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Colorado winters tough on biennials

Robert Cox, Special To The Rocky

Published January 27, 2007 at midnight

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Question: I'm ordering vegetable-garden seeds now but wondered where seeds from carrots, cabbage and beets come from. I've never seen these plants develop seed heads.

Answer: There are several vegetable-garden plants that are biennials. Biennial plants produce leaves and store carbohydrates the first year from seed. They overwinter and then, drawing on stored carbohydrates, produce flowers and seed during their second year. Biennials die after producing seed. Since many biennials can't overwinter in Colorado due to cold and dryness, we don't see them produce seed. Additionally, we usually harvest them for their edible portion during their first year. Beets, cabbage, carrots, cauliflower, celery, kale, kohlrabi, leeks, onions, rutabagas, Swiss chard and turnips are examples of biennials grown in the vegetable garden. Seed-production areas for many of these crops are in states where winters aren't as cold and dry.

Q: What is a chipotle?

A: The term (chih POTE lay) usually refers to a dried and smoked jalapeño pepper or another thick-meated variety of chile pepper that's been smoked to preserve it. They're left on the plant for as long as possible, maturing to a deep red color. When the peppers have dried on the plant, they're picked and moved to a closed smoking chamber, where they're spread on metal grills and wood-smoked to become chipotles.

Q: Why don't trees grow above timberline?

A: While there are other factors, it's mostly related to coldest temperatures in winter. Most cold-hardy trees can inhibit ice-crystal formation in their cells (which would cause cell death) at temperatures far below freezing. The approximate limit to this ability is minus 40 degrees. Timberline is that variable elevation above which coldest winter temperatures may fall below the minus-40-degree mark.

This is why timberline elevations increase as you go south. For example, timberline in Alaska is about 4,000 feet, 8,000 feet in Montana, 10,000 feet in Wyoming, 10,500 feet in Colorado and 11,000 feet in New Mexico and Arizona. Low-growing shrubs near or above timberline are usually covered by snow, an effective insulator, during most of the winter.

Robert Cox is the Colorado State University Cooperative Extension horticulture agent in Arapahoe County. For information on many horticulture topics, visit www.planttalk.org.