Technically defined as Madrean Evergreen Woodland intergrading with Semidesert Grassland, most of the valley consists of rolling hills of native and introduced grass species, but towards the foothills where I lived were scattered oak and juniper trees, under-storied by native Arctostaphylos, Mimosa, Rhus, Yucca, Agave, Nolina, and a few species of rock ferns and geophytes. The annual rainfall averaged 18 inches (45 cm) a year but varied between 9 and 22 inches (20-56 cm) during my dozen years at the garden. These rains (so-called monsoons), generally fell between July and September, creating an odd combination of growing conditions: wet summers and dry autumns, winters, and springs. Because even summer rainfalls were erratic, native plants could be rare one year and common the next.
My first few years were devoted to laying out the hardscape, which consisted of gravel and flagstone pathways, flagstone terraces, and some difficult digging. I incorporated about 40 tons of quarried stone into the garden (25 by hand and 15 into the boulder garden by front-end loader), 15 tons of gravel, five tons of flagstone, and 15 tons of decomposed granite. I could only work about three or four hours a day before collapsing into a pile of pain. Then I lay on the floor and cursed the day I was born.
Although this might eventually have amounted to a garden of interest, after 12 years it was destroyed in a day and night of grass fires that burned much of the garden along with fences, sheds, garden equipment, wellheads, and pumps, not to mention a few dozen aged trees in the natural areas of my property. The house survived, but after the fire water became scarce and advancing age suggested I move to more equitable climes. I now live in Eugene, Oregon.
Domesticated Rock Garden Plants
Most of the plants included in my rock garden were what one would call easy, generally commercially available, and seemingly not suitable for xeric conditions. For example, I grew Dianthus ‘Tiny Rubies,’ which was among the first plants installed in my Maryland gravel bed in 1980. The same plant was still growing when I left for Arizona in 2006. In fond remembrance, I grew ‘Tiny Rubies’ in Arizona, where it lasted (a bit less willingly) 12 years in full sun. I now grow it in my Oregon garden, where it needs restraint. I am fond of Dianthus and also grew D. microlepis with minor success in Arizona. Dianthus plumarius grew willfully, seeding itself anywhere it found a crack in the flagstone pavement or among rocks lining the gravel pathway. Whether in sand or clay, I was amazed by its absolute fondness for heat and drought. I tried several species of Campanula, with but little success, as might be expected due to xeric conditions. Campanula portenschlagiana ‘Blue Waterfall’ grew in the shade, if somewhat reluctantly. I introduced Phlox kelseyi, a xeric western native, which made a successful attempt at growing, but both it and the campanula never had a chance to spread due to the fire.
Successful growers, which might be expected based on their tolerance for dryness, included California eriogonums Eriogonum grande var. rubescens and E. fasciculatum var. foliolosum. Another heat-tolerant rock lover was Euphorbia clavarioides var. truncata from South Africa. It did well until the temperature dropped down to a mind-numbing 4°F (-15.6°C); normally we only had a few frosty days a year and rarely a few inches of snow, which melted the next day. The succulent Ruschia pulvinaris, also from southern Africa, did very well and bloomed profusely every spring despite the weather. Resembling a Delosperma, the foliage is a bit confrontational by comparison.
A great mat-forming plant, Teucrium aroanium, spread easily with little water. The lilac flowers attracted variegated fritillary butterflies by the dozens (native grassland violets are one of the common larval host plants of this butterfly). This plant has grown readily in Oregon, but it is not as compact or tidy as it was when water-stressed. Not very colorful but an equally easy mat former was Paronychia kapela subsp. serpyllifolia which grows as a green film with tiny white flowers and bracts like tissue paper. Similar in growth habit but much more attractive was Veronica liwanensis, which enjoyed the dry conditions enough to spread into the gravel pathways. Even more colorful was Genista lydia, another reminder of my Maryland garden. As might be expected, several penstemons grew well, including the native Penstemon dasyphyllus and introduced P. barbatus in both its tall forms and dwarf ‘Navigator’ series. I grew several of the larger penstemons but most were too tall for the rock area. The same was true of Salvia, though I did fit S. pachyphylla into the rockery.
Native Plants: Introduced or Naturally Growing on the Property
I grew many shrubby native plants, but few were suitable for the rock garden. Hardy zinnias, largely unknown to the rock garden community, constitute one group that attracted me. There are about a dozen hardy species native to the Southwest and Mexico. I established a large patch of Zinnia acerosa by collecting native seed and simply sowing it amongst my large boulder field. This species is widespread in barren ground and disturbed areas, performing as well in a sandy wash as on a clay hillside. It appears as a tiny, woody shrub (10 inches/25 cm tall), covered in white flowers and with needle-like leaves. As with the teucrium mentioned above, it was very attractive to variegated fritillary butterflies. The plants did not survive the fire but reappeared sparsely the next year. Another species, Zinnia grandiflora, bearing yellow flowers with an orange center, much prefers grassland clay soil. A ground cover, the single plant that survived the fire, spread by underground rhizomes to fill a square yard (0.8 square meters) of my boulder garden. Zinnia citrea, raised from seed and similar in size to Z. acerosa, had solid yellow flowers but did not grow readily or survive the fire. These zinnias are difficult to find in the trade, either seeds or plants, and I suspect they would do poorly in non-xeric sorts of gardens.
Appearing nearly identical to Zinnia acerosa, Melampodium leucanthum (blackfoot daisy) was much easier to grow and easier to obtain seed. I introduced seed to the boulder garden and the plants grew well, even surviving the fire.
A native plant of great beauty, Lithospermum incisum, turned up on its own as a permanent visitor to the boulder garden. Well worth having, but elusive in my area, I made no attempt to propagate it. At some point, a plant called sand bells (Nama hispidum) seeded itself in two different flagstone walkways. I had no idea where it came from, but it was about as pretty as a “weed” could get. An annual mat-former with purple flowers, it bloomed over a long stretch of time and reseeded every year.
A yellow form of Calochortus kennedyi grew near my driveway in solid clay soil. Oddly, it seemed as if planted in a row. Within 1000 feet of my property a patch of mixed calochortus bloomed, including an orange form of C. kennedyi and white and pink forms of what I believe to be C. ambiguus. I was never quite certain of their identity. I didn’t have the heart (or strength) to attempt transplanting any of these to the rock garden; it would have taken a pickaxe. They were an inspiration where they bloomed!
A few additional rock garden worthy plants that grew on my property included the common and widespread Glandularia (syn. Verbena) gooddingii. It did perfectly well on its own, especially after the fire when bare ground was exposed. The purple flowers smothered the foliage, forming manicured mounds. The uncommon spider milkweed (Asclepias asperula) was interesting in structure and flower, and low enough to fit into any rock garden, but I imagine it would only appeal to an entomologist such as myself.
Attempting to garden in a xeric garden, with poor soil, was a challenge, perhaps not suitable for an “elderly gentleman,” as I am sometimes referred to. The weather, at 5000 feet, was entirely enjoyable, as was the constant light, the thunderous summer rainfalls, and the minor successes that could be achieved. Unfortunately, 12 years is not long enough to claim any sort of victory—there seldom is in a garden—but it was fulfilling while it lasted.