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Is it possible to grow/maintain in pots trees or shrubs that can offer decent shade for someone to sit under them when there's lots of sun?

I have an open good-sized concrete rooftop in a building and I'd like to have a tree that offers decent shade. The pot can be any size, but it has to be a pot. Or any other ideas besides pots are welcome.

Thanks.

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  • Grow your favorite type of shrub fruit in a bed of almost solid dirt. It should be able to do its thing just fine if the dirt is thick enough, and you get some food in return. – black thumb Jun 12 '16 at 5:05
  • Largely agree with Organic's answer below; although you can grow a deciduous tree up to 15/20 feet in 2 foot depth of soil, it only gets that size if there's plenty of width of soil available, like around 10/12 feet square. – Bamboo Jun 12 '16 at 11:21
  • Location (and climate) could help to narrow the answers. – Giacomo Catenazzi Jun 12 '16 at 15:11
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There are a number of issues with trying to grow a shade tree in a container. To get a good amount of shade you'll need a large container. Large container, lots of soil and water means lots of weight so you need to make sure your roof can support it.

Most trees grown in containers are dwarf varieties that won't get too big and they tend to grow slowly. To get a mature plant that will be large enough to provide shade won't be cheap. Most are grown for ornamental value or possibly for fruit and don't provide much shade. Maybe with a large enough container (huge) you can get something going with maybe a dwarf apple or japanese maple.

I like the concept. I'm not sure it's very practical. I think a better option would be to get a heavy patio umbrella stand and a good patio umbrella. Cheaper, cleaner, easier, faster. You can take it down in the cold months or when it's windy. It doesn't need water and it won't die on you. Create a nice setting to lounge in with some containers with plants you use for ornamental reasons or even some for food production if you want to bring some nature to the space.

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I agree with the other answers (tree in pot will not do much shadow). So I reframe:

There are a lot of plant that you can put in arbor, which will give you a lot of shadow in summer, but relatively light plants, so they could survive well in pots. I like wine grapes: large leaves, relatively rustic.

Google image (rooftop tree / arbor / ..) will give you many interesting ideas (and we can give you an advise with some more concrete plan).

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You can grow trees in pots. Many people do this. But you need a tree that is suitable for the pot, and isn't going to out grow the pot. Containers also tend to easily dry out so you need some way of keeping the tree well watered in hot conditions.

To calculate the size of the tree, you need to know where the sun is at the time you want the shade. If you're on the equator, then the sun will be directly overhead and you won't get much shade from anything without an extensive canopy. If the sun is not directly overhead, then you can calculate using geometry the final height of the tree needed to provide shade.

You may also need to find out the engineering loading for your concrete roof. Concrete is strong in compression, but weak in tension. Likely your roof has been reinforced with steel, but it will still have a rated loading. The reason you need to know this is that some trees keep growing. An oak starts from an acorn. With the wrong choice of trees, you might be exceeding the roof loading specifications.

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