When to plant bulbs in the fall? Science, nature offer some clues

To ensure that bulbs planted in the fall will bloom in early spring, timing is important.

Plant too soon, and the bulbs might rot in rain-saturated ground. Plant too late, and they won't have time to build enough energy for flowering.

A soil thermometer is a more accurate tool than a calendar. The best time to plant bulbs varies according to where you live and what the weather has been like approaching autumn.

Fall seasonal benchmarks are being questioned, however, with winters seemingly becoming shorter, said Debby Horwitz, a horticulturist with American Gardens, a landscape, architecture and construction firm in Elmhurst, Illinois.

"It used to snow in the Chicago area in November when I was a kid," Horwitz said. "That hasn't happened here in a long time. If you get ahold of any bulbs in December, go ahead and plant them."

Bulbs perform best when planted in soils that have cooled to 55 degrees or lower. Horticulturists recommend that you plant them in holes three times the height of the bulbs deep.

"Sometimes the (planting) rules don't matter," said Mark Konlock, director of horticulture for the Green Bay (Wisconsin) Botanical Garden. "You can dig a big hole and simply chuck them in there. You don't even have to put them right side up. Gardening with bulbs is easier than you might think."

The most popular bulbs for fall planting include daffodils, crocus, snowdrop, hyacinth, tulips, scilla, fritillaria, allium, irises and gladiolus.

"It's always best to do it at the appropriate time," said Tim Schipper, founder and owner of Colorblends, a wholesale bulb company in Bridgeport, Connecticut. "The more chilling they get, the better the quality of the bloom and the longer their stem length."

Refrigerate bulbs for a time before planting if you live in the South, he said. "Everywhere else, it's plant whenever you feel winter coming on."

By that, he means taking your fall planting cues from nature. Here are some natural markers gathered from Colorblends customers who contend it's time to place bulbs in the ground when:

- Fall leaf colors have moved just past peak.

- Squirrels are digging in acorns as fast as they can.

- Birds are flocking up for their southward migration.

- You begin smelling wood smoke from neighborhood stoves and fireplaces.

- You start turning on the heater in your car.

- Your kids start asking for gloves, or you wake in the middle of the night suddenly needing a blanket.

"One of the benchmarks that works best for me is when I see frost on the windshield," Schipper said. "I also pay attention to the fall foliage, to the hostas when they lay down, and I follow the crickets. It's time to plant when they become quiet and they can barely get their violins going."

Whatever the timing, bulbs are capable of taking a great amount of abuse, Horwitz said.

"We've planted daffodils in ground frozen solid," she said. "One of our guys cut through the earth with a pick axe while I placed the poor little things in the ground and covered them the best I could with clumps of frozen dirt.

"It was December. They came up great the next spring."