Maintaining a new urban rooftop container garden

Question

Watering instructions to give the building engineer who will be managing the garden. How often to water 4 3-foot rail planters of annuals, 55 zon5 with coco liners, 3 potted arborvitae trees, 2 deck planters under a trellis with climbing plants, and a few larger potted perennial plantings?

Answer 1

Unfortunately, there’s no way to give an answer to your question, because the amount of water to give the containers you describe can vary weekly depending on the weather, the soil, and the plants. The sun changes, the temperature changes, the wind changes; different kinds of soil drain differently, and change as they age and roots grow; the plants’ needs change as they grow – or don’t grow – and I have no idea what kinds of plants you’re using. As a gross generalization, I would say that each container needs to be watered to runoff maybe every day or every other day in summer, maybe once or twice a week in spring and fall….do you have provisions for drainage, or is all the water confined to the containers? That would change the amount of water hugely. And what about winter?
Unless your building engineer also happens to be a horticulturist, I’m afraid you’re not going to be happy with the results of your experiment. The only real suggestion I can give you is to contact an interior landscaping company in your city, so you can have professionals take care of your garden. Hopefully you have not completed the installation of your garden, so you can get some professional input there, too. Here are a couple of articles that may give you more of an idea of considerations: https://www.gardeningknowhow.com/special/urban/creating-your-own-rooftop-garden.htm
https://www.gardeningknowhow.com/special/containers/how-to-grow-container-trees.htm