How to Transform Your Rooftop (or Other Small Outdoor Space) Into a Garden

Pick the right plants.

According to Frymark, tender herbs like basil, cilantro, parsley, mint, and dill will all grow well on a small balcony in pots. Steer clear of growing rosemary or thyme in a small space, as they're slower to grow and may not produce as much in this type of environment. For veggies, leafy greens and arugula can also be grown in containers on a small balcony and harvested several times before replanting. If your space is super sunny, cherry tomatoes are also a great option to grow in pots (just make sure you have some kind of trellis or cage to support them as they grow). Edible flowers like nasturtiums and violets are another great option—they look beautiful, too.

If you'll be growing plants indoors, jade, spider plants, and pothos are a great place for beginner gardeners to start as they're resilient, low maintenance, and thrive in both the city and the suburbs. All of these plants do well in low light environments but still thrive best by a window. And you only need to give them a little bit of water every week to ten days (except when your spider plant starts to get very leafy).

Be wise about watering.

Knowing how much water to give your plant can be tricky, as it all depends on the type of plant and the amount of direct sunlight it's receiving. Don't be afraid to get your hands dirty—go ahead and stick your fingers in the soil to make sure the soil is moist throughout the pot, not just at the top. If you're planting herbs in a window box, make sure to add rocks at the base to ensure proper drainage. A very common mistake is over-watering potted plants, which causes root rot. You never want your potted plants to be sitting with their roots in water.

Know the difference in how you care for herbs vs. decorative plants.

Herbs are faster growing and will need to be watered more frequently, especially when they are outdoors. Vegetables and herbs will also need plant food as they grow, which you can easily pick up at your local garden center.

The herbs will also need pruning and cutting. To harvest, snip the stem just above the point where two large leaves meet and make sure to pick the leaves regularly to encourage growth. Regular clipping encourages a more rounded plant but be sure to harvest only up to two-thirds of the plant so that it can continue producing. Harvest before the plant flowers. If you can't, just pinch off the flowering portion. In addition to sowing herbs from seed, a cutting of most herbs will easily root when placed in water. Select a 4-inch section of an herb plant that has not yet flowered and roots will form within a week.

Select the right soil.

An organic and well-draining potting soil will do the trick. You can also add a slow release fertilizer to the pots before you plant. Once it is time to plant, follow the instructions on the seed pack for instructions on how far to space the plants so they have enough rooms as they grow.

Optimize sun exposure.

Vegetables and herbs like a lot of light—full sun all day! (Some shade is OK but the more shade they have, the slower they will grow.) The indoor plants will do best in a south- or west-facing window. Another genius trick: it helps to rotate the pots once in a while to keep the growth balance and not only in one direction.

What do we need to know about pollution?

"Plants are a great way to reduce the effects of pollution within a city," says Frymark. "Trees, shrubs, an herb garden, and even houseplants all help us reduce the amount of carbon dioxide in the air, increasing oxygen and eliminating toxins."

Note that when gardening in the city, one of the biggest challenges can be soil quality. Cities don't have a ton of arable land or fertile soil and tend to have high levels of metal due to years of industrial activities, poor land use, and vehicle exhaust. Before planting a garden in the ground outside, consider how the land has been used in the past as it may contain pesticides and herbicide, lead, or oil and other petroleum products. The best way to ensure your soil is safe is to check with your county or city planning department. You can usually obtain a soil test for free or at a low cost through your local county extension office.