Someone asked about my centaurea montana (aka perennial cornflower, mountain cornflower, bachelor’s button, montane knapweed or mountain bluet), surprised it was so large. I’ll note that this one is at the top end of its size range — it typically grows 1-2′ high, and this one (first photo) is a full 2 feet, I think. It must be very happy there (light deciduous shade, west-facing).
The second photo is one from my back garden — as you can see, this perennial has gotten big enough that it’s flopping over, with an unattractive center — that will happen after 3-4 years, typically. It may flop more if the soil is too moist or it’s too shady — it’s happiest with sandy soil and plenty of sun, in theory, though it’s pretty tolerant of my thick clay + 10 years of leaf mold + mulch soil.
Now, there are two basic approaches to dealing with flopping from the center, I think — you can plant thickly enough that various other plants will hold it up, essentially, or when it gets to this stage (or is about to), you can divide it, making smaller plants. (You can also plant in pots, low enough so the pot structure holds them up, but then you’re needing to be diligent about watering, which I am not.)
You can divide in spring or fall; in theory, it’d be better for me to divide now, when I have a better chance of remembering to do it, but the problem is that I still have a fair number of recently bought plants to get in the ground, which is more urgent, since they’re more likely to survive if I do, esp. given my haphazard watering.
So priorities — get new plants in the ground, don’t buy any more new plants, then hopefully divide this one. Of course, there are still all the vines to tie up, etc., the roses I didn’t get to yet, the seeds I never started, the tomatoes and dahlia and glads to get going after Memorial Day, etc. and so on…we might just have to live with a little floppiness this year.
Note that centaurea montana will also rebloom in fall if cut back after first blooming period. I rarely remember to do that! The blue-purple is the straight species (native to Europe), the purple and white cultivar is named “Amethyst in Snow.” That one is new in my garden last year, so still quite small. Other cultivars worth checking out (may require some hunting to find) include: Alba (white), Amethyst Dream (violet), Blue (less violet), Carnea (pink), Parham (large lavender-blue), Violetta (violet-blue).
