here are my thinkings - taken from the plant types do well in my garden..

- Hydrangea Annabelle - size ok, reliable bloomer yr after yr, white, can take a lot of sun and not wilting in summer, zone 5 - no problem at all, availability - widely available..only misfit - flowerheads will flop after a rainstorm - wide

- Hydrangea "Incrediball" - this is a new release, so you need to seek these guys out, and they can be pricey...BUT..this plant is everything like Annabelle, except the flowerball is larger and the stems are stronger - so the bloomheads dont flop like the Annabelles...this is the second season I have IB..the flower bud cluster is already 2 inches across and they are not even close to open (June is the blooming time)...I am replacing all my annabelles with IB this yr...size - it is a 4-5 footer..

- Hydrangea Limelight - popular - so easy to find, this is a reliable blooming - lime green, whitish bloom - big bloom heads - could flop though - sun, zone will work for you...not wilts under hot summer sun..HOWEVER - Limelight is tall, likely will not fit the size requirement..

-Hydrangea Little Lime - this is a new release, could be difficult to find in your local mkts - it is supposed to be everything like limelight, except smaller - maybe 3-5 feet tall..I have not tried this one out in my gardens..

- Hydrangea blushing bride - in my hands, a very reliable bloomer and a heavy blooming one as well...i like the white pinkish blush (or bluish blush, depends on pH of the soil) - it tends to get sprawly - will wilt under hot sun, so afternoon sun is not a good idea for BB - it could be difficult to get this plant in some local mkts - zone will work for you...sizewise - i dont think height is an issue as this plant will likely to have winter dieback in your zone - you can keep the plant neat and take out the dead branches every spring...the flowerheads could flop after a rainstorm..

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so the annabelle types will do for you - except the flopping flowerheads...Incrediball would be my pick...try to look for them, they are worth the money...jmho.

Thank you orchidacea for your suggestions. We do have the Annabelles and the Limelight in our area but I was told by the garden centre that they get quite tall, too tall for my needs. I did go out and buy my hydrangea today. I picked Endless Summer, it is not white but more important than color is, I read it is quite reliable and blooms on old and new wood which is good for my area because sometimes we get late frost. Hope I made a good choice. Thanks again.

Endless Summer is a good choice..I have ES in my garden as well...since you are in zone 5, you should expect some winter diebacks on your plant...give them time to bud out and they should bloom for you from July till first heavy frost...I have some clients with issues not getting ES to bloom consistently, yr after yr...but I think most of their problems are - 1) pruning - never prune ES after mid-Aug - if the plant is too big, prune it right after the first set of blooms (usually June)..2) winter protection - for all those north facing ones, a zone 5-6 winter should cause winter diebacks - the flowerbuds will freeze dried and crumble when you look at them in spring...so you can just cut them off, and let the new growth to develop and have blooms on the new growth - at a later date - like in July...3) my experience is that ES is a heavy feeder..I put high phosphate (the middle number in N-P-K - all fertilzer labels have that) one round in spring///and a second 1/2 dose round in Aug...never have problems with ES not blooming...one thing about ES is it will wilt under hot summer sun...if that happens, get it water, and it pop back up in the evening....

good luck with the plants...

orchidacea, thank you for your advice. When you say winter protection, is putting mulch on top of the plant enough or is there something else I should do to protect them.

winter protection - let the plants to tell you when - the plants will go dormant with a series of cold weather - they will lose almost all the leaves...It happens around Thanksgiving time for me here in zone 6b - so for Zone 5 - maybe two weeks earlier...give the plants a lot of water - some people skip this step and they get dead plants the next spring - then mulch around the base(3 to 4 inches with pine bark mulch or pine needles if you find them is what i usually do)...all the leaves should be gone by then...as for the top, some people like to bundle them up, burlap them, even stuff it with leaves and things...but with my ES, I dont do the top wrapping things...sure there will be winter diebacks...and the flowerbuds from the yr before will get freeze dried and crumble...but the ESs just bounce back quick the next spring with new growth and the blooms will be over the new growth...by early April, I would pull away the mulch...what I usually do with winter diebacks is to wait for the plants to leave out - say by Mother's day in my area (New Jersey) and maybe a week or two later in Ontario - and prune the branches on the top where there are no leaves there...also take away the completely bare branches...that way, you keep your plants neat, not so tall, and no ugly dead branches...if you plant Es around the gazebo, you probably will need 6-10 plants or even more depends on the size of the gazebo...wrap and burlap their tops will take some work...and i just dont like the look of it all winter...prefer the more natural look with bare sticks and sometimes the dried out dead blooms from autumn...dont look bad with a snow covered ground..

jmho.

Thanks orchidacea. I planted 7 ES, it is an 8 sided gazebo. I am hoping they will get wide enough so it looks like one continuous flowing bush around the gazebo. I will do the winter protection as per your advice.

Regarding Annabelle's size---I've had mine for 4 years and it is no taller than 3 ft. at best. I have it facing South--it gets afternoon sun.