BY SCOTT OGDEN / Austin, Texas, USDA Zone 8
TO DO IN THE GARDEN
In central Texas, spring is leaf-collecting time. Live oaks are making messes all over as they annually shed leaves, tassels, and copious golden pollen. Potential compost is everywhere. To improve garden soils in a casual way, simply scatter native oak leaves as mulch 3 to 12 inches deep over beds and borders, taking care not to smother delicate plants; most will rot down to humus by the end of the summer.
Each time I sink my shovel into the dark clay in my backyard, a part of me feels like I’ve slipped back in time. Technically, the chalk age ended 65 million years ago when a giant meteor landed near Chicxulub in the Yucatan. The dinosaurs perished in the catastrophe, along with the ammonites, marine creatures whose baroquely coiled fossils peer from the limy rocks of Texas and other chalky places, like the white cliffs of Dover, which were once covered by the Cretaceous seas. That exotic world vanished long ago, but the gardens I cultivate make me a participant in prehistory. The earths with which I contend derive directly from a lost ocean.
Calcium montmorillonite. The mellifluous name of the mineral component of the Texas blacklands belies its challenging properties: a crystal lattice with a two-to-one expansion coefficient, terrifying to civil engineers and to agencies that insure slab foundations; an often uncorrectable pH of 8 or more; and, in Texas’s subtropical climate, the tendency to form “vertisols”—soils that annually dry and crack, forming deep crevasses that swallow surface debris, so that they continually churn over themselves. These “gumbo” soils thwarted settlers with boggy swales, known in the curious Russian dialect of soil science as “gilgai structures” and in the parlance of the pioneers as “hog-wallows.”
Tall grasses formerly grew here and fed the intractable earth with a steady diet of rough debris, but after a century of fertility-robbing crops like cotton and corn—or, on thin, rocky ground, cattle, sheep, and goats—most Texas soils now come to gardeners exhausted. The calcareous mineralogy and the torrid climate dissipate humus at alarming rates. Although organic mulches added several times each year eventually restore fertility, it’s a challenge to cover a large property, and few gardeners relish the aesthetic impact of perpetual “sheet composting.”
There are plants that sympathize with this dilemma. The native redbud, Cercis canadensis var. texensis, like other legumes, thrives on depleted soils, fixing the nitrogen it needs directly from the air with the help of bacterial nodules along its roots. Where clays are mucky, bulbous plants like oxblood lily (Rhodophiala bifida) and Byzantine gladiolus (Gladiolus byzantinus ‘Cruentus’) make brilliant use of surfeit winter moisture, leafing out and blooming during the cool parts of the year, then becoming dormant, pulling downward with contractile roots as the adobelike substrate dries in summer. In reality, a long list of odd plants seems entirely content in these soils.
During first-grade recess, I used to endure skirmishes with classmates throwing bunches of sharp, pointy seeds gathered from the native speargrass, Nassella leucotricha. I sought refuge from my attackers behind an old bois d’arc tree, where I quietly sat and sifted the cracked, black earth for pearly calcite prisms left by ancient fossil oysters. Nowadays I turn up the same shelly fragments while digging with my border fork. When I do, I am reminded that my garden grows on a foundation of life. The chalky rocks themselves, the dark, sticky clays that weather from them, the curiously tolerant plants—all represent riches passed down from a living past. Like any garden, mine grows as an inheritance of those who have gone before, gardeners and ammonites included. H
Little bluestem (Schizachyrium scoparium)
Once a principal component of tall- and midgrass prairies across North America, this attractive grass presided as one of the original soil-builders. It makes a superlative garden plant, with two- to three-foot clumps of erect, linear foliage, often dusted with silvery blue powder. Feathery bloom spikes appear in late summer, reaching four to five feet, and the whole plant turns russet bronze in cold weather, maintaining a glowing translucence in winter light. For little bluestem, an annual late-winter shearing is the only effort required of gardeners; in return, these grasses will steadily restore the soil. Be patient. USDA Zones 3–10. Sources, page 122.