Lilac Cues
by Michael Hofferber. Copyright © 1999. All rights reserved.

Fastened to our refrigerator door with a cow-shaped magnet is a fading piece of print clipped from some newspaper or almanac long ago. The clipping has outlived at least three refrigerators and survived several moves, traveling with us like some heirloom we dare not misplace.

Though curled at the edges and smeared a bit, the words are still legible:

     "When the first leaves of the lilac appear... plant peas, potatoes, lettuce, radishes and the like.
     "When the first lilac blossoms appear... plant beets, carrots, kohlrabi and other cole crops.
     "When lilac blossoms reach full bloom... plant beans, corn, cucumbers and squashes.
     "When the lilac blossoms fade and fall... the danger of frost is probably past and it's time to set out tomatoes, peppers and other warm-weather crops."

These tips, which have served as our planting calendar for many years, come from phenology, the study of biological phenomena and their happy coincidences. Farmers and gardeners have been noticing and recording phenological relationships as folklore for ages.

I keep a file marked "Phenology" in which I collect aphorisms the way some folks collect stamps. Some are pieces of poetry or proverbs. Others are more like rules of
thumb. Here's a few examples:

     When oak leaves are the size of a mouse's ear... set out tomato,
eggplant and pepper plants.

     When new oak leaves are the size of a squirrel's ear... look for morels.

     A wet, cold May? A barn full of hay.

     If owls screech in foul weather, it will turn to fair.

     Fish spawn when dogwood is in bloom.

     Catch your fish when rain is in sight.

     Rains are very near when toadstools suddenly appear.

     The danger of frost is past when white clover blooms.

     A swarm of bees in May is worth a load of hay.

These may seem like superstitions, but there's a lot of scientifically verifiable information backing up our folklore. Phenology is the study of temperature, moisture, and day length. It assists in management of garden pests. In the case of insect pests, their survival depends upon synchronization of their life cycles with the life cycle of their food source. By keeping track of growth stages of plants (for example, when the plant flowers), we can reliably predict when certain plant pests may occur.

Phenology is one of the cornerstones of Integrated Pest Management, for example, which employs "plant phenology indicators" in timing applications of various agents to control insects and disease. Rather than relying on general calendar dates, phenology automatically adjusts for the natural variations of weather. This knowledge allows us to control insect pests when they are most vulnerable. In the field, it's much easier to notice that the forsythia is blooming than it is to calculate "growing degree days."

In my own garden, it might be more scientific to use a soil thermometer and meteorological forecasts before setting out tomatoes, but lilac blossoms are more elegant.

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