GV Gardeners: Sun-loving saguaro Southwest symbol – Green Valley News

A large, well-hydrated saguaro can weigh more than 10 tons! This native cactus is protected in Arizona by regulations restricting the harvest or sale of wild saguaros. However, seed-grown plants are readily available from commercial nurseries.

Currently starting its annual bloom season, the saguaro became the official state flower of Arizona in 1931. Although portrayed in movies and advertisements throughout the Southwest, it grows only in Southern Arizona and western Sonora, Mexico.

First, a little anatomy the exterior of the saguaro is covered with a thick, waxy skin that waterproofs the surface and restricts loss of water. Just beneath this layer is a thin layer of chlorophyll-containing cells.

Outer pleats enable the stem to expand without bursting during water uptake. Clusters of hard spines along the pleats provide shade for the surface, reducing heat load and water loss. The deeper interior consists of water storage tissue.

Water makes up 75 to 85 percent of the weight of a saguaro. The retained water helps prevent temperature extremes which are harmful to the plant. A skeleton of 12 to 20 woody ribs is in the center of the stem, running through the main stem and branching into the arms. Surprisingly, roots for this giant are rarely more than 4 inches deep, radiating horizontally from the plant as far as it is tall.

White flowers open late at night and remain open until the next mid-day, releasing an aroma much like an over-ripe melon. Pollination takes place both at night when bats feed on the nectar, and during the day when bees and white-winged doves feast.

During June, the pollinated flowers mature into 3-inch fruit containing many tiny seeds embedded in the juicy, red pulp. When the rind splits and displays the bright inner lining, the open fruit is often mistaken for red flowers.

Saguaro fruit ripens during pre-monsoon drought and is often the only moist food available for wildlife. It becomes a staple for many insects, birds and mammals. Conveniently, seed dispersal takes place just prior to the summer rainy season.

From a seed the size of a pinhead, successful sprouting takes place under the protection of another plant, referred to as the nurse plant. In 10 years the plant grows to 1.5 inches high. If it survives for 30 years, the saguaro reaches 2 feet high. By 50 years, most plants flower, produce arms, and may top out at 8 to 10 feet high.

Some saguaros may have as many as 50 arms; many will never grow any arms. Studies have shown that arm production is random. Saguaro arms grow upward. Drooping or twisted arms are caused by wilting after freeze damage.

Whether with or without arms, the saguaro is a well-engineered, statuesque, sun-loving symbol of the Southwest desert and the state of Arizona.

Mary Kidnocker is a University of Arizona Master Gardener who lives in Green Valley. Her articles are featured weekly.

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GV Gardeners: Sun-loving saguaro Southwest symbol - Green Valley News