Rooftop gardens are nothing new. City dwellers have been tucking plants on roofs and fire escapes for generations. Even green roofs, roofs covered with soil and plants, have been around for years. No matter how much land we have, we always seem to be looking for more space! There are also plenty of wonderful plants for rooftop gardens that every gardener can choose from, and so here’s why you should consider setting up your very own rooftop garden:
- They make use of unused or underused space
- A garden beautifies an eyesore
- They can provide privacy
- They can be extremely environmentally friendly
- There is usually good sun exposure
- No deer!
If you’re considering a rooftop garden, there are a couple of directions you could go in. Fully planted green roofs, where the roof is covered with soil and the plants are in the ground, make great environmental sense, but they are too difficult for homeowners to undertake on their own. Green roofs can easily top 100 lbs.
The easiest and most personal approach to rooftop gardening is the use of containers and raised beds. You can create any style of rooftop garden with container grown plants, from a few simple herb plants to a formal, elegant potager. Containers are perfect for rooftop gardens because they are light, portable, flexible and affordable.
Starting a Rooftop Garden
Urban rooftop gardens can be an oasis in an otherwise built up urban setting, but before you start planting, there are several things to consider about urban rooftop gardening. If you’ve gone through the logistics and have decided to create your own rooftop garden, here’s how to get started – and what you will need to do it right.
Containers are one of the most expressive components of a rooftop garden. This is not to say you need to spend a fortune on them, although you easily could. Besides aesthetics, the things to keep in mind when choosing your rooftop containers are their size, weight and material.
You will need containers large enough for the roots of whatever plants you choose. The amount of soil needed will vary, so research your choices before you plant them. You will find a lot of plants labeled as “Great for containers.”
The weight of the container becomes an issue if you are worried about how much your rooftop can support. Remember, containers get even heavier when you water them. Traditional materials, like clay, terra cotta and cement can be quite heavy. Plastic pots and the newer synthetic containers are light enough to lift. But you also need to consider balancing the height of your plants. A tall or top-heavy plant, like a small tree or a tomato plant full of ripening fruits will topple over in a lightweight pot. If your rooftop garden is windy, heavier containers will be a must.
Clay, terra cotta and ceramic pots also tend to heat up more than synthetics. When the pot heats up, the soil and roots heat up, requiring more frequent watering. You can help somewhat with a little shade and mulching the top of the containers, but drip irrigation will make your life much easier. This is the reason many people prefer fiberglass planters on their rooftop gardens, so make sure you take a look at our extensive collection of fiberglass planters.
Soil is often the last thing to interest a new gardener, but it is the most important part of your garden. Good soil means healthy plants and less work for you. If you grow your plants in containers and raised beds, you will have the advantage of bringing in soil. There are several good potting mixes on the market or you can mix your own by combining 3 parts compost or composted manure with 1/4 part peat, for lightness. Add a handful of perlite per pot, for improved drainage.
Soil in containers needs to be replaced periodically, usually every spring. You can lift and repot or simply top dress the existing soil.
Container plants will require regular fertilizer. Even a great potting mix will become depleted over time, as plants take up the nutrients and the water leaches them out. The larger a plant grows, and the more water it takes, the faster the soil is depleted. The type of fertilizer you use will determine how often you will need to fertilize, but every 2–3 weeks should be sufficient.
There are many good fertilizers on the market, including increasingly more organic choice. A water soluble fertilizer is the fastest way to get the nutrients to your plants, either by watering the soil and getting it directly to the roots, or by foliage feeding.
You’ll need far less tools for a rooftop container garden than you would for a traditional ground level garden. You’ll be doing a lot of scooping and filling. A trowel and perhaps a soil scoop are the first tools you’ll need. A small tarp will come in handy when you are emptying soil, to keep from making a mess.
The only other essential tool would be a good pair of pruners, to prune and clean plants. After that, it all depends on what you’re growing and how much maintenance you intend to do.
Unfortunately, even a rooftop garden will be subject to pests and problems. Insects can fly, as can spores, so you will still need to monitor your plants and try to catch problems while they’re small. Keep your plants healthy and stress free by keeping them fed and watered, and you will limit their problems.
You can plant virtually anything in a container. Since most rooftop gardens get very hot during the day, drought tolerant plants are recommended for urban rooftop gardens. You will also need to take into account your sun exposure and hardiness zone. Since rooftops hold heat, they can create microclimates that hover about a zone higher than a garden on the ground would be. You’ll need plants that can handle the heat, but since they are in containers, they probably won’t have better cold tolerance than ground planted gardens.
