Close up.

Are you talking about Shasta daisies? Depending on cultivar they can reach anywhere from 18" to nearly 6'.

You can keep taller growing forms shorter by pinching back to around 6" in early May. It looks like yours are setting flower buds now so too late to pinch/cut back for this season.

Hi! These aren't Shasta. At least I don't think so. They don't look like the other Shastas I have. But maybe?

Here is a picture from last year.

Those look more like some kind of helianthus rather than a daisy. Not sure about pinching those, if that's what they are, but I believe you can.

I think you need a clear ID on what you have before you cut back anything, though.

Dee

The plants in your first two pictures don't look the same as the yellow ones in your last picture. The foliage appears quite different. The first plants do look like Shastas.

Hi Flora. Thanks. Maybe I have my pictures mixed up? I'll watch and check back.

If they are Shasta, I still can't pinch them now because some have set buds, right? When deadheading, how low should I trim them?

Thanks!

If you pinch them now, you'll diminish the number of blooms you'll have to enjoy this season.

Deadheading Shasta daisies (as with most perennials in my experience), all you need do is snap off the spent blooms at the base of the flower. There's no need to cut the stems.

Personally, I leave the spent flowers on the stems so I can harvest the abundant seeds at season's end. These are easily grown from seed via winter sowing which spells more free plants & blooms for my garden in following years.