Concerning Aster Purple Dome: consider yourself lucky it blooms for you. Here in Denmark it blooms practically never and for nobody. I have thrown it out after 2 years of non-blooming.

In regards to Purple Dome, I find it strange your plant does that. Are you sure it's getting enough sun? That can certainly be a cause of floppiness. I'm also surprised this one doesn't bloom in Denmark. I wonder what's up with that? It blooms late for sure, but even here in MN it's still a glorious site in mid to late October. For some reason this year a few flowers are opening now.

Maybe it needs dividing. I tend to divide my every year since I sell a lot of divisions each spring. In fact, maybe dividing is the problem. The last couple of years, my Mum Clara Curtis was a horrible, floppy mess. This past spring I chopped the heck out of it and the resulting plant this fall is perfectly upright.

Purple Dome last year:

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Kevin

Never had a problem with nonblooming or volunteers too for that matter! I usually end up with more than I can handle in the small space it's planted in. I am thinking of finding a different place for it though, because it works great in spring and stays compact but hides my F&E hydrangea a little too much.

I prune my sedums and asters back by half in June. Otherwise they do grow long and lank and can flop.

Kevin ..... OMG that's a beauty. Thanks for the inspiration.
Buyorsell888.... did not prune in June.

I'll try posting a picture. Thanks all.

The third picture shows a new one planted this June the others last June.

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That's really odd. I've never seen this plant do that.

However....

It looks like this is a garden next to your house? If that's the case, I'm going to say not enough sun or not enough sun from all directions. I have another tall variety of aster which I planted about 3 feet out on the west side of my house. It gets lots of sun - both south and west, but it's leaning terribly away from the house. In fact most of the plant is on the ground (grrrrrrr). I'm moving it next year.

Kevin

"Autumn Joy" and some asters certainly can develop sprawl. Ways to counter this include growing them in maximum sun and well-drained soil with a light hand on the fertilizer, or as noted, trimming them back in spring to get shorter plants. "The Well-Tended Perennial Garden" is a book that has a lot of info on plants that benefit from this (and optimal times to do the pruning).

Rudbeckia triloba in my garden benefited from a trim in late spring, flowering at a little more than half the size of an unpruned clump. I need to remember to cut back Rudbeckia "Herbstonne" next spring. It's invaluable for its long blooming season, but without pruning and staking it's all over the place.

These are part of my new curb appeal garden that I put in last year. The exposure is from the East from 7 am 'til 2 pm. My SE exposure of the Sedums is better than the SW. The Sedum that gets no sun is only good for 2 years and I then pull everything and start a smaller piece which in 2 years is perfect then downhill from there. So easy to divide Sedum so that's the way it will go.

These Asters (first time using them for me) will get the prunninng of their lives next year as soon as they reach the size of a volleyball hoping they bouce back to be more like Kevins (short and bushy. If that fails time to move then to a full sun south exposure. BTW Kevin is your Aster in full sun ? What height is it and width? Hard to tell without a reference for size comparison. Thanks again all. Happy gardening.

Anyone think I should prune now (think it's too late)Maybe tie and stake this year. Maybe buy some potted mums to sit in the middle this year, probably yellow.

Rory

Yes, my aster is in full sun. Since I divide mine every year, that particular plant is probably 18 inches tall and maybe 2 feet across.

Kevin

Think I figured it out. This plant only flowers on new growth wood. Not having cut back last years plants to the ground the new growth just added itself to the old which doesn't produce new greenery or flowers.
If I had the blooms are great right now but the old woody growth from last year couldn't support the new since the plant is now top heavy.

Question .... should I have cut it right back to the ground in late fall after the blooms die or wait 'til spring before it starts to grown. I think that's called keeping the plants "under control" (lol). Thanks folks for the help. This my first year with this plant.