Sunday, May 04, 2008

Siberian Pea Tree

What’s blooming in the area: First lilacs, wisteria, iris, flax, tansy mustard, hoary cress, western stickseed, common and native dandelions, cheat grass. June grass is beginning to unsheath, first tahokia daisies are coming up, Virginia creeper and grape are starting to leaf out.

In my yard: Siberian pea tree, tulips, daffodils, grape hyacinth, yellow alyssum, mossy phlox, Mount Atlas daisy. Perky Sue has buds, while forsythia and sand cherries are leafing out.

Inside: Aptenia, kalanchoë; bougainvillea buds.

Animal sightings: More horses in to pasture.

Weather: Another week with temperatures ranging from the low 30's to the mid 70's that encourage plants to grow so high winds can suck the moisture from the soil, the stems and the leaves, leaving a false promise of fertility that was the talk of people in line in the post office yesterday. Forest fire danger is high with the last snow April 4 and the last significant moisture March 5. 14:44 hours of daylight today.

Weekly update: My Siberian pea tree reminds me that nature, like any good choreographer or composer, likes to take a motif and run it through all the possible positions or keys and tempos.

With Caragana aborescens, the theme is the archetypical pea flower with two lips, one hunched over the other that we’re used to seeing in red, pink and white on perennial sweet pea vines or in more varied colors on knee-high annuals. Nature tried clusters of large cream disks hanging off high branches with the catalpa tree and short spikes of tiny purple funnels for loco weed.

On this particular legume, nature spaces small, narrow flowers between clover pads so they look like dead leaves from a distance. The blossoms are so short lived that after the first few day, the shrub doesn’t look much better up close when buds and dead flowers outnumber the fully flexed ones. The narrow brown seed pods look more natural when they reach out from the limbs in late summer.

Obviously, humans don’t share nature’s fascination with the arabesque and want something more from a plant than a demonstration of what’s possible, no matter how grotesque. I bought three bare roots from an Ohio nursery in 2001 because, much as I like forsythia, I don’t like it near the pink and white flowering trees in spring and wanted another yellow to add depth to the arching branches.

Unfortunately, last year was the only year the two floral periods overlapped. Most years the pea tree starts to bloom the day after the last forsythia flower withers. This year, frost killed the one before the other could open.

In spring the bright chartreuse forsythia foliage clashes with the greyed lime-green of the pea tree. The smooth, yellow-brown bark of the one jars against the olive ridged bark of the other. However, by summer, the leaves darken on both and expand to produce the variations in color and form I’d hoped for in spring.

Most who plant Caragana do so for utilitarian reasons. On the northern great plains, the USDA suggests farmers use rows of trees and shrubs to protect their fields from drying winds. When extension experts draw up lists of survival requirements, they discover few densely-branched, long-lived, quick-growing plants can handle cold winters, high winds, and saline soils while surviving grasshoppers, repelling gophers, and tolerating modern pesticides and herbicides.

They’d also like the roots to be porous and the plants to be natives that will never escape, but they can’t have everything. They accept the pea tree for the outer edge of tree rows, where the numerous 12' vertical branches create barriers beneath the taller tree crowns.

Botanists know grasshoppers will eat pea trees bare and heat can defoliate them, but they also know the shrubs recover in fall to return fully clad the following year. They also appreciate the dense roots that reach down 16" to hold the soil and attract rhizobia bacteria to add nitrogen.

Siberian pea trees grow on the steppes of Asia from the countries bordering the Silk Road, Uzbekistan, Tajikstan, Kyrgystan, and Kazakstan, north to Siberia and Mongolia and west to Ukraine, Belarus, and the Balkans. Wayside says the Russian Imperial Botanical Gardens received a sample in 1730, and Lamarck knew about it in 1785, either from the Jardin du Roi or from his travels through Europe in 1871 and 1782 as Louis XVI’s royal botanist. They came to the United States as ornamental shrubs do, with little fanfare, but weren’t much used until the 1930's when the Soil Conservation Service promoted them.

Even though pea trees generally don’t grow well south of Nebraska, they do adapt to New Mexico. The New Mexico Botanist reports some have seeded themselves into a sandy wash near the Las Dos subdivision northwest of Santa Fe. Like anything that can survive this hostile environment, they introduce unexpected variations into the garden and, sometimes, to the consternation of environmentalists, into the wild where nature remains an inveterate experimenter with form oblivious to human aesthetics.

Lamarck, Jean Baptiste. Encyclopedie Methodique. Botanique 1:615:1785.

New Mexico State University, Range Science Herbarium. "Plant Distribution Reports," The New Mexico Botanist, 19 October 2004.

Wayside Gardens. "Caragana 'Walker'" catalog description available on-line.

Photograph: Siberian pea tree, 27 April 2008.

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