even a little fungus on my orchid dahlias, I have never had anything like this happen before. My assumption was that being a relatively new dahlia type they were susceptible to something I havent seen before. (and hope I dont see again!)

    Bookmark   August 20, 2011 at 9:03AM
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Both of you are growing dahlias in pots. For some reason, dahlias grown in pots can get root rot and die. Most often the cause is over watering, but once they get it they generally die even if they are re-potted. It is a fungus disease. If you used old potting soil, it can be contaminated with fungus spores. Root rot affects may plants grown in pots and commercial nurseries use fungicide drenches to prevent it on some plant varieties that are prone to it.

    Bookmark   August 20, 2011 at 10:58AM
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Its also possible that the tuber simply rotted due to too much moisture sitting deep in the soil. I had a larger dahlia variety die after a week of everyday occasional rain, and when I dug it up, the bottom 2/3 of the tuber were rotted to slime!

    Bookmark   August 20, 2011 at 12:42PM
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TruNorth7(8b (SF Bay Area))

Thanks everyone! The tuber rotting makes sense. Bummer, it was such a beautiful plant :(
Thanks again for the help and ideas

    Bookmark   August 22, 2011 at 4:48PM
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