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To have a garden on the roof

Last Updated 18 June 2015, 14:10 IST

Anne Raver explores the world of urban gardening with Kerry Trueman and Matt Rosenberg, as the couple gives tips on how to start your own roof garden

Kerry Trueman and Matt Rosenberg began growing tomatoes on the roof of their third-floor walk-up in the West Village more than 20 years ago. “We didn’t know anything - we used Miracle-Gro,” said Kerry, 54, who blogs about the politics of food and writes about climate change.

“But it changed the way I viewed things in cities. Whenever I was on a high floor, looking down, I would see all this roof space and say: ‘Wow, you could grow so much.’ There are no woodchucks or deer, no Japanese beetles. And so many things grow so well in containers.”

Using a ladder to climb through the roof hatch, they grew many things on their roof - strawberries, 20 different roses, blueberries, corn and hops. They had to dismantle the roof garden in 1998 during a legal battle to keep their building rent stabilised. But by then, they were hooked. “Tomatoes are the gateway drug,” Kerry said.

These days, their garden reincarnation reside in boxes that face south, east and north outside the windows of that same 450-square-foot apartment. At 4 1/2 feet long by 1 1/2 feet wide and deep, the containers are almost too big to call window boxes. “Matt calls them coffins,” Kerry said.

Made of rot-resistant cedar, the boxes are held snugly to the walls by heavy-duty steel brackets, the kind used to keep air conditioners from falling to the ground. 

Wooden slats are spaced slightly apart at the bottom, for drainage. And unlike coffins or traditional window boxes, they have only three sides. The open side faces into their apartment, so that plants growing in malleable bags, called root pouches, can be easily moved in and out.

“I play musical chairs with them,” said Kerry, holding up an empty 10-gallon bag with a wide double-stitched handle. “They come in all different sizes. You can grow herbs in the one-gallon pouch. And they’re made of recycled plastic water bottles.”

If the haricots verts are shading out the Ichiban eggplants, or the arugula has gone to seed and it’s time to put in the Sun Gold cherry tomato plant, no problem. At the end of the season, the bags can be washed, folded and stored in a city-size closet.

Giving them what they need

They are evidence that urban gardening is a lot easier now than it was 20 years ago, when Kerry would lug 20-pound bags of peat moss and mushroom soil uptown from the Smith & Hawken on Broadway in SoHo.

Now she uses lightweight compressed bricks, which expand into 10 quarts of potting soil when mixed with water. “I combine them with compost and a little perlite,” Kerry said.

If she is growing flowers or fruit like alpine strawberries or eggplants, she mixes in a little Peruvian bat guano, which is rich in phosphate and potassium. If she is growing dwarf blueberries, which need acid soil, she adds a bit of Holly-tone.


To protect plants from becoming waterlogged during a heavy rain, better than rocks, another recycled plastic material, can be layered into the bottom of a root pouch, or any container, to avoid anaerobic conditions. Conversely, to help soil retain moisture on hot, dry days, Kerry sprinkles in a few water-absorbing crystals like terra sorb, which take up 200 times their weight in water.

Another recycled plastic product, rain-mat, which is infused with its own absorbent crystals, can be cut to size and sandwiched between layers of soil to create a reservoir. “I put a rain-mat about an inch below where the roots of my seedlings are going to end up after they have established themselves,” she said. Plant roots are then encouraged to grow downward, seeking water. And deeper roots mean more heat and drought-resistant plants.

Kerry, who used to be a decorative painter before she tore a knee ligament muscling some file cabinets up the stairs, calls herself a botanical bricoleur. She cuts up birch branches to make crown moldings and makes trellises out of bamboo and yarn. She encourages people who think their apartments are too dark to grow plants to pick up a mushroom-growing kit. And maybe one of those hayracks.

“It’s an entry point,” she said. “We can never grow all our own food in the city, but even getting people connected to one window box connects them to the natural world.”

Getting the basics right

* Assess light conditions. Tomatoes, eggplants and peppers need six to eight hours of direct sun; Asian greens, loose-leaf lettuces, mints, basil, parsley and other herbs flourish in part shade and as little as three hours of sun.

* Vary the pots to suit the plants: leafy greens, herbs and cherry tomatoes or hot peppers can grow in smaller one to three gallon containers; a full-size tomato or eggplant does better in a four to five gallon container.

* Use a fertile, light potting mix rather than garden soil, which is heavy and may contain weed seeds or disease. A ratio of half compost, half soilless mix works well.

* Water daily or even twice a day, depending on exposure to sun and wind. Do not let plants dry out, which will stunt growth. Place pots on saucers, to hold a bit of water. Use water-retaining polymers, sparingly, to increase moisture.

* Self-watering pots with reservoirs are helpful. Drip emitters, or “spaghetti” lines can be set into pots and set on a timer, if you have a number of pots on a terrace or roof.

* Conversely, watering by hand is the best way to check on how each plant is growing. Water deeply, at the base of the plants.

* But don’t let plants get waterlogged, either. Check after a heavy rain to make sure pots are not standing in water, which creates anaerobic conditions.

* Fertilise every other week with organic fish or seaweed emulsion, which is mixed with water. (Half strength is usually best.)

* Herbs, tomatoes, blueberries, nasturtiums and many other edibles can flourish in window boxes, pots, hanging baskets and recycled containers.
* The only limitation is our imagination and willingness to experiment. Remember: Every good gardener has killed many plants along the learning curve. 

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(Published 18 June 2015, 14:10 IST)

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