Does the nest you see look like it's made from a ball of gray paper? If so it's probably a hornet nest as yellow jackets live in the ground. Anyway, if they are above ground you can try a product call Decon which is specifically for wasps and hornets. It will shoot a stream of insecticide about 20'. I'd do it in the very late afternoon when all of the wasps/hornets are back in the hive. I'm not generally a proponent of insecticides but if it's a white faced hornet nest you don't want to get close to it and you need to get rid of it!!!

hmmm

This is a tough one. YJ stings hurt. Are you sure they are Yellow Jackets and not some other type of wasps? Yellow Jackets prefer to nest in the ground, but it's not unheard of for them to be in something else. If you can't get a good view of the nest, it will be hard to figure out the best way to get rid of it.

If you're trimming with electric, you might want to stop and switch to trimming it by hand to avoid making them upset. If possible, I would leave them alone, they won't make it through the winter, and then in the spring, you can just pull the old nest out.

If you really want to get it out, You're going to have to put on some protection and get into the hedge. You might consider calling an exterminator if the nest is really huge. Not worth getting stung repeatedly.

I went back at dark and shined a flashlight on the nest and a fewyellowjackets came out so I let them calm down fo about a half hour then it was really dark. I could see part of the nest but not the entry or exit holes and decided to give it a good shot of spray a good long shot and sure enough it got them which I am very thankful for. Thanks for the help.