Overwintering Perennial Herbs
Protecting Valuable Herbs Beyond Their Comfort Zones
Several of the most valuable herbs are perennials that aren't reliably hardy in Zone 5 and colder, particularly without good snow cover. Growing them under row cover in an unheated hoophouse or high tunnel can keep them alive through severe cold.
Farmers at a small farm in Berkshire, New York, showed this in a project funded by a Sustainable Agriculture Research and Education (SARE) grant to study overwintering perennial herbs.
They built an unheated 30' x 96' greenhouse covered with inflated double poly, planted in-ground beds, and used a data logger to track temperatures outside, inside, and beneath row cover held up on wire hoops.
The area falls in Hardiness Zones 5a, 5b, and 6a. That winter the coldest outdoor reading was -22.3°F (-30.2°C). At the same time it was 3.2°F (-16°C) inside the unheated hoophouse, 14.9°F (-9.5°C) under the row cover, and 33.1°F (0.6°C) in the soil.
Herbs in the trial included rosemary 'Arp' and lavender 'Lady' and 'Hidcote', plus French tarragon, purple sage; pineapple mint; oregano, and lemon thyme.
After trying both straw mulch and row cover, they found row cover alone worked best; mulched plants were more prone to mold and recovered more slowly in spring. With a single layer of Agribon+ AG-19 on wire hoops over the beds, nearly all of their herbs survived the winter, allowing them to take cuttings for plant sales and sell fresh-cut herbs from April into December.
Founder of Growing for Market magazine
She and her family have grown vegetables and cut flowers in Kansas since the late 1980s, selling through CSAs, farmers' markets, restaurants, grocers and florists.
Her books on market farming include The Flower Farmer and The Hoophouse Handbook.
