Rooftop gardening and gardening in the ground are VERY different things. There are many factors that you need to consider when rooftop gardening. We have created a guide to some of these factors.
This is based off experience and is our rule of thumb. It’s not proven science...yet.
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| Rooftop garden with Red Cedar and Baptisia by Staghorn NYC (us!) |
PLANTS
When choosing plants, you want to make sure they are super tough and hardy. For help making this selection, check out two of our other posts to read about some super tough perennials and things to consider when selecting rooftop trees.
GROWTH
This applies to growing in planters on ground level or roof level.
Plants grown in the ground grow faster and larger than when grown in planters.
When a plant is grown in ground, it’s roots have ample room to reach and grow. In a planter, roots are limited to the space of the planter. The above-ground plant generally grows as much as its roots can support. When root growth is limited, the above-ground plant’s growth is also limited.
Also, some faster growing plants can become root bound in a planter after time and will need to be repotted. Larger planters allow for more root growth and thus larger plants.
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| Root bound plant |
WINTER
Plants have hardiness zones which are the areas in which they are capable of growing well. This is dependent on the minimum temperatures which the plant can stand. Zone 1 is pretty frigid and zone 12 is the tropics. New York is said to be zone 7.
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| Link to map |
Put that planter on a rooftop and drop it down another zone - zone 5
If you're over 10 stories high, a good rule of thumb is to take it down another zone - zone 4
A good comparison is the bridge freezes before road in the winter - just like a bridge, a planter will lose heat from the top and from the sides, and to an extent from the bottom, causing it to freeze faster. An in-ground garden, like a road, only loses heat from its surface, and otherwise remain insulated by earth
WIND
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| Amsonia blowing in the wind |
Some rooftop/terrace/balcony gardens are taken to the next level of extreme with the wind factor. Depending on how protected or exposed your space is will determine how important the wind factor is in your plant choice.
Evergreens are the only plants that keep their leaves through the frigid, windy winter months. Thus, they are the only ones that experience the worst the wind factor has to give: winter burn. Here is an article about preventing and dealing with winter burn.
The size and shape of your plants will also determine how well they will hold up in the wind. Top heavy plants, ones with large blooms are more susceptible to breaky in the wind. For example, peonies won't do so well, but amsonia is great.
WATER
Since planters are confined spaces, they can dry out pretty quickly, especially on a dry, windy, sunny day on a rooftop. They should be watered between 4-5 times a week depending on the size/depth of the planter.
We highly recommend irrigation systems to all of our clients, friends, families, and complete strangers. They save lives, plant lives.
PLANTERS
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| Planter garden by Staghorn NYC |
Wood - Be careful here. Quality wood and craftsmanship can give you a great planter that'll look beautiful and last years. We recommend going with custom built. If you can’t, make sure it’s good quality teak, cedar, or ipe, otherwise you’re looking at a rotten mess a few years down the line.
Fiberstone - A good buy, pricey, but worth it. Comes in nice colors, very lightweight and easy to move, super sturdy, and won't crack in winter.
Metal - Wouldn’t mess with anything outside of Cor-Ten steel
Plastic - May surprise you with some positives, but it’s plastic, so manage those expectations.
