Cacti of the Sonoran Desert

After a few days in the Sonoran Desert, my head is filled with thoughts of cacti.

I attended the annual meeting of the Garden Writers Association, attended by writers from many parts of the United States. This year’s meeting convened in Tuscon, Arizona, which is within the upper part of the Sonoran Desert’s 120,000 square mile area, most which is in Mexico.

We locate Tuscon in our southwest; Mexicans see it in their northwest.

The meeting included talks to inspire writing or teach up-to-date written and multimedia communication, numerous awards for outstanding writing, photography, videography and graphics, many exhibits by garden-related vendors, and bus trips to twelve public and private gardens in the Tuscon area. Visit ongardening.com for more of my travel notes and photos.

For me, the primary effect of this occasion was exposure to the distinctive plant life of the area, especially the Cactus family, almost all members of which are native to the Americas.

The most prominent local cactus is the stately Saguaro (Carnegiea gigantea), which grows in the wild only in the Sonoran Desert. I saw specimens of about thirty feet high, but it can reach up to fifty or seventy feet.

Other cacti widespread in the area include the Cholla (Cylindropuntia spp.), Beavertail (Opuntia basilaris), Hedgehog (Echinocereus spp.), Fishhook (Ferocactus wislizeni), Prickly Pear (Opuntia spp.), Night-blooming Cereus (Peniocereus spp.), and Organ Pipe (Stenocereus thurberi).

According to Sunset’s Western Garden Book, these cacti could be grown in the Monterey Bay area, but we see them infrequently. This presumably reflects local gardeners’ preferences: with such a wide range of plants that thrive in our moderate climate, gardeners have many spineless horticultural options.

There are, however, important environmental conditions other than temperature that affect the growth of plants. Plants that grow in the harsh conditions of the Sonoran Desert have evolved to adapt to the desert climate, characterized by a biseasonal rainfall pattern (late summer and early winter), and daily temperature ranges of about thirty degrees.

The Sonoran Desert also includes plants from the Agave, Palm, and Legume and other families. The large Legume family includes many varieties of peas and beans, plus alfalfa, clover, lentils, lupins, mesquite, carob, soy peanuts, Locust trees, wisteria and the green-trunked Palo Verde (Parkinsonia aculeate), which grows throughout the Tuscon area.

I have had no cacti in my garden, but the friends who hosted my visit gave me two specimens: a hybrid Echinopsis ‘Los Angeles’, which will grow to about eighteen inches, and produce pink flowers in late spring and early summer, and a Echinocereus morricalii, which also will grow to about eighteen inches and blossom in May in bright magenta.

Many cacti would not fit easily in my garden, but these small plants will fit fine and provide gorgeous flowers. Travel could broaden our gardening tastes!

More to come

Gardener’s Gold

If you have deciduous trees in your garden, you might be fretting these days over the task of raking and disposing of the fallen leaves. You might instead welcome this form of nature’s bounty, because your trees have contributed the raw material for an excellent natural resource for your garden: leaf mold.

Leaf mold, which is simply partially decomposed leaves, can be used as a mulch to discourage weeds, retain moisture and insulate the roots of plants from the coldest weather. It can also be used as a pH-neutral soil amendment, like compost, to retain moisture, improve soil texture, add nutrients and support the growth of beneficial soil organisms of all kinds.

The question, then, is how to convert the fallen leaves to leaf mold.

The raking can’t be avoided, but the rest of the task could take any of several forms, depending on the gardener’s patience and available space, and the kind of leaves. Some leaves, including oak and holly, contain relatively high levels of cellulose and are slower to break down.

The easiest conversion of leaves to leaf mold is to pile the leaves in an out-of-the-way location and let them decompose on their own schedule. This process could require a year or more, but could be hastened in several ways, singly or in combinations.

  • Leave your leaf pile in a shaded location, or cover it with a plastic tarp. This helps to retain moisture, which supports the decomposition process, which depends upon the work of fungi.
  • Water the leaf pile occasionally, to maintain a damp (not soggy) condition.
  • Turn the pile occasionally, to expose the contents to oxygen.
  • Shred the leaves. Smaller pieces have greater exposure to the air and moisture, and therefore break down faster. Run over the leaves with a lawn mower—almost any kind would do—or put them through an electric leaf shredder or leaf blower-vacuum. My American Sycamore’s big leave tend to block my blower-vacuum, so they have to be roughly shredded first with the mower. For smaller quantities, place the leaves in a trashcan and shred them with a weed whacker.
  • Add nitrogen. Old dry leaves are almost all carbon, so the addition of nitrogen will speed their breakdown. Add green vegetation or nitrogen-rich fertilizer. Dry chicken manure has twice the nitrogen content as horse or steer manure.

The leaf mold is ready when it has become soft and crumbly. Use it to mulch your plant, spreading it about three inches deep (not too close to the base of the plant). Or dig a similar amount into the soil; this could be easiest when preparing a new bed, and is particularly helpful for improving soil that contains an excess of clay or sand. Leaf mold also could be included in containers to lighten their weight.

Enjoy gardener’s gold in your garden!

Growing Terrestrial Orchids

Most orchids are epiphytes, meaning that they grow on another plant. Epiphytes are not parasites, which are plants that scrounge nutrients from another plant. An epiphyte attaches itself to another plant (a tree, usually) and gets moisture and nutrients from the air and rain and sometimes from debris accumulating around it.

