Can you tell us more about the conditions they're growing in? Are they new or mature? In shade or sun? Have you fertilized a lot, a little, not at all? Do they completely splay open/flowers lie on the ground, or just droop mildly?

Without more info, I would guess 1) still maturing so stems are not yet as strong as a mature hydrangea 2) doesn't get as much sun as it would like or 3) grew too fast at some point in the spring/early summer this year.

While figuring out the larger problem, you could prop it up with wire fencing or stakes/thread, both of which should be pretty invisible if you let the foliage drape over and through.

Here's an old thread on the topic.

http://forums.gardenweb.com/discussions/2053613/endless-summer-hydrangeas-flopping-over

Thank you so much lalala. I believe you hit on all of those points. Yes, it is in the shade most of the day with filter sun. It was planted last year from a 2gal pot. Though I did not fertilize it, it grew alot in the spring. When I bought it the plant was in bloom and the stems were very upright. It was displayed in a shaded area of the nursery. Will the stems get stronger as the plant becomes more mature? Is there something I can give it to help it be more upright like certain fertilizer? I can provide support for it but I hope that is not something permanent.

I'd think that if it's only in its 2nd year and you like the location you chose for it, you should give it some time and it will strengthen. Generally ES are not the droopiest of hydrangeas. Since one don't usually prune them much year to year, the old wood will be stronger/tougher and will hold up the new growth. This year it just didn't have much tough old wood yet.

If you find over time that it's not blooming well (even after mild winters) and is still floppy, you can consider moving it. ES can tolerate more sun in your zone--morning sun and afternoon shade is a good combo.

I think overfertilizing is worse than underfertilizing. I don't put anything on mine, which are 10 years old and well established. If you feel like the soil could use help, compost and mulch are a good idea.

For this year a peony cage would be great support it if it's still small enough, or stakes with twine or rubber-covered wire. Giving it support will also help "lock" the branches in an upright position while they mature/toughen up so they're more likely to stay that way.

This is the wire I've used to stake my Annabelle hydrangeas (which are naturally floppy):

http://www.amazon.com/gp/product/B00HVVZ6TQ/ref=pd_lpo_sbs_dp_ss_1?pf_rd_p=1944687442&pf_rd_s=lpo-top-stripe-1&pf_rd_t=201&pf_rd_i=B00Z7YH7GO&pf_rd_m=ATVPDKIKX0DER&pf_rd_r=0FE3F6T1VG4YF7RMGM5Q

I agree with the sun thing. Otherwise, it might just take some time. My strongest-stemmed ES I bought 6 years ago now. First one is just hitting about 4x4'