Lilac

What’s blooming in the area: Tamarix, snowball, yucca, Austrian Copper and pink shrub roses, golden spur columbine, fern-leaf globemallow, white evening primrose, stickseed whitebristle, oxalis, bindweed, native and common dandelion, goatsbeard, hoary cress; tansy, tumble and purple mustard; rice, needle, downy chess, and three awn grass; June grass going to seed.

What’s blooming in my garden, looking north: Perky Sue; buds on fern-leaf yarrow and blanket flower; butterfly weed emerged; fruit developing on sour cherry.

Looking east: Siberian pea shrub, coral bells, thrift, pinks, small-leaf soapwort, snow-in-summer, pink evening primrose, Mount Atlas daisy; buds on peony, pink salvia, creeping baby’s breath, Kellerer yarrow; last year’s sunflowers coming up.

Looking south: Spirea, lilac; buds on beauty bush.

Looking west: Tulip, iris, flax; buds on sea lavender; fruit forming on peach.

Bedding plants: Sweet alyssum, snapdragons, Dahlberg daisy.

Inside: Aptenia, kalanchoë, zonal geranium

Animal sightings: Rabbit prospecting; ladybug, bumblebee on pinks, large black butterfly, darning needles.

Weather: New moon; cold temperatures killed leaves on locust Tuesday; rain mid-week, but winds returned even on hot afternoons.

Weekly update: Lilacs like a cold spring, or so I was told by neighbors when I lived in Wyandotte County, Ohio, the year newly flushed flowers filled the town with their fragrance.

This apparently is more than folk wisdom. Remains of common lilac’s progenitor appear in Hungarian fossils from the tertiary, and, according to Kim and Jansen, the shrub probably evolved 12 million years ago when ice-caps were developing. Glaciers may have isolated it from its Oleaceae peers in Asia.

Joseph Caprio determined common lilacs still need 1049 hours between 37 and 48 degrees to set their buds. Those minimum 44 days represent a few more chilling units than apples require, which may explain why they emerged about four days after the orchards this year.

Temperature is such a strong factor governing Syringa vulgaris that scientists have been using it to evaluate the effects of changes in climatic conditions. When they were establishing a baseline, Caprio’s colleagues discovered lilacs were unfolding an average 7.5 days earlier in the western United States in 1994 than in 1957. Peter Marra’s team found the date for bud burst was 3 days earlier for every degree of increased average temperature in the east between 1961 and 2000.

This year, we had a snowy winter, followed by warm temperatures in mid-March. My first florets opened April 25. I planted the shrub in 1997 and it first blossomed two years later. The earliest date the racemes appeared was last year on April 21; the latest was in 1999 on May 10. A twenty day fluctuation is not unusual.

Lilacs may demand cold weather, but they did not like last weekend’s cold winds and frosty mornings. My lilac was in full fluorescence Friday, but has had only scattered, four-petaled trumpets since. Towards town Monday, there was only one white lilac left with much color. Revenants of light lavender remained in 15 yards; some white sprays remained in two places and two people had dark purple heads.

The affinity between lilacs and cold is obviously conditional. Last year a man down the road watered his shrubs when morning temperatures were still low enough to freeze. This year, those are the only shrubs I don’t see with even a hint of leaves. I don’t know if the iced branches, the prior year’s grasshoppers, or something else killed them, but established lilacs don’t die willingly: they might have lived another hundred years and pirouetted through most of them.

Notes:
Caprio, Joseph M. "Flowering Dates, Potential Evapotranspiration and Water Use Efficiency of Syringa vulgaris L. at Different Elevations in the Western United States of America," Agricultural and Forest Meteorology 63:55-71:1993.

Cayan, Daniel R., Susan A. Kammerdiener, Michael D. Dettinger, Joseph M. Caprio, and David H. Peterson. "Changes in the Onset of Spring in the Western United States," American Meterological Society Bulletin 82:399-415:2001.

Kim, Ki-Joong and Robert K. Jansen. "A Chloroplast DNA Phylogeny of Lilacs (Syringa, Oleaceae): Plastome Groups Show a Strong Correlation with Crossing Groups," American Journal of Botany 85:1338-1351:1998.

Marra, Peter P., Charles M. Francis, Robert S. Mulvihill and Frank R. Moore, "The Influence of Climate on the Timing and Rate of Spring Bird Migration," Oecologia 142:307-315:2005.

Photograph: Common lilac, 12 May 2007, after cold temperatures killed most of the flowers.