Volume 15, Issue 2 ~ January 11 - January 17, 2007

The Bay Gardener

By Dr. Frank Gouin

Warm Winter Weather’s Chilly Harvest

Plants need cold now if they’re to grow come spring

With temperatures in the 50s and 60s, our unseasonable weather has meant more comfortable time outside. But our mild fall and early winter concerns home gardeners and commercial nurserymen. The warm weather forces plants into growth during winter months.

Native plants have certain cold requirements to remain healthy and full. Peach and apple flower buds, for example, must endure some 650 to 850 accumulative hours of temperatures between 40 and 32 degrees before they can flower.

Vegetative buds that produce leaves and twigs require nearly 1,000 hours of accumulative cold before growing. Plants must go through these cold temperature periods or they will remain dormant. Any growth initiated will be abnormal; only a few of the buds will grow.

In addition to cold temperature requirements in winter, plants have specific light demands. As the daylight hours lengthen in spring, plants grow faster. As daylight hours shorten in fall, plant growth decelerates. Plants grow more during warm days and warm nights, slowing during periods of warm days and cool nights. Our native plants do not grow well in winter, when temperatures remain constantly cool.

Native plants have survived in our environment for thousands of years and will continue to survive long after we are gone. Global warming may allow species to extend their growing range north. Some southern species — which wouldn’t have survived here in years past — can now tolerate our region.

Remember, though, that it only takes one severe winter to wipe out those species, because they lack winter hardiness genes. Such species, like gardenia, yaupon holly, bougainvillaea and more, might not survive a harsh winter, so they’re a poor landscape investment for Maryland gardeners.

Ask Dr. Gouin your questions at frgouin@erols.com. All questions will appear in Bay Weekly. Please include your name and address.

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