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Growing Succulents in the Desert Column, May 2010

(List of Growing Succulents in the Desert columns)

Trichocereus hybrids explode in May (and beyond)

By Mark Dimmitt and Mark Sitter

(This article may only be reprinted with the permissions of the authors)

Trichocereus hybrids, sometimes called torch cacti, put on magnificent displays of large, brilliant flowers. Collectors will throw impromptu parties when all their plants bloom on the same day. Locally, blooms may start as early as mid March. However, the first big flush of blooms is usually in early May, followed by more through mid summer. The best cultivars will bloom massively every 10 days to two weeks over a span of three months. There are often occasional flowers in between the big shows, and sometimes continue into autumn. Each flush lasts one to three days. If you want to snarl traffic or cause streams of onlookers or photographers to congregate, these are the cacti you want to plant in your front yard or other public place.

First, a Taxonomic Note: Botanists have lumped most of the members of this large group of South American cacti in to the single huge genus Echinopsis. The former genera included Echinopsis (sensu stricto), Lobivia, Trichocereus, Helianthocereus, Soehrensia, and a few more. Many horticulturists, including the authors, do not accept this. The great majority of species easily fit into one of the former genera, and each has distinctly different growth forms, flowers, and cultural needs (Figure 2). A brief summary of the most commonly grown ones:

Echinopsis (sensu stricto): Smallish globular plants (mostly 6-12 inch tall stems) with large, white or pale pastel, nocturnal, moth-pollinated flowers with very long floral tubes. The dried fruit can be easily crumbled to release the seeds.
Lobivia: Small globular plants with small, brightly colored, diurnal, bee-pollinated flowers with shorter tubes than those of Echinopsis. Same fruits as Echinopsis.
Trichocereus: Some restrict this genus to the columnar shrubs to trees with very large, white, nocturnal, moth- or bat-pollinated flowers with long tubes. Examples include T. terscheckii, pachanoi, and spachianus. The seeds are embedded in a sticky mucilage. Whether harvested wet or dry, the pulp must be macerated in a large volume of water to extract the seeds. Some taxonomists include the next
genus in Trichocereus:
Helianthocereus: Medium-sized plants resembling oversized North American hedgehog cacti (Echinocereus) that bear large, brightly colored, diurnal, bee-pollinated flowers with short tubes (a few have white, nocturnal flowers). Fruit same as in Trichocereus.
Soehrensia: A small genus of about 10 species of mostly single-stemmed plants resembling North American barrel cacti (Ferocactus). They bear smallish, brightly colored, diurnal, bee-pollinated flowers with almost no tubes.

Echinopsis and Lobivia are mostly high elevation Andean species. They require special care to grow them well in the extreme heat of the low desert. On the other hand, Trichocereus and Helianthocereus are very tolerant of both hard frosts and desert heat. They are superbly adapted to growing in our climate. (When we use trichocereus without the italics, we are referring mostly to Helianthocereus, Soehrensia, and their hybrids, including with Echinopsis and Lobivia. Except for T. spachianus, the arborescent Trichocereus species will not hybridize with others in this group.)

Development of South American cactus hybrids
The numerous species in the Echinopsis-Trichocereus complex cover a great range of flower colors and sizes, and many of the species hybridize readily. Echinopsis – Lobivia hybridization got serious in the 1950s and 1960s with Johnson Cactus Gardens’' Paramount Hybrids. Development continues today with the Schick Hybrids being offered through Huntington Botanical Gardens’'International Succulent Introductions. These plants are a bit small for landscape use, and, as stated earlier, are a little delicate in hot desert climates. Trichocereus – Helianthocereus – Soehrensia hybrids are larger plants with big flowers that are suitable for planting in the ground. They are also well adapted to desert Southwest’s low elevation climates. Hybridizing them with Echinopsis and Lobivia preserves their size and desertadaptedness, and adds even more flower forms and colors to the palette. Bob & Bev White, the founders of B & B Cactus Farm in Tucson, and Mark Dimmitt created a number of hybrids in the 1980s and 1990s, using species and a few early hybrids of unknown origin. (The Whites did not keep records, so it’s difficult to determine which cultivars are their creations.) There is another center of Trichocereus hybridizing in Germany. But because of CITES, there has been very little international trade

Trichocereus hybrids grow well in large pots or in the ground in the desert Southwest. Some growers can adapt them to full sun, but to avoid sunburn it’s safer to grow them in light shade, as under an unirrigated mesquite or palo verde tree. They respond dramatically to generous water and fertilizer. With weekly watering and monthly feeding, the best cultivars will flush massive blooms every two weeks or so for three months or even longer. With water restriction, bloom will be much reduced in number. (Some clones will flower for only one or two days a year; there is a great deal of genetic as well as cultural variability.) The authors obtain superb results using a water soluble ‘Bloom’ formula fertilizer, one with low nitrogen and high phosphate. Deadheading (cutting off the spent blooms) close to the stem will result in greater flowering potential since the plants may often abort new flower buds in favor of producing fruit from pollinated flowers. Trichocereus flowers may be enjoyed as cut flowers indoors in water.

If you live in the desert, you’ll need to protect your trichos from javelinas, rabbits, squirrels, or even deer; they will eat your flowers. Additionally, insect pests may include, the giant cactus beetle, Moneilema gigas, the cactus weevil, Cactophagus species, thrips, and cactus moth (blue cactus borer), Cactobrosis fernaldialis. These can easily be treated with regular applications of systemic insecticides.

List of Growing Succulents in the Desert columns