Mother's Day hydrangeas are usually mopheads although you could see a few lacecaps in there sometimes too.
Down here in the South, hydrangeas definitely act different from way up in MI. My aunt -RIP- in Ocala and I in Tx have had to place them so they will get shade in the summer between 11am to 12pm (so no afternoon or evening sun). Even just a couple of hours of morning sun or just dappled sun are enough in the summer. In year 1's summer, you may have to give them extra shade (think using an outside chair, newspaper, shade cloth or umbrella).... as some hydrangeas have leaves developed in greenhouses that coddled them with nice temps only and with limited sunshine, definitely not what they will get outside in FL.
I am guessing without pics of the leaves but if you notice that the leaf edges get brownish/darkish from the edges inwards, they may need more water. Down here, I give them -in Spring- 1 gallon of water per watering per plant to a newly purchased potted shrub from -say- Lowes (just to give you an idea of height/width). In your soil, consider 50% more water per watering as sandy soil drains too well and lacks nutrients. In mid to late May, I give them more water and in September I go back down to 1 gallon. Once they loose the leaves, I water every week or every two weeks, depending on whether it is dry. I doubt you can do that if your soil is sandy though; you may have to test things around during their first winter.
In late May and thru early Fall, when we get long periods in the 90s or daily 100s in mid/late May then I increase that to 1.5 gallons and in some weeks, I may hand water a bit too. Normally, I try to do drip irrigation twice a week but in the summer, it kind of misses giving enough moisture to these water hungry plants so I water manually with a hose instead of using the drip. One always has to be careful of overwatering as this can cause root rot but with sandy soil, the superb drainage of sand will help minimize overwatering issues (but note I did not say that it will prevent them!!! Hee hee hee!). ;o)
To keep from under or over watering (that was your concern), test the soil by inserting a finger to a depth of 4" and water only if it feels dry or almost dry. Do this daily in the morning 6am ish for 2-3 weeks. Each time that you water, make a note in a wall calendar. After the 2-3 weeks, average out how often you had to water (every 3 days or every 4 days etc). Then set the sprinkler or drip irrigation to water "x" gallons of water per watering in Spring. Always water the soil (never the leaves) early in the mornings 6am ish & water manually from the base/crown outwards to cover the width of the pot in which the shrub came (that is where the roots currently are). Note: you can also get a moisture meter.
Since sand has little minerals, give it a layer of organic compost several times a year. You can also add some liquid seaweed to the water if manually watering. For a fertilizer, you can use about 1 cup of organic compost, composted manure, cottonseed meal or a slow-release, general purpose chemical fertilizer with a NPK Ratio of 10-10-10. Hydrangeas are not heavy feeders like roses but in sandy soil, it may be useful to give them more than a single fertilizer application per year. Say one in late winter or early spring, depending when you observe that they leaf out. Then again in the Fall when temperatures moderate. In Ocala, the hottest part of the summer on average was mid July to early August but it would take until mid September for average high temps to go below 85F. That is the point above which hydrangeas like to "sulk": when it gets that warm, they can be prone to wilting episodes.
If you see an extreme wilting episode, give them 1 gallon of water per plant from the crown outwards. But they should pick up and get better on their own by the next morning IF the soil is already moist. What happens is that, at high temps or on windy days, the leaves loose moisture faster than the roots can absorb water. Then the shrub wilts to compensate. If it has enough water in the soil, it recovers overnight on its own. Use the finger method or a moisture meter if you need help telling if the soil is dry or not.
Maintain 2-4" of organic mulch (no rocks in the mulch) year around and replenish it when you see that is has been blown off by the winds. Hydrangeas here can feed off the decomposing mulch too but I recommend adding ferts in Spring aaaand in the Fall. If you prefer, you can use a low nitrogen fertilizer in the Fall.
The leaves may, in some years, stay "on" the shrub and when leaf out time comes, they will strangely "disappear" after the new ones get large enough.
Luis
