Colin McCrate & Hilary Dahl’s Rooftop Farm

In urban areas with little open land, gardeners are turning to rooftops to grow food. Colin McCrate and Hilary Dahl have transformed a barren rooftop into an urban oasis with room for a variety of potted and raised-bed crops, as well as a pergola-covered seating area topped by a hops vine.

• Raised beds and half-barrel planters provide plenty of growing space for crops
• A hop-covered pergola creates a cozy spot for outdoor gatherings and meals
• Beehives ensure pollination of the fruiting crops and supply homegrown honey

The folks at the Seattle Urban Farm Company, founded by Colin McCrate and Brad Halm, want to see more rooftops put into food production. “Rooftops are an incredibly underutilized resource,” says Colin. “Creating food-producing green spaces seems like a great way to get more value from our urban land.” He cites many benefits of rooftop farming, including reducing storm water runoff, lowering energy bills, and cooling the environment. A big benefit is the satisfaction of creating a space that is relaxing yet able to produce a surprisingly large volume of food. “Whether it is a community garden on an apartment building, a production garden for a restaurant, or a market garden, thousands of pounds of produce can be grown right above our homes and offices,” he says.

Overcoming difficult conditions.Gardening on an exposed rooftop does offer its share of challenges, however. “Rooftops can be much windier and have more extreme temperatures (hotter and colder) than at ground level,” warns Colin. Because containers and beds have limited soil depth on rooftops, the soil needs to be consistently amended with high-quality composts and fertilizers. Colin also notes that it is easy to over- or underfertilize crops in containers, and he recommends yearly pH and soil nutrient tests.

Planting in barrels. Colin and Hilary have included nine half-barrel planters for edibles and annual flowers, as well as six cedar-framed raised beds measuring 4 by 6 feet. They recommend that the beds be at least 10 to 12 inches deep to preserve moisture and make it easier to maintain adequate nutrient levels. The two dwarf fruit trees should also be planted in half-barrel planters or containers of a similar size. Columnar apples stay small with minimal pruning and thrive in containers.

To make the most of limited space, Colin recommends succession planting, amending the soil and sowing another crop as soon as the initial crop has been harvested. He advises adding a small amount of compost and organic fertilizers to each bed between crops and occasionally boosting crops with compost tea or a liquid organic fertilizer.

Colin’s Tips for Success on a Rooftop

• Look into access. Make sure that you have easy access to the roof space (to transport materials up and down).
• Consult with the building engineer. Check that the roof can support the weight of the garden (and the gardeners!). Also make sure that the garden construction and management will not damage the roof membrane.
• Find a water source. Use an automatic watering system to cut down on the work you need to do. Rooftop beds can dry out quickly, and during the hottest parts of the year may need water two to three times a day. Your garden has a much better chance of success if it receives regular, timely irrigation.
• Use sturdy materials and secure them well. Rooftop gardens need to withstand high winds and extreme temperatures. Wind-blown materials could present a serious danger.
• Use appropriately sized containers for the crops you want to grow. We like to use a half-wine-barrel planter for dwarf trees like columnar apples, Meyer lemons, and bay laurel, and shrubs like blueberries. Half a wine barrel holds around 30 gallons (4 cubic feet) of potting soil.
• Pick the right planting medium. Seattle Urban Farm Company uses a pre-mixed organic potting soil for rooftop crops that are planted in containers and raised beds. It’s lighter than typical garden soil and it won’t compact over time. They amend soil with organic fertilizers before planting.
• Look for a storage space. You’ll need it to keep fertilizers, extra bags of compost, tools, and other supplies organized and handy.
• Consider your crop choices. Grow the right plants at the right time and in the right place. Certain crops, like salad greens, benefit from some shading in summer, but they also thrive in the spring and fall garden. If growing tall, trellised crops like pole beans, tomatoes, and cucumbers, make sure your supports are adequate and the plants are sheltered from the wind.

Lush sanctuary. Colin and Hilary’s plan was to grow edible crops, but also to create a small sanctuary in the middle of the city. They have included a cozy seating area, which is tucked in a corner of the garden under the shelter of a hop-covered pergola. “The hops are a deciduous vine and will provide a break from the heat in the summer, while allowing for a nice sunny spot during the cooler months,” says Colin.

Help for urban bees. A rooftop is also a great place for urban bees, and Colin and Hilary have included three hives in this plan. “Rooftops are out-of-the-way, sunny locations, so they provide an opportunity to increase the number of urban bees while keeping stinging hazards on ground level to a minimum,” Colin says. With the decline in bee populations, Colin says that many urbanites are setting up hives to help bolster the populations, with the bonus of collecting honey.

Colin & Hilary’s Garden Plan

For Raised Beds

1. Assorted greens: ‘Deer Tongue’, ‘Nancy’, ‘Winter Density’, and ‘Breen’ lettuce; ‘Surrey’ and ‘Roquette’ arugula; ‘Calypso’ and ‘Santo’ cilantro

2. Beets: ‘Napoli’, ‘Scarlet Nantes’, and ‘Purple Haze’ carrots; ‘Early Wonder’, ‘Chioggia’, and ‘Touchstone Gold’

3. Onions: ‘Red Rezan’, ‘Polish White’, and ‘French Pink’ garlic; ‘Ailsa Craig’, ‘Prince’, and ‘Ruby Ring’

4. Perennial herbs: Italian oregano, ‘Aureum’ golden oregano, Greek oregano, common (English) or ‘French’ thyme, peppermint, and rosemary

5. Kale, broccoli, and Swiss chard: ‘Toscano’, ‘Rainbow Lacinato’, and ‘White Russian’ kale; ‘Bay Meadows’ and ‘Arcadia’ broccoli; ‘Bright Lights’ Swiss chard

6. Strawberries: ‘Seascape’

For Half-Barrel Containers

7. Hot peppers: ‘Thai Hot’, ‘Early Jalapeño’, ‘Ancho’, and ‘Fish’

8. Dwarf fruit trees: ‘North Pole’ and ‘Golden Sentinel’ columnar apples (need two different apple cultivars with corresponding blooming times to ensure pollination)

9. Annual flowers: Good choices to support the bee population include calendulas and nasturtiums (edible flowers), anise hyssop (edible leaves), and sweet alyssum and lobelia (nonedible ornamentals)

10. Squash: ‘Zephyr’ and ‘Gentry’ summer squash; ‘Jackpot’ zucchini

11. Potatoes: ‘Yukon Gold’, ‘All Blue’, and ‘Colorado Rose’

For Trellis/Arbor

12. Tomatoes: ‘Black Prince’, ‘Pineapple’, ‘Sungold’, ‘Black Cherry’, ‘San Marzano’, and ‘Brandywine’ (trellised)

13. Hops: ‘Cascade’, ‘Centennial’, or ‘Willamette’

14. Cucumbers: ‘Marketmore 76’, ‘Suyo Long’, and ‘Lemon’ (trellised)

15. Pole beans: ‘Fortex’ (trellised)