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.

Just going to wing it...as I do most things. LOL So will move this on down. josh

Bumping this because I have the same question. Planted a copper beech (Fagus sylvatica riversii) on the south side near the window and it appears to have croaked, don't know why. Another one fairly nearby croaked Spring 06. So although the copper beech is Lynn's favorite tree, we don't want to plant another one there to take its place. Discouraging to spend so much $$$ on trees that expire. This tree will get morning afternoon and evening sun and thus heat in summer. Eventually if the sequoias around it survive it will get some shade but it'll be near the roof so all that sun will hit it blazing over the roof. Resin, I'd love to use a purple oak if I could find one. A purple evergreen oak would be even better! Everything around this tree is blue or green so we're aiming for copper or purple foliage. It's a wet spot near a creeklet but we can build it up in a berm a bit. It's right by THE busiest bird feeding frenzy I've ever seen (pictures maybe by tonight) so its branches should be able to handle continual bird fluttering landings and take offs. Suggestions please!

Take a three day break and use your hygrometer or simply your index finger to feel if the soil is moist to the knuckle of your finger. If so, don't water. You really want the soil to not completely dry out between watering times, but not too much. Moist is good but saturated isn't the best scenario for Arborvitae. The good news is that Arborvitae can handle a lot of water. There's no need to water every day. During heat spells a 45-60 minute watering 2x a week should be sufficient given they are mulched and 1x a week when less heat. Use your gauge or finger to see how your particular soil is holding water or drying. Dax