I fear that the choice of plant puts you at a disadvantage from the off. Your shrub looks like Sambucus 'Black Lace' or similar cultivar. This is a vigorous shrub hailing from cool, moist, temperate climates which can potentially reach 8 feet with a large root ball. I am afraid that trying to grow it in a small pot (and it is small for an elder) on a roof top in NYC is going to be a huge challenge. You refer to 'only' 80 degree heat. That is incredibly hot for elder. Even the wild ones here droop in that kind of temperature and they have roots down in the moist ground. Basically your elder is being cooked.

It will need a much bigger container, something like a half barrel, much cooler temperatures and copious watering to survive.

I think Black Lace Elderberry was overhyped, which is why you don't see it hyped anymore. It's a disappointing shrub. I bought six in 2" pots five years ago. I kept them in containers for a season and two survived winter in the garage. The remaining two went into the ground in a berm with excellent amended soil. One lived, and that one took three more years to do ANYTHING.

But the thing is, it is now thriving, even in the intense Kansas heat and drought. I water, but I'm sure I don't water it enough because we've developed two of our three acres and we water a lot. It bloomed this year, but wasn't too prolific.

Would I put in more of them? No way.

Bought Black Lace around 2008 and quickly decided it was going to be too big for the space I put it in. Moved it to where it is now on the northwest side of my house and I still have to keep it in check with heavy pruning. I love it though.

I agree that the pot is too small for the elderberry and needs to be in a barrel.

As you can see from this picture taken in May, it is growing out into the sidewalk already and I cut it back to about 2 feet in February.
Vickie

Thanks everyone. I will re-pot and try again. For now, I went with situating other plants around it to try and reduce heat gain. Come the weekend, I will size up to something like a half barrel. Since it's a rooftop and south-facing, do you think it will prefer longer or shorter exposure to the morning sun? Essentially, no matter where it is, it will get easily 6 hours in the summer, if not 8-9. The choices are 8-9 hours and morning vs. afternoon. So, 6 or 7am-1 or 2pm or 1 or 2pm to 7 or 8pm. In the winter, the hours will obviously be less, and that is my concern. Morning sun in the wintertime in a rooftop NYC garden - what do you think (assuming it makes it through the summer). Btw, blue23rose, your elderberry looks wonderful!

My 'Black Lace' elderberry is about 10' tall. These are fast-growing, vigorous, very large shrubs that are not suited for pots. sunauna, elderberry is deciduous and dormant in winter so the amount of sun it gets in winter doesn't matter. If it's frying (all mine are in full sun but they are in the ground with adequate moisture and don't burn, even in the hottest part of summer), try to place it where it doesn't get the afternoon sun. This is going to be a labor of love, and your plant likely will never look like blue23rose's, but that doesn't mean that you shouldn't have some fun trying.

Sara

Thanks, sunauna. Good luck with your elderberry in the bigger barrel.

The one thing about gardening, it is definitely trial and error. And if one plant doesn't work, your local nursery can suggest something that would work for your rooftop.

Vickie

I purchased one of these last spring and because the spot I wanted to plant it was not ready I moved it to a barrel planter for the summer. That fall, only a few months later, I was ready to plant it in its permanent spot. I figured it would be a breeze because the plant barely grew at all. To my surprise the entire barrel was filled with a big mass of roots. HUGE. From a 3 gallon container to a full barrel. That pot needs to be much bigger.
This spring I dug the plant up and gave it to a neighbor. Beautiful plant that I loved but it kept getting wilted stems due to these little green worms that dig into the stems. Borers I think they are called. It was annoying.