This is a quote directly from Tracy DiSabato-Aust's book: "Do not prune for the winter."

They are short-lived enough as it is; cutting them down only decreases the chances of winter survival further.

If you decide you must, at least wait until you have had several hard (killing) frosts or you risk the plant putting on new growth using energy reserves intended for Spring.

The Coreopsis at the front is C. grandiflora 'Early Sunrise' and 'Sunray' and C. lanceolata 'Sterntaler'. The last Coreopsis planted in this isolated bed was eight years before the picture was taken.

At the same time, all perennials (including the Coreopsis), were cut down to the ground, every year, by late September or early October (before any noticeable frost).

Some reseeding did occur, but the seedlings which I noticed were weeded out.

Perhaps what the author's says is appropriate elsewhere.

I will also add that Tracy Di-Sabato-Aust is but one person and there are probably some or even many who disagree with her. To combat flopping and sprawling, she does recommend cutting Coreopsis grandiflora back in summer if it starts to look ugly. She recommends cutting down to basal foliage in late summer/early fall to stimulate bud growth for next season. So, she does suggest a way to avoid the floppiness by cutting back early while still encouraging some vigor for winter survival.

Thanks for the qualification, Mistacott.
It's location, location, location (sometimes even within the same garden).

Wish that was my property. Just planted and maintained the perennial beds.

The reasons I always cut standing perennials down in fall is (i) neatness, being able to monitor (and deal with) what's going on with the perennials at ground level, being able to weed effectively, and (ii) next spring, being able to see spring bulbs (especially the earlier smaller things like crocuses) and not wanting to walk on beds when they're wet (including from snow melt). In the latter case, don't want to damage the later spring bulb or low spring perennials.

Spend a lot of time staking plants and always happy that don't have to stake things like Coreopsis an Gaillardia (which have very long potential bloom times).

I do spend a lot more time deadheading, including Coreopsis and Gaillardia to keep the blooming going.

Must be location.

My kind of perennial bed requires sunny locations and all my experience is with this region.

Cutting back in fall is sort of out of vogue in the gardening world right now. But I think if it were really catastrophic for perennials, it wouldn't have survived for so long as a practice. There are certainly advantages to it, especially when it comes to preventing disease/fungus/rodents. I think it is just a matter of preference. DiSabato-Aust's recommendation to cut back heavy flowering perennials in late summer but not for winter comes from the work of Hansen and Stahl in their 1993 book Perennials and Their Garden Habitats. I do not know if they tested their theory or if it is just a theory with no data to support it.

DiSabato-Aust does caution that if you do cut back, to only cut back within 2-3" inches of the ground because some of the basal buds for next season do develop slightly above or at ground level. Not sure if this applies to Coreopsis or not.

I also grow bulbs in my perennials beds so I usually cut back in very early Spring and often before new growth comes from the perennials -- which is not exactly what is recommended -- but it hasn't caused any problems so far.

Best of luck,
Scott

Agree, Scott, it is a matter of "preference", or, perhaps should be (sure you would agree) of "informed preference".

Must say I'm a bit sensitive to anything approaching top-down pronouncements in gardening, "abhominable magenta" (viz. Gertrude Jekyll) moments!

Love the early spring bulbs. It's unfortunate that our voles/meadow mice feel the same way!

Charlie.