Re other perennials and deadheading.

In addition to tidiness and encouraging more bloom, deadheading prevents/limits reseeding around perennials like musk mallow and rose campion.
Deadheading, and gradually cutting back after blooming, also enhances air flow around summer perennials like garden phlox and false sunflower.

How late in the year should I continue to deadhead roses? It's still in the 80's here during the day, but starting to cool off at night.

I continue deadheading as long as my roses are still growing and producing blooms. In my zone, I can even have blooms into Nov. and Dec. Less sunlight/shorter days and freezing temps will stop growth and freeze any buds.

I live in the mountains of northern California. I'll probably have one more full flush of roses, but I stop dead heading around the first of October because I want the roses to set seed and harden off for winter. I'll still get blooms until the first frost, which may not arrive until mid-November.

In my climate, the day temps can go from the low 90s down to the 50s within a couple of days and night temps drop just as dramatically. I don't want to encourage new growth going into winter. Besides, the hips on some roses are simply beautiful in the winter garden.

Smiles,
Lyn

Thanks! I am taking care of an elderly friend's garden and she has some very old roses, some of which were brought over from Germany. I don't want to do anything that might be detrimental to them.

How very kind of you.

Blessings and good luck with helping your friend.

Smiles,
Lyn

Thanks, and thank you for the acorns!