I don't know too much about mums in general. What I do know is that most perennials get ratty when they are in the ground in one spot for several years. Most plants will die off where the oldest growth is --in the center. Before you buy new plants try rejuvinating them by digging them up and dividing them and replanting them

vieja:
Do you know what kind you have? My Country Girl mums have spread madly in my sandy soil, which has allowed me to move some & make whole new areas of them, and give a lot away. I cut & pinch them back often until mid August, to keep them shorter & bushier. Compost in the spring and a few alfalfa pellets is all the feeding they get.

These pink areas (taken in 2006) started as 3 little 4" pots:
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I agree with oilpainter . . . give yours another chance. Maybe mix some compost into your soil when you replant them.

I used to grow them commercially, but haven't done so in about two years. Yes, they can be rejuvenated. Like with so many other perennials, the crown eventually becomes woody and often the stems coming from them will splay out revealing the dead and woody material in the center of the clump.

If you have a non-patented variety, you can easily start cuttings from them. If you don't want to bother with that, you can lay one branch of them down and French layer it with soil over it where it should easily root along the stem. Next spring, just sever it from the mother plant and plant it elsewhere.

If you are lucky enough to have had a plant who has developed a multi-stemmed clump, with roots you can sever and divide, just do it.

I have found the newer varieties are bred to have multiple, smaller blooms. They cover the foliage like a carpet and are lovely, but they also tend to splay out when they bloom just from the weight of the blooms and can look unthrifty. Proper pinching can help them have stem strong enough to hold them in place.

The most important thing in overwintering a mum is to make sure its roots don't rot. That's why sandy soil is sometimes an advantage. But, I overwinter mine in clay soil, usually without ammending it. I tend to plant mine on a slope so that when the soil is saturated, it eventually drains downward and the roots of the mums aren't sitting in a pool at the bottom of it all.

I am in SE Michigan, Zone 5, and have always been told not to pinch or prune back mums after July 4. Do you think I would be as successful as treelover, who is in (tropical) Zone 8b, if I kept pinching up to mid-August? I hope so, because even having pinched July 4, my mums are still straggly and not as bushy as I had hoped this year.

patann: Mine bloom in October, and I stop pinching them about 6-8 weeks before that. Do you know when yours bloom? If you pinched them in mid-Aug would they still have time to make buds & bloom before frost hits?

Are yours in full sun? I notice that mine that are in part shade tend to reach for the light and get lankier than the ones that are in sun most of the day.

Tracy DiSabato-Aust, who wrote the book on pruning perennials, says that mums and pruning go hand in hand . . . to delay blooming & control height. She recommends starting when they're about 6" high & stopping in mid-July for zones colder than 6, because they need several weeks to set bud.

treelover, since you (and others) have referred to DiSabato-Aust's book before, I now feel assured it is one of the best and will go back to it shortly. I need to understand the difference between pruning and pinching and I think she did that. Instead of pinching the buds off mine, I've been cutting the whole plant back by half. That may be my problem. My mums get more sun than shade but I cannot say "full sun." Thank you for your response and it's good to see you are on more than the Trees Forum. Pat.

That might be why yours are still so tall, patann.

I said 'pinch' but I do cut mine back hard during the late spring/early summer. I've taken as much as 1/2 off the odd stalk, though I try to remember to do it regularly so there's less to remove. I don't have any rules I follow in deciding when to prune them ... when the mood strikes, or I notice they're getting big.