The garden plots at the UpGarden P-Patch on top of the Mercer St. Garage near the Seattle Center. photo/Hallie Golden

The garden plots at the UpGarden P-Patch on top of the Mercer St. Garage near the Seattle Center. photo/Hallie Golden

The roof of the Mercer Garage, near the Seattle Center, was built to hold cars, but what about piles of dirt?

When landscape architects Eric Higbee and Nicole Kistler teamed up with the city’s P-Patch Community Gardening Program to design the country’s first large-scale rooftop garden, that was one of the logistical issues they had to work out. They determined that the garage, which was built for the World’s Fair back in 1969, was made to hold 40 pounds per square foot — a weight limit that was more than enough for cars, but 60 pounds less than needed for saturated soil.

“The structural weight limit is the biggest issue,” Higbee explained. “If you were to just take soil and spread it across the garage, it would only be about 8 inches.”

The architects were able to get the garage to hold 12 to 18 inches of soil by using a method of weight balance. They focused the dirt in broad terraces, which were split up by walkways. This way, they could have a deeper supply of dirt — just not in every square foot of the roof.

Intensive rooftop gardens (ones that produce crops) are becoming more popular across the country, through the movement for sustainable food. In Seattle, as with many big cities, they have become especially popular because there are so few spaces available for gardens on the ground level.

“In the city, it’s harder to find land to garden, and there’s a lot of demand, so we try to find a creative solution,” said Department of Neighborhoods community-garden coordinator Sandy Pernitz.

But creating these rooftop gardens isn’t quite as easy as simply laying down dirt and planting seeds. It takes some real planning, especially on top of the average house.

Colin McCrate, an urban agricultural specialist with Seattle Urban Farm Co., explained that this popularity has sprouted out of the trend for the green roof, a type of roof that has a positive environmental impact, by adding insulation and absorbing rain, but is not for the purpose of producing food.

“[An intensive rooftop garden is] like energy-efficient lighting: It’s a new technological idea, which has proven results, so people start accepting it and using it more and more,” McCrate said. “Every year, from our experience, more and more people are interested in it.”


Holding its weight

McCrate was one of the people who helped design and implement the garden of top of Bastille Café & Bar in Ballard. It was established in June 2009 and is the first and only “productive” rooftop farm in Seattle. 

Most of the 1,200 square feet of planting space is home to plants like lettuce, arugula, parsley and basil — all for the chefs to harvest and put in the restaurant’s food.

Seattle Urban Farm Co. had been trying to promote this rooftop-garden idea to other restaurants, but it was “not the sort of thing you can quickly talk people into,” McCrate said. The owners of Bastille had independently come up with the idea, and they were directed to the Seattle Urban Farm Co.

The company is in the process of getting another rooftop garden built on top of a mixed-use building in the Eastlake neighborhood, for the two restaurants on the bottom floor: Sushi Kappo Tamura and Ravish. Right now, the building has green roof space for plants and capturing rainwater, so the company plans to simply repurpose the space to produce food. 

He said the rooftop garden atop Bastille works well because the building it was moving into was 100 years old. And “when they decided to start the restaurant, they had to do all this structural work anyways, so they just decided to do this extra work to put the garden on top,” McCrate said.

But if someone is not already planning on doing a lot of structural work, building a productive rooftop garden can get expensive. McCrate explained that, about three years ago, people started thinking it was a great idea, but no one wanted to actually create one because most structures would need to be fortified so that they can hold the weight of the soil. 

No structural changes were necessary for the garden on top of the Mercer Garage, but planners did run into other issues. Since the dirt on a roof is in such direct sunlight, they needed a good irrigation system for keeping the soil moist. 

They also had some difficulty getting everything they needed up to the roof and, at one point, had to spend money on a crane. 

These challenges made the garden take longer to create than originally anticipated. They had hoped to be finished with it back in April, but it wasn’t officially opened until June 2.


A garden to feed on

Craig Moore, who lives in a condo in Queen Anne, was one of the volunteers on the project and now has one of its 110 vegetable garden plots. Between him and his wife, they put in 260 hours of work, the most of any other volunteers.

“None of the local P-Patches are close to us,” Moore said. “We walk everywhere, so we were looking for a place to garden where we could walk to.”

Since they got a late start in the vegetable-planting season, and because the project wasn’t completed until June, the couple used mostly starter plants instead of seeds. Moore said he wants fresh vegetables for him, his wife and 2-year-old daughter to eat.

So far, they’ve planted snap peas, snow peas, broccoli, basil, cucumber and, most importantly, tomatoes.

He explained it’s the tomatoes that his family talks about wanting to grow, since they consider them far superior to the ones available at the grocery store.