Ortho Grass Be Gone is made to use in flower beds. Be sure to check the label.

I hand weed mine. Just crawl on in!

By hand, small hoe, knife, or a hand weeder/dandelion weeder.

https://www.amazon.com/True-Temper-1983800-Best-Weeder/dp/B00004S1ZK/ref=sr_1_5?s=lawn-garden&ie=UTF8&qid=1473159728&sr=1-5&keywords=dandelion+weeder

I think you are playing with fire if you try to do it chemically! What zone are you in and how old is the plant and how big? Can you take some photos? Have you mulched or used ground covers under your bushes? I have more than 40 hydrangeas and grass is not a problem because the root balls are solid enough to keep out grass. If it is really a bad problem, then I would dig up the plant, wash off the roots and pull the grass out from the bottom. Make sure to pull any roots under the root ball and then pop the plant back in the spot where you lifted it. Don't be afraid to dig up a hydrangea - especially for a few hours. Be careful not to cut too many roots but most hydrangeas are pretty shallow rooted and easy to dig. After you replant - be sure to water well and you might have to add some new soil, but be sure to mix it well with the old soil. Mulch the plant well. The mulch will not only keep the soil moist but prevent more grass or weeds from under your hydrangea. Do not add fertilizer at this time - you don't want to encourage new growth that will be killed by the first cold weather.

Smashing advice thank you.

If you do not extract the plant to extricate the grass and instead, you pull the grass from above, do it carefully and maybe wear some glasses as you do not want to poke an eye with the stems.