Welcome to NGA, JuniperBushes. Hydrangeas are water hungry plants that require some amount of monitoring during their first few summers. It is then when they get affected by heat stress. Heat stress covers several scenarios: temperatures have risen above 85F almost daily, the leaves get some amount of direct sunlight and the plant gets drying summer breezes.
But those three are a small part of the wilting cause. An even larger component is that the shrub is not yet established in the garden and the leaves are not used to a lot of sun. "Not established" is a fancy way of saying that the plants roots were cut to fit into the plastic pots used in the plant nursery. It will take 1-3 years until they become bigger and the plant becomes established.
Hydrangeas typically have very large leaves and, in the summer, when the leaves get stressed by one of those three scenarios that I mentioned, those leaves begin to loose moisture much faster than the roots can absorb water. As a result of this imbalance, the leaves droop or wilt. But not to worry. If the soil is kept as evenly moist as you can (no periods of moist soil, then dry soil, then moist soil, etc), the leaves recover and wake up looking normal and perky in the morning.
What I do in Tx during the summer months is thus to check them in the morning.. and water them if they are wilted. During the afternoons, I do not water them on the spot if I catch them wilting. If I see them wilting during the day and the soil feels moist, I leave them alone and let them fix themselves at night. However, should I encounter an extreme looking episode during the day, I give the plant 1 gallon of water on the spot.
Can you get wilting if you water? Yes, it is possible to see wilting on the day that you watered, even if the soil remains moist to the touch. That is because the plant has a small root system and the leaves loose moisture faster than the roots can absorb more water when heat stressed or when it is very windy. The leaves wilt and that is a nice thing as it reduces how much leaf surface area the sun will be hitting (remember that when wilted, the leaves are pointing down so it is harder for the sunlight to hit them that way). And yes, you can water multiple times a day if your soil drains well, like they do with hydrangeas in some city gardens or in places with partly sandy soil.
Can you water any time that you see wilting? Yes, you can but be careful.... there is a risk associated with that when the plant is in the ground (less risk if it is in a pot). If your soil drains well, the water may help perk them up during the day. But if the soil does not drain well (I have clay soil), there is a risk that the roots will sit in wet/soggy conditions and, after too much of that, the roots can develop root rot.
How do you tell if they "reeeeeally" need water? Use the finger method: insert a finger into the soil to a depth of 4" and see if the soil feels dry or almost dry. If the soil is dry/almost dry then give them water. Otherwise, monitor and hold the water.
You can use the finger method also in this way to help tell when to water, when to change watering amounts and minimize the chance of over watering: for 2-3 weeks, use the finger method every (early) morning. When you decide to water because the soil feels dry/almost dry, make a note in a wall calendar or electronic calendar. After 2-3 weeks, review the information in the calendar and determine, on average mind you, how often you watered. That may be something like every 2 days, 3 days, etc. Then set the sprinkler to water every 2/3/etc days. When you observe that temperatures have gone up 10-15 degrees higher/lower almost every day and stay there, consider using the finger method for another 2-3 weeks to see if you need to tweak things.
What else can you do? Keep them well mulched year around, say about 2-4" of organic mulch but do not use rocks as mulch. It takes new hydrangeas about 1-3 years to become established in the garden and grow a large set of roots. In the meantime, during the worst of the summer or in very windy days, consider putting some sort of wind block or using an umbrella or outside chair to give the plant extra shade in the afternoon or in the evening. If you use a sprinkler, you can also water the hydrangea early in the morning, near sunrise, so the leaves are not kept wet for long periods, something that promotes powdery mildew and cercospora leaf spot (fungal infections). You can also use drip irrigation or soaker hoses to water hydrangeas. I tried the soaker hoses but wild bunnies literally ate a big hole on the hose in my first night trying the soaker hoses. Sigh.... Eventually, my sprinkler broke and I switched to drip irrigation. Saves me a little money since it is so hot down here in the summer and I have to water most plants so much more than when I lived in Atlanta.
So how much should you water? Start with these suggestions and tweak (based on soil types, etc) up or down. When you see leaf out in the Spring, give it about 1 gallon. As temperatures are regularly above 85F most days and stay there, increase to summer levels of 1.5 to 2 gallons. As temperatures moderate and are regularly below 85F most times, go back down to 1 gallon. When the plant goes dormant, water once a week or once every two weeks depending on local rains. Stop watering if the soil freezes but resume when you see leaf out.
About variegated hydrangeas... yellow or white variegated hydrangeas do better with less sun than typical mopheads. I did not have space for Big Daddy (Lemon Daddy's parent) so I got Sun Goddess instead and noticed that the intense sun in the South made the leaves eventually turn from yellow to dark green. That may not be an issue where you are though. For example, in the Pacific Northwest, I have observed several yellow hydrangeas still very yellow this time of the year (but not here). To help maintain leaves yellow, you can go plant in locations where the morning sun hits for just a little bit, say, 1-2 hours without having major blooming issues. LD will produce blooms that are either pink (if your soil is alkaline) or blue (if your soil is acidic). I did not like the shade of pink of my SG against its yellow leaves and ended cutting the blooms off after a month or less. Not a big deal as I got it for the look of the yellow leaves. Ha!
About Lemon Daddy... without winter protection, it may not bloom reliably in cold zones. Many places in cold zones like 5 sell it, knowing that they will never produce blooms but also knowing that many people buy it just for the leaves. If you decide you like the bloomage, I encourage you to winter protect it when it goes dormant in the Fall and to remove the winter protection about 1-2 weeks after your average date of last frost.
About flower buds... these hydrangeas -like LD- produce flower buds in late Summer to early Fall (earlier in the South; later in the north and Canada). We often use the phraseology that these shrubs bloom on old wood only. Down here, for example, they produce the flower buds around mid to early July. Then flower buds develop at the ends of the stems and are invisible until they open in the Spring. To preserve the flower buds, try not to prune stems if you can help it. Place LD in a location where it can attain the dimensions in the plant label without touching other plants, etc. To preserve the flower buds if weather is too cold, consider winter protection. If winter temperatures and drying winds kill the stems, you get no bloomage. If the stems are not killed but it gets cold enough to kill the flower buds, you would not get bloomage either.
As the shrub becomes established (that is, the shrub develops more roots), the wilting episodes will be reduced but not eliminated. In future summers (or very windy days) I would still do a cursory check in the mornings to see if the hydrangea is wilting and did not recover on its own overnight.
Does that help you?
Luis
