In early fall, the Eagle Street Rooftop Farm's vegetables are on cruise control. The blue-green rows of kale stand like palm trees, their leaves picked but for the highest, newest growth. Hot peppers hang off their green parent plants like sunset-colored Christmas ornaments. Every fruit on the farm—eggplants, tomatoes—seems to sense the coming frost and begins to sprint into production. The harvest seems endless. The days pass like waves of fever: cold in the morning, hot in the afternoon, cool again at night.
When I was growing up in Chicago, the transition between August and September marked the end of lifeguarding season on Lake Michigan. It was a glorious month, and I was nostalgic even before it ended. Since I shifted to New York's vegetable-growing calendar six years ago, August has become the month in which (sunburned, exhausted, wasted by the long work days leading into the summer solstice) I snap. For this, I savor September. I begin to talk about the fall with the same glint in my eye that teachers get when they know the winter holidays are coming up.
The changing season shifts our work on the farm into a pattern of storage. Under September's full moon, with the Manhattan skyline glittering across the East River, we stuffed jars with a simple salt-and-vinegar brine, hot peppers, and green tomatoes. Our herbs hang to dry in the second floor of the Rooftop Farm warehouse. The farm's animals notice the shift into fall, too. As their pollen sources change, the bees' honey begins to turn a darker, richer amber. The chickens begin to molt, their feathers scattered around the coop like post-pillow-fight debris.
Since the Rooftop Farm's beds are too shallow (four to six inches deep) to successfully grow winter squash and other fall staples, we use the available space and the last nights of warm summer soil to plant thousands of spinach seeds. The few weeks before late October's frost help the spinach (particularly good hearty varieties like Bloomsdale) establish its roots before it gets hit with snow, when it dies back until the first warm weeks of April. Because we planned ahead, we will get an easy early springtime crop as we start planting our first new pea, radish, and lettuce seeds. Plus, the green roof stays green all winter with the spinach around.
In whatever space isn't covered in spinach, kale plants, or annual herbs, we sow cover crops: clover and hairy vetch. Cover crops are the yellow traffic light of farming, keeping the land active while it's not in full agricultural production. This year, trying to get the most bang for our buck-per-square-foot, we even added radish seeds into the mix. When the radishes are harvested (roots and all) a month after planting, the cover crops will continue to grow. With this intercropping, we'll get successful food (spicy "French Breakfast" and rarer purple radishes) while building healthy soil.
Although farmers use a range of plants (edible or not) for cover crops, for the Rooftop Farm I chose the clover and hairy vetch because, when weeded out, vetch and clover both make great greens to maintain the brown-and-green carbon to nitrogen balance of compost piles. Unlike other cover crops such as rye or winter wheat, which can take most of the following summer to mature, clover and vetch can be planted in the fall, last the winter, and don't have to grow much past early May to be useful. Come spring and summer, we need that time and space to grow our vegetables. On most farms, you'd leave a field or two to lie fallow each season. On our rooftop, a fifth of an acre, we haven't the luxury to pause.
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Best of all, clover and hairy vetch are legumes. Like soybeans, peanuts, and beans, their roots can host a type of bacteria that fixes a nutrient present in the air all around us: nitrogen. If you've ever noticed the beautiful verdant glow of trees after a good dose of rain and lightning, it's because their leaves actually are greener, charged with the rush of atmospheric nitrogen that comes zapping down with every storm.
In healthy soil, the roots of leguminous crops are covered in what looks like tiny clusters of white grapes. In our first year at the farm, barely any of our legumes hosted the bacteria—rhizobia—because the soil was a new and fairly sterile ecosystem. At the end of this spring, when we pulled our peas, I shrieked with joy (oh yes, like a schoolgirl) when their roots came up colonized. I pushed the produce under each apprentice's nose, the rhizobia on the roots like an artfully strung necklace of pearls. A farmer's best investment is healthy soil, and with the entrance of great bacteria into our landscape, we were on our way toward good, sky-high dirt.
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