Answer: Hydrangeas do need an evenly moist soil, it should be damp like a wrung out sponge but not sopping wet or saturated. You will need to water to supplement rain -- feel the soil to see if you need to water yet or not. Terra cotta that is not sealed is porous and allows moisture to evaporate from the soil much faster than it would in a plastic container so check this daily. In dry spells or in windy weather or in warmer weather you may have to water daily, especially as the shrubs grow larger in proportion to their root space. They should never be wilted in the morning, if they are wilty in the morning they are far too dry. By August they may droop a bit during late afternoon if they are in hot afternoon sun, but if the soil is adequately moist they should perk up again when it cools off.
Hydrangeas are a bit blowsy but should be self supporting. The blooms often weigh down the branch tips with lower ones reaching the ground and giving the overall plant a rounded look so it is not stiffly upright. Sometimes a heavy rain storm will splay them out temporarily but they should stand back up on their own. If they are flopping badly they may need more sun and/or they may be overfertilized. They need direct morning sun or very bright dappled light all day.
If you are fertilizing, you should use something with an analysis like 10-20-10 plus minors either slow release or water soluble -- and do not exceed the label rate. If your potting mix included a fertilizer you may not need to feed it for several months.
You can try to prop them up but they do need to have air circulation through the center of the plant so don't truss them tightly. I hope this helps.
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