sky-high winter greens

While rooftop farms around the country lay fallow for winter, one skyline gem continues to churn out greens.  Noble Rot, a restaurant and wine bar in Portland, OR, supports a 3,000 square foot (0.07 acre) farm that fuels the kitchen below.  The upscale restaurant occupies the sixth floor of a LEED Platinum building, providing a panoramic view of the city.

I travelled from snowy Philadelphia to the City of Roses last week, and saw for myself how crops continue to grow – albeit slowly – in Portland’s mild winter climate.  Kale, lettuce, endive, cabbage, arugula, parsley, thyme, and garlic sprouted from the roof’s raised beds and steel containers.  A fig tree with small buds stood near the roof’s bee hive and compost bins, and to my surprise, restaurant co-owner and manager Kimberly Bernosky explained that the tree remains uncovered year-round.

How do the growers at Noble Rot keep their crops warm in winter?  Fig tree aside, they elicit the help of insulated containers.  The steel containers were wrapped in a thin layer of insulation, which helps to moderate soil temperature fluctuations.  Several of the steel containers were additionally retrofit with opaque lids – resulting in vessels known as cold frames – in order to retain heat from the sun.  By trapping solar radiation, cold frames act like miniature greenhouses and moderate or warm both soil and air temperatures.

A handful of the farm’s raised beds were covered with plastic to keep the greens inside toasty.  Ground-level farmers and gardeners often use plastic or garden fabric to cover crop rows or raised beds, but on a roof, the wind may blow the covers off your crops!  Noble Rot keeps their plastic in place with the help of wire framing, attached the the wooden raised beds.  These low-stature “hoop houses” prevent air temperatures above the greens from swinging down to uncomfortably chilly levels at night.  A rather clever approach to crop warming.

Of course, Portland is blessed with a relatively mild climate that allows for year-round production.  Farmers in less utopic regions (like the Northeastern US or Canada) may not be able to grow throughout the whole year, but they sure can extend their growing seasons by expanding upon Noble Rot’s clever innovations.  What tricks do you use to keep your crops warm?