There is no list of certified rooftop hardy plants. Your choice of plants will require some trial and error. Honestly, with the exception of tall trees, there is little you can’t grow on a rooftop. Many rooftops are little micro climates that can overwinter plants that would not be hardy at ground level. And if you have the space and are willing, you can bring tender plants indoors for the winter. Annuals will require more frequent watering, but will eat up the sun.
Some good rooftop plant choices would be plants with limited root systems, that don’t need a lot of soil, like herbs and vegetables, smaller to mid-sized perennials. Trees and shrubs require more soil and larger pots, but you need less of them to make an impact.
A Few Great Plants for Rooftop Gardens
Depending on the intended look and function, there is a virtually unlimited list of plants for rooftop gardens that you will be picking from. Here are some of our favorites, sorted by category:
1. Flowers: Transform your roof into a colorful flower garden with roses, begonias, petunias or pansies. In warmer climates, you will also have a range of exotic flowers at your disposal.
2. Veggies: Why not actually grow something edible? Tomatoes, radishes, peppers, cucumbers, broccoli, zucchini, lettuce… Just some of your easy-growing options here!
3. Herbs: Some of the easiest potted plants to grow, including basil, chive, parsley, thyme and mint. Perfect for adding an extra bit of flavor to your cuisine!
4. Perennials and succulents: An endless array of your options here includes great perennials such as various grasses, ferns, and composites like daisies and asters, as well as extremely low-maintenance succulents in cacti and aloes.
5. Dwarf trees and shrubs: Go for ornamental trees and shrubs like Japanese maples, crabapples or lemon trees, as well as dwarf conifers, junipers and pines. Get a big pot for these – but do make sure your roof can take the extra weight!
6. Vines and climbers: A wonderful solution if you’d like to add some privacy to your rooftop garden, some of your best options including clematis, honeysuckle, ivy and the Virginia creeper.
Practicalities to Consider
While caring for container-grown plants on a rooftop is much like maintaining containers on the ground, there are a few rooftop idiosyncrasies to consider, before you start hauling your pots outside:
1. Permission: First, check with your landlord and/or building code. Questions like accessibility, building height restrictions and fire regulations can prohibit any type of roof use.
2. Structural Integrity: Make sure the roof can hold the load. Get a licensed pro to do this. Soil and pots are heavy to begin with and will get heavier as the plants grow. If you’ve ever tried to move a pot full of wet soil, you know how much weight water can add.
3. Access: How are you going to get your materials and supplies in and out? If you live in an apartment, make sure you are allowed to use the elevator. Some municipalities require multiple access/exits and possibly exit lighting, fire alarms and emergency lighting.
4. Water: Will you be able to run a hose out to the roof? Watering cans can become a nuisance and containers require a lot of water. Consider installing a rain barrel and drip irrigation.
5. Sun Exposure: Are you shaded by nearby buildings or the terrace above you? Even full sun can be a problem, when plants are sweltering on top of concrete.
6. Heat: Besides the sun beating down on the roof, there is ambient heat reflected from the roof surface, surrounding buildings, street cars and metal exhaust and utility structures. You will probably want to provide some sort of shade, if not for the plants, then for yourself.
7. Wind: Wind can whip down straight urban streets, especially on high rises. You may want to consider some type of wall or fencing. If so, you will probably need to check your building code again for required heights and structural stability. This is especially important when building safety barriers for kids and pets.
8. Privacy: Many rooftops are surrounded by neighboring buildings. If your rooftop garden will be in full view, you may want to plan for screening. You can plant a hedge of evergreens, run vines up a trellis wall or simply tuck under an umbrella table.
9. Electrical Wiring: Electricity isn’t essential, but it sure makes things easier. If you are planning on enjoying your garden at night, candles are the best lighting for weeding.
10. Storage: There’s a lot of paraphernalia associated with gardening: tools, fertilizer, compost, buckets… Space is limited on a rooftop and it’s hard to camouflage a storage area. Shelves will suffice. Some rooftop gardeners opt for narrow closets. Another option is bench seating with built in storage, to do double duty.
11. Cost: Last but not least, how much are you willing to spend? You can start small and add on, buying more pots and plants (and soil) as you go. The real expense comes when you want to start hardscaping and building on the roof. Laying tiles or stone, building raised beds and boxes, adding lighting and furniture can all start to add up. Plus, you may need more structural work to support them.