Welcome to NGA, KathyGam. I could not guess exactly how much water you gave them since I am not there to see it. But here are some guidelines:
When to water: insert a finger into the soil to a depth of 4" (or try moisture meters at that depth), the typical depth of new hydrangea roots, to see if the soil is either dry, moist or soggy. Test almost daily in the mornings in the first 2-3 summers. Water the soil -never the leaves- as soon as the soil is almost dry or dry. Maintain the soil mulched with 3-4" of organic mulch (no rock mulch) past the estimated width at maturity on the plant label. Do not water if the soil is already moist before starting to water. Water in the morning (6-8am) so no leaves spend a long time wet overnight.
Water sufficiently: Hydrangeas need copious amount of water in the summer but not on a long term basis as they can get root root. After waiting for the water to percolate, periodically insert a finger to a depth of 8" to ensure the soil is moist; if it is soggy, consider watering less or waiting more for the soil to drain some more; if the soil at that depth is dry, use more water.
Root rot: a typical symptom is wilting of leaves that occurs 24/7 including a few hours after watering in the mornings. A dingle incident of overwatering should not cause root rot. If properly hydrated, the trees should still be wilted daily during the worst/hottest part of the day in the summer. Wilting is promoted, amongst other things, by high temperatures and windy conditions common by the trees' planting locations. Temperatures above 85F will make the foliage lose leaf moisture faster than the roots can absorb more water but if the soil is kept evenly moist, never dry nor soggy, the leaves perk up at night once temperatures recede. When planted in the landscape by themselves, the winds -even slow winds- can help desiccate the foliage so soil humidity monitoring is important until they develop a larger root system. Hydrangea roots are at first tiny, fibrous and very shallow so monitor the top soil humidity, use mulch, and try not to disturb the roots much.
Keep the trees staked for 2-3 years as the root system is still small and they are top heavy.