To grow an epiphytic orchid, the gardener must reproduce the temperature, humidity and light level that the plant has evolved to require. This is true for all plants, to be sure, but these orchids have become accustomed to very particular environment that can be difficult for the gardener to provide.

Experienced orchid growers claim that success with epiphytic orchids requires only creating the plant’s preferred conditions. This typically includes planting the plant in coarse bark chips to provide ample access to air.

Without denying the accomplishments of amateur orchid growers, I confess to having killed more than my share of epiphytic orchids.

Given that sad history, I am delighted to have discovered hardy terrestrial orchids. These are plants that thrive in well-drained soil and within a moderate climate like that of the Monterey Bay area. Some terrestrial orchids will even take freezing temperatures.

Terrestrial orchids that are popular for home gardens have been described in three groups according to water needs:

  • Upland species include Lady’s Slipper (Cypripedium), Chinese Ground Orchid or Hyacinth Orchid (Bletilla) and Hardy Calanthe (Calanthe);
  • Transitional species include Grass Pink (Calopogon), Marsh or Spotted Orchid (Dactylorhiza), Egret Flower (Habenaria), Fringed Orchid (Platanthera), Fragrant Ladies’ Tresses (Spiranthes), and Helleborine (Epipactis);
  • Wetland species include Rose Pogonia (Pogonia).

Three years ago, I acquired a small Lavender Chinese Orchid (Bletilla striata), which is widely available, and planted it in semi-shade, assuming that all orchids want shade. Although I never watered or fertilized the plant, it grew well but produced only occasional blossoms. This was disappointing because Bletillas often will have as many as 20 flowers on a single spike.

Then I learned that this plant prefers full sun exposure. I lifted it and discovered it had developed about twenty pseudobulbs, which are storage organs (like tubers) that some orchids produce. These can be planted six inches apart, about three inches deep, so I should have several patches of these plants in bloom in the spring.

Terrestrial orchids can provide an exotic display in the garden without requiring extraordinary care. The Chinese Ground Orchid is particularly easy to grow, and the Lady’s Slipper and Hardy Calanthe are also good choices for most gardens. The Transitional and Wetland species require more moisture, making them inconsistent with water conservation goals, but a small display would be tolerable.

If you enjoy the unique beauty of orchids, but have had poor experiences with epiphytic species, growing terrestrial orchids could be an appealing option.

More

Here are current books about the  cultivation of hardy orchids.My principal reference for this column was the Mathis book, but other books listed offer additional information and other perspectives.

  • The Orchid Manual: For the Cultivation of Stove, Greenhouse, and Hardy Orchids, With a Calendar of Monthly Operations, and Classified Lists of Species, by Thomas Appleby. Forgotten Books (June 23, 2012) (Note: this is a reprint of a classic book published in 1845.
  • Growing Hardy Orchids, by Philip Seaton, Phillip Cribb, Margaret Ramsay and John Haggar. Royal Botanic Gardens, Kew; Original edition (March 15, 2012)
  • Growing Hardy Orchids, by John Tullock. Timber Press (September 15, 2005)
  • The Gardener’s Guide to Growing Hardy Perennial Orchids, by William D. Mathis. The Wild Orchid Company (2005)
  • Hardy Orchids, by Phillip Cribb and Christopher Bailes. American Orchid Society (December 1989)
  • Hardy Terrestrial Orchids for Perennial Gardens with a focus on Bletilla, Calanthe, and Spiranthes – Excluding Cypripedium, by Dennis Carey & Tony Avent. Plant Delights Nursery Inc.

Selected sources of hardy terrestrial orchids:

 

 

 

 

 

Small Gardening

The gardening world has been buzzing about small gardens. The current interest in this topic might reflect a trend toward small-scale properties or growing desire among gardeners to limit the time and energy they commit to gardening.

A small garden could be the entirety of a small property or an area within a large property. A large property might include several small gardens (sometimes called “rooms”) or one small garden plus undeveloped space, or something between those extremes.

In either case, the goal for small gardening should be quality gardening.

“We would do well to follow a common rule for our daily lives—do less, and do it better.” (Dale E. Turner)

When developing a small garden, all the usual criteria for plant selection and cultivation are applicable. Ensure that the soil is fertile, friable and well drained, and choose plants that are appropriate for the climate, sun exposure and prevailing winds of the garden.

In addition, three broad guidelines come to mind.

First, specify a theme beyond “small size.” The garden might focus on a genus (rose, iris, clematis, etc.), a category of plants (succulents, white blossoms, herbs), a plant community (California natives, African bulbs, aquatic plants) or any other theme of interest. A theme provides coherence to the garden and a rational approach to plant selection.

Second, provide a story line for visitors. The garden planner could guide a visitor’s attention by establishing a focal point: a well-placed, exceptional plant, a piece of garden art, or a water feature, etc. After that initial impression, the gardener or discrete signs might encourage a visitor to examine a series of specimen plants. A rose garden, for example, might showcase several hybrid teas or species roses for comparison.

Finally, plan the maintenance of the small garden for close inspection. No garden looks good when unkempt, but a neglected small garden can be particularly unsatisfying to both the gardener and the visitor. While fallen leaves, a forgotten watering hose and a few weeds can be tolerated in a large, sprawling garden, a small garden should be raked and pruned and tidied regularly. By virtue of being small, it should also be manageable.

The small garden is to a large garden as a sonnet is to free verse.

More

Here is a link to an article with additional thoughts about small gardening: “Big Help for Small Gardens.”