Most of the green spaces on rooftops are being used for things like grasses and ornamentals, rather than food. Some things have to be in place before the roof can even be a viable option. Though it is not set in stone, it makes a lot of sense for a good rooftop garden to be on a flat roof. Also, it is critical that a structural engineer be consulted to give the OK for the load bearing or, in simple terms, making sure it can take the weight. Having easy access to the roof is a plus that is hard to beat! Look around at your water situation as well, because if you do not have a convenient way to get water up there, then it's probably a no go. If everything checks out fine then let’s take the next steps up onto the rooftop.
Benefits
On the roof you can add more of a veggie selection if your cover is adequate. What is adequate cover? Well, you can make a hoop house (a plastic cover that will not touch the vegetables) mulch heavy, or even do cold frames. If the roof is cement or better yet, black top, you can easily do onions, lettuce, spinach, carrots, and other colder, tolerant veggies. The sun will bake the roof and the heat will last much longer into the night.
Rooftops can be easier to manage because most of your food will be grown in containers so you will have full control of your soil content. Keeping your containers smaller gives you an advantage of easily testing what nutrients you will need and how much. Smaller containers are easier to water and weed. Your hope is that the plants will grow big and cover the containers making it impossible for weeds to take over anyway.
On the roof your main concern is the weight. Some of the best options we have seen to reduce weight are lighter soils and containers filled only half way. For instance, we chose to do a self-watering earth box filled with organic mushroom compost. Mushroom compost is a lighter soil as it is mixed with mulches of various kinds. Another great soil option is coconut choir mixed with an organic potting mix. I recommend Enivo Grow brand potting soil that is lightweight and packed with nutrients that your plants will need in a contained situation.
There are claims of not using soil at all—just a sheet of plastic and grass clippings. The grass will decay and become a nutritious medium for food growing. More information on that is below in the Web site links. Whatever one decides, it is important to make sure the soil will hold moisture and nutrients.
Obstacles
Sometimes getting on top of a roof is not easy. Unlike walking out to your backyard you either have to climb a ladder, or at least climb a few floors. Even if you have an elevator you still need to get to the top somehow. If you live in a penthouse—great!
Most of us will have the challenge of bringing all those plants and soil up to the roof. With our rooftop garden we had some great volunteers that managed a bucket brigade and a human chain that hoisted all the soil and the plants up to the roof in about 20 minutes. That is the benefit of being in a garden group or in our case, we have the Victory Garden club. The more hands the faster the work gets done. So call all your friends and neighbors for a garden raising party and offer lunch as a big thank you!
Your other main concerns on the rooftop will be wind and heat. It is necessary to prepare for these onslaughts. We are fortunate enough to have a four-foot wall all around our growing space that cuts back the wind pretty nicely. We then nestled our containers next to the knee walls for our wind protection.
Another obstacle is how to get water to the plants. We decided to use self-watering containers. The self-watering containers were homemade from donated, recycled 50-gallon plastic spice drums. They were cut in half, long ways, and then the bottom of each barrel was prepared to hold water without getting the plants’ roots wet. These self-watering container systems are nothing new to the garden world, but are ideal for roof top gardening. We also created a makeshift irrigation system that waters all 14 containers within a few minutes and so we never have to climb up to the roof to water by hand. We are working on having a solar pump, which will take the water from a 250-gallon rain barrel down below and pump up the gray water instead of using city water. Now that’s efficient!
Starting small is a good rule of thumb!!!! You can always expand later once you get a feel for things. We made our self-watering containers in such a way we could add more containers if we chose to later on. We started out with 14 containers and we left room to add up to 30.
A friend, and fellow rooftop gardener, Erik Lindberg started his rooftop garden above his construction business in March 2008. Lindberg mentioned, “The most notable features of the rooftop growing environment is lots of sun! Things grow quite fast. The other is the heat. This can definitely be used to your advantage. My warm weather crops are six weeks ahead of terrestrial farms. Part of it is extensive use of row covers and hoop houses, which are easier on raised beds.”
Lindberg now has one of the first rooftop CSA (Community Supported Agriculture) at about $800 a share. What that means is he offers people a box of food every week for about eight months. Most CSAs cost about $250–$300 a month, but since he is on a rooftop his growing season is extended so he can charge more for the extra months. This helps him offset his cost of about $8,000 for doing a rooftop garden. That included structural reinforcement and building all those raised beds and hoop houses.
Lindberg commented, “The CSA is going pretty well. I heard today that some large CSA farms are doing their first boxes this week. We're into week nine. We've had lots of lettuce and greens, radishes, some broccoli and a turnip, also a few green onions. The only frustration is the extended time between the start of the weekly boxes and the addition of greater varieties of produce beyond greens. Part of this has to do with some random events or perhaps a general disadvantage on the roof for the crops that come between the cold weather ones and the warm weather stuff—things like carrots, beets, peas, and green beans.”
Our rooftop garden at Future Green was a fraction of the cost of Lindberg’s. With soil and materials, the total cost was about $400. I know of one particular rooftop garden on top of a floral shop that ran about $50,000 with a complete greenhouse. So, the sky is the limit. You can spend a lot to save a lot or if you're creative, you can spend very little or offset the cost by selling your produce. Whatever the case, you now have some great ideas for yet another place to put a garden and maybe check out the sunset over a rooftop city horizon.
White House Roof Top Garden
http://www.insideurbangreen.org/2009/01/rooftop-vegetable-garden-.html
A No Soil Roof Top Garden by Gwen Outen
http://origin.www.voanews.com/specialenglish/archive/2004-09/a-2004-09-21-1-1.
Rocket Restaurant Wading Pool Containers
www.cityfarmer.info/rooftop-vegetable-gardener-at-rocket-rooftop-garden-takes-us-on-a-tour/
Future Green’s Self-Watering Container Roof Garden
http://www.futuregreen.net/pages.php?pageid=42
A CSA Garden Share
http://www.jsonline.com/business/47001727.html
