Maybe the tuber actually got "Cooked" in its container? I would dig down and check the tuber itself and the condition of roots coming from it. Can you do this without pulling it up? How is the drainage from the pot? Its OK if the dahlia wilts a bit in the afternoon as long as it perks up again in the night time. I wonder if you over-watered and turned it into dahlia stew?

There seems to be a plethora of these postings lately about watering (whether lack of or overwatering) and because I also used to 'think' I knew what dahlia experts said about watering (and was wrong) I share this info.

It is well known you needn't water tubers before they sprout. Many then think dahlias therefore don't need a lot of watering thereafter but it is NOT TRUE. Swan Island's catalog (and from other growers sites I've searched) say: "After dahlias are established, a deep watering 2-3 times a week for at least 30 minutes with a sprinkler, more required during warmer dryer weather. Hotter climates will need to water more often as conditions require. Proper watering promotes proper blooming. Hand watering is not enough.".

I too underwatered my dahlias for years after they bloomed. Turns out I need to water ALMOST DAILY here in S.F. and it is rarely sunny in the summer. Earlier this week, I noticed a brand new dahlias with a nice bud had turned downward. The ground appeared wet around it (I had watered 2 days before) but I watered it anyway and it perked right back up! So now I water virtually daily, unless they haven't any blooms open yet.

I suspect your 1 1/2 gals., 3x a week is way too little in that hot of weather. As S I says, 3x a week is OK for regular climates and if using a sprinkler but as they say, HAND WATERING 2-3x a week is NOT ENOUGH. Those big colorful blooms need lots of water to hold themselves up - just make sure you don't continue watering after the plant is done or it will then set the stage for rotting over the winter.

Thank you both! liza, I've checked the top of the tuber by pushing back the soil and it seems ok (no soft spots or obvious damage) I don't honestly think I can dig it up without killing the plant outright. I am certain the problem is not overwatering, drainage is very good and the sweet potato vine in the same container is VERY healthy (they are really good indicators of moisture in my exp). David, what do you mean by "after the plant is done"? This tuber was brought out to sprout quite early and was blooming by early may...is it possible that this is just how long it lasts? 2 months of bloom is great for just about any kind of plant. I will try giving it more water for a week before I get drastic and just cut it back by half (which works with petunias LOL might with dahlias too).

Ziya

ziyakr: Some dahlias will only bloom for a couple of months so it is possible your dahlia will SOON be done. But by 'done', I mean no new buds, leaves yellowing and drooping, looking very fatigued, etc. Your original note said you had BUDS still, so that does not sound like it is done (though it may be NEAR to be done).

I suspect lack of water caused your problems but definitely you may only have a few weeks to go to the end of its life span anyway. I also know that growing other plants within the same containers as a dahlia ALSO tends to cause a lack of proper water in the dahlia, combined with your saying it drains well makes me almost positive lack of water is your problem.

I would NOT cut it back! I have never cut mine back nor have I ever read that doing so was beneficial in any manner. In fact, after the plant is truly done, you should let it sit for weeks because just like tulips and daffy's, this is when the plants get energy to bloom next year. Maybe others can chime in if they have done so but the only pruning I do is when you pinch the first bud to promote more growth and bushier dahlias. One of the problems with cutting a large stem back is that they are hollow and water could conceivably get in the stem and ride down all the way to the tuber and start a rotting process. Perhaps if you are careful when watering that would not be an issue but I don't cut mine back after flowering - I just let nature takes its course and get renewed for the next year.

Good luck.

I wanted to thank you again, David. I think you were right about watering, generally. The plant survived 3 more weeks of blistering summer with minimal damage at higher watering levels. It's only just this week opened a new flower, and I wanted to try and put up a picture (the flower is smaller than earlier, about 2.5 inches across but still lovely and I'm thrilled to see it). I am going to try again to overwinter the tuber, but next year it will be in it's own moveable container. That way I can keep a better eye on moisture levels, and slide it into part shade if need be during heatwaves.