There is no conceivable reason to stop deadheading in your climate. The advice you heard was based on the (probably mistaken) belief that setting fruit helps roses prepare for winter dormancy in cold climates.

December sounds early for pruning. Your roses should be blooming near their best at this time. If it gets cold enough to slow growth in midwinter, that would be a better time. If you state your location, someone could give local advice.

-- December sounds early for pruning.

*** No. Not really.
In Southern California, you can usefully prune (IF you are going to prune at all) any time between today and, say, the end of February.

I am assuming, of course, that the O.P. was asking about modern roses.
If the question referred to Old Roses, the answer might vary with the SORT of Old Roses involved.

Jeri

michaelg was suggesting I mention my zone which is 9 of Southern California as far as I can figure. It is in the San Gabriel Valley inland. And someone else mentioned that that area is probably sunset zone 18 or 19. I've probably mentioned this before that I have 63 bushes and most of them are on the old side.

I prune according to what I think the rainy season is going to do--this to avoid as much rust as possible. You either have to live with rusty roses on the old foliage in Dec-Jan or with rusty roses in Mar-Apr on the new foliage. I'd rather have the rust on the old growth instead of the new growth, so the past few years Ive been waiting later and later.

I keep deadheading because I want as many flowers as I can get. I've read if you want to induce a little dormancy in So Cal, cutting way back on the water slows them down more than not deadheading does. I've tried it, and it seems to be true, at least for my yard.

I agree with Jeri & Hoov. Basically, I deadhead until mid-November to get blooms before I do my major pruning for the year which goes from Christmas to Valentine's Day. It takes me awhile to prune everyone b/c I have ~300 roses and a more than full time job. Normal folks in So Cal would do their major pruning in mid-January over the course of a day or a week or the month. Any deadheading you do much after mid November will produce growth or blooms that will be pruned off in the January big prune, perhaps before they actually bloom. I do dance around the ones that are blooming in January during the big prune.

Michael G is very knowledgeable about roses and is rock solid in pretty much every regard with his advice, but he doesn't understand the nuances of rose growing and pruning in So Calif. Monrovia, I knew where you were based on your name. I spent the first 31 years of my life in Pasadena, until I moved up the road to Santa Barbara in 1987. You & I & Jeri & Hoov are all pretty much in the same area in terms of winter pruning.

Susan

"fallen petals are food for the insects and make them healthy".

That's a new one for me. Which insects? and is it the insects that are made healthy, or the roses? Please explain.

Fallen petals do contribute to soil organic matter if left to decompose on their own, or added to compost. I don't know that it would be a noticeable contribution. I've always tried to pick them up to avoid culturing botrytis fungus. Topdressing with compost or mulching with fallen leaves would do just as much and probably more, than leaving the fallen petals.

Mid December is not too early for pruning in SoCal. In fact I've heard of widely-respected rosarians in Portland starting their pruning in mid December. (Up here we're limited by weather and available daylight more than you are, so people prune when they can get out in the garden.) In the SF area (Sunset zone 16 in my case) I pruned in mid January. Yes, some of your roses will still be blooming. Cut those roses for the house first, then go ahead and prune. You won't be able to catch them at a time when none of them are blooming.

I'm also in SoCal, and I still deadhead this time of year -- we don't have a real dormancy period here because our climate is mild.

I prune what needs pruning in January. With once-bloomers I prune after they finish flowering, usually in the summer.

Thanks to a number of folks who gave me advice re deadheading and pruning at this time of year. I did dead heading today and will hold off on winter pruning until Dec. or Jan.

reg pnw7 questioned that fallen petals feed the insects making them healthier to attack the roses. I read that somewhere but I'll be happy if you think it is false.

I honestly do think that's false.

Some people find it MESSY. It doesn't bother me.

Jeri

The only bugs I notice eating petals on the ground are earwigs and roly-polys. Here, they don't climb up to eat fresh flowers. They stick to the mulch.

Fallen petals might contain live thrips or botrytis fungus, but that doesn't necessarily mean that gathering all the petals would control these pests.