I deadhead virtually all periennials and annuals. I sever at the first set of leaves below the flower. Hopefully, others that are more knowledgeable will weigh in. Be careful not to cut off buds that haven't bloomed yet.

I only deadhead a couple of plants in my garden. Amaranthus and Dianthus. The rest seem to take care of themselves just fine without any help from me. I will also cut the spent stems off my Jewels of Opar when they have all become seeds to keep them from over powering the area with more plants after blooming.
Other than Chrysanthemums and standard Petunias, not too many flowers require deadheading on a regular basis.

I have been deadheading my coreopsis and scabiosa, ever since posting a similar question earlier this spring. It has rewarded me with blooms that just won't stop. I literally can hardly keep up. In fact, I'm forcing myself to only go out there and deadhead once a week; otherwise, I would be out there constantly.

I deadheaded our blackeyed susans and coneflowers last year with limited success. I've been deadheading our coreopsis 'nana' this year with great success. I always deadhead our roses with great success as well.

So, in a nutshell, it seems to be really hit or miss for us.

Vroomp brings up a point I'm curious about - our dianthus bloomed light pink in spring, and has just begun to re-bloom - some on old buds, it looks like? Is this possible?

I never removed the dead heads, I've just flipped the dried buds over (back into the plant) like a water pitcher to dump out the seeds.

satellitehead -- Good question (I don't know the answer to it), but I have another one: when you deadhead...and let's say it's a platycodon (balloon flower)...do you just pluck out the spent bloom or do you remove the whole bud that the bloom came out of? I have tried it both ways and it looks weird either way. Someone suggested to me earlier this spring that it depends on the flower as to how you would deadhead (ie: pinching off just the bloom or cutting the whole flower stalk), but I forgot to ask about this kind of bloom as well.

with my gardenias, i pinch off the bloom, this may not be correct, i really have no idea. with the heuchera 'silver scrolls' and coreopsis 'nana' (i have several), i just bunch together the shoots and cut them off, although with the heucheras, the only way to make it look "nice" is if you pluck every individual shoot out, which is possible but very tedious.

with dianthus, it seems like you could just pluck the flower out. but, like i said, very weird, first bloom on the one i just transplanted to my mailbox was pink, the bloom browned/dried/seeded, then i swear a new dark pink bloom pushed the old one out, then shedded the dried portion of the previous bloom. (i could be nuts, though)

I can't say I have ever seen that happen before so I really couldn't say how that's possible other than another bud must have formed below the first and just wasn't visible before.

By the way, I called around for Lady In Red and no luck. Did you find one or have you called Hastings?

I didn't call ... I'm just going to pay a little extra and go to Habershams tomorrow. Habershams is 5 mins away, so I'll save the $$$ in gas.

Blazepepper,
Regarding your annual salvias, they are probably Salvia splendens. They will benefit from fertilization and deadheading to maximize blooming.

Thanks for all of the replies, I guess my only question now is exactly how you dead head? I mean, do I take a pair of scissoars and cut any remaining bloom off of the plant as it begins to fade or what? A detailed explanation of the steps involved would be helpful. thanks again

This link should help. Hit related links if you want to see more videos related to pruning.

Youtube has become a phenomenal source for videos related to gardening.

Here is a link that might be useful: Deadheading Roses and Perennial Plants (Youtube)

After a Gardenia bloom has wilted, how far back on the stem do I cut? This is the first Gardenias I have had. Please answer.....