Siberian Pea Tree Autopsy

Weather: Sun angles are changing; the sun was in my eyes when I was sitting at my desk for the first time this year on Monday. The zonal geraniums on the indoor porch are happier than I; they all are in full bloom.

Last useful rain: 3/11. Week’s low: 23 degrees F. Week’s high: 72 degrees F in the shade.

What’s reviving: Hollyhocks, sweet peas, golden spur columbine, chrysanthemums, brome grass; arborvitae have greened; fern bushes have leafed

What’s coming up: Garlic chives, Queen Anne’s lace, oriental poppies, larkspur seedlings, alfalfa, white yarrow

Tasks: Finished the difficult work on the wall I built to stop soil from eroding into the path of my gate, and keeping it from opening when the ground heaves in winter.

Animal sightings: Small birds. When I was digging out soil for the lower course of the wall, I uncovered an active caterpillar and a grub. Heard geese honking near the river on Monday.

Weekly update: High winds returned Wednesday. Friday night they took down one of the Siberian pea trees. When I looked, one of the stems had no roots and one had a few laterals that tore before they broke.

The trees grow like shrubs here. This one was about 8' high and 5' across, with two main stems. I pulled the interlaced branches apart, and loaded the smaller one onto the wheelbarrow to take to the burn pile. The other was larger and heavier. It took some effort to get it to balance diagonally across a dolly.

Then I looked at the roots. There were none on the smaller stem. The larger one had a few laterals that had torn, and a few tiny ones I had to cut. I pushed them back into the hole and covered them, hoping they would resprout.

When I tried to discover what type of roots the species had, I ran into the usual problems that no one looks, and everyone copies Wikipedia without attribution. All the it said was the root system was extensive, but not how wide or how deep. [1]

My first thought was the ground squirrel, but there was no tunnel. Besides that animal seems to feed on members of the rose family, and Caragana arborescens is a legume.

The second possibility was some kind of root rot. The trees are native to Siberia and Manchuria, [2] but researchers did not include Siberia pea trees in their list of Russian trees affected by fungal diseases. [3]

The question remains what happened. The species is used for windbreaks on the northern plains. [4] The high winds of last week and the snow load in February should not have been a problem.

Canadians indicated Caragana arborescens normally lives for fifty years. [5] This tree was planted as a bare root along with two others in 2001. They are about 18-years-old, so it didn’t die of old age.

The Canadians also suggested the pea trees were "very drought tolerant" but would "not tolerate prolonged flooding." [6]

Last summer was hotter than usual. That amplified the effects of the lack of rain. The first of July I noticed this particular shrub was losing leaves.

Last year was also the time I replaced some soaker hoses that, at the best of times, supplied water in 3" strips with sprayer hoses that provided more water over a wider area. When I was fighting with the older hoses, I had snaked one around the base of this particular tree when I looped it back on both sides of the others. That may have caused the roots to be concentrated in a small area. They then may not have been able to respond to the change in water distribution when it got hot.

When I saw the leaves dropping, which is a normal response of the species to drought, [7] I shifted the hose a bit to make sure it got more water. Maybe I was flooding it instead of starving it. The lack of roots is consistent with too much water.

So it may have been victim of the classic conundrum: is it too little or too much, and did compensating for the one cause the other? Killed with loving care, but which kind?

Notes on photographs: Snow picture taken 23 February 2019; the others were taken 9 March 2019.

End notes:
1. Wikipedia. "Caragana arborescens." The tree was discussed in more detail in the post for 4 May 2008.

2. James A. Duke. "Siberian peashrub." Handbook of Energy Crops. 1983. Purdue University Department of Horticulture and Landscape Architecture website.

3. Evgeny P. Kuz’michev, Ella S. Sokolova, and Elena G. Kulikova. Common Fungal Diseases of Russian Forests. Newtownsquare, Pennsylvania: USDA Forest Service, June 2001.

4. Duke.
5. "Caragana." Agriculture and Agri-Food Canada website.
6. Agriculture Canada.
7. Wikipedia.

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.

Notes:
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.