Asters don't come in as many forms and colors as mums. The blooms come in large and small. Purple, magenta, blue, pink, and white are just about it for color. But they have their strong points, too. Asters are generally hardy through zone 4, with some even surviving zone 3 winters just fine. Mums are supposed to be hardy through zone 5, but that can be rather iffy.
Mums come in such great colors and forms. There are elebenty-lebben shades of orange, as well as red, yellow, pink, purple, and white. There are cushion, spider, football, daisy, quill, spoon, and pompom mums. There are garden mums (perennials) and florist mums (annuals). In short, there probably is a mum that can please just about anyone.
And then there are the asters. Another fall bloomer (most of them, anyway) that provides a bright splash of color when much of the garden is winding down for the season and half of us are either depressed because it's over while the other half is welcoming the break.
For a nicely-shaped mum in the fall that has the maximum number of blooms, continual pinching back of the growth tips until the 4th of July is recommended, while asters don't really need this. They are just naturally beautiful all on their own. You can pinch them back a couple of times if you want to though, for a bushier plant come fall.
I personally have this love affair going on with asters right now, because I've not had the best of luck with mums surviving our winters here. I have yet to lose a single aster. To be fair, once I started following the recommendation of providing good drainage for my mums and not cutting them back in the fall, I haven't lost any of those either. But you'll hear me give a whoop of joy in the spring when I see they've made it through another winter. You just never know.
It's unbelievable how fast the asters grow. I planted 'Wood's Blue' last year as a quart-sized plant. It now takes up a space of nearly three square feet, is completely covered in blooms, and has gobbled up the 'Edith Wharton' iris. I'll move the iris next spring.
The daisy mums, like 'Clara Curtis,' 'Bolero' (shown at left), and 'Rhumba,' are super reliable for me and I highly recommend them if you have trouble keeping mums around. But in my quest to make gardening easier, I'm focusing on asters for adding some fall color this year.
In the last couple of years, I've searched for white asters and for some reason couldn't find any in our local garden centers. I found some alpines, which bloom in late spring, but I wanted some white fall asters. Yesterday I finally found some, at Lowe's. They're New York Asters (Symphyotrichum novi-belgii), hardy to zone 3, and I bought two of them at $6.98 each for a large pot. These are also called Michaelmas Daisies, particularly in Great Britain, because they usually are in bloom around the Feast of St. Michael holy day, observed on September 29th.
A word about mums and their name: Once belonging to the Chrysanthemum genus, they're now classified as Dendranthemums. Oh wait. I think I heard they're Chrysanthemums again. Or not. Those crazy taxonomists can't make up their minds and I can't keep up with them. We can still call them mums, though. And those Asters? Their genus is Symphyotrichum.
Mums or asters? Asters or mums? Just plant some.