the root of it

This year’s Thanksgiving dinner was something to write home about.  A menagerie of vegetable dishes flanked my mother’s heavenly, rosemary-infused turkey: roasted bliss potatoes, braised fennel, sautéed Brussels sprouts, butternut squash soufflé.  But the one side that got me thinking was the roasted rainbow carrots.

I grew these carrots from seed in my backyard garden.  The colorful crop produced tall greens and long, spindly tap roots that plunged into the soil below the raised bed in which the carrots grew.  But what about root crops that don’t have the luxury of growing endlessly downward?  As depth-limited environments with thin soil profiles, rooftop farms and gardens present a unique set of challenges.  Thankfully, we can pluck some useful knowledge from the green roofing world.

For decades, green roof designers have experimented with growing deep-rooted plants – even trees! – on rooftops.  The key is selecting hardy cultivars, providing at least the minimum thickness of soil in which the plants can survive, and ensuring that their nutritional needs are met.  Irrigation is also key in cultivating plants in depth-limited environments.  Proper irrigation techniques often allow deep-rooted plants, like ornamental grasses, to flourish in unusually thin soil profiles.

In the case of rooftop carrots and other root crops, follow these 6 steps:

1| Make sure your roof contains adequate root protection (i.e. a polyethylene or polyvinyl chloride root barrier)

2| Select hardy cultivars that won’t grow excessively deep

3| Blend or purchase well-drained growth media

4| Mound enough media for each crop

5| Pay close attention to each crop’s nutritional needs

6| Provide sufficient drip irrigation

What’s been your experience with root crops?  Have you tried growing them in a container or other depth-limited environment?  We want to hear all about it!