Saguaro

Carnegiea gigantea

About the Plant

Saguaros, the largest cactus in the United States, are found only in the Sonoran Desert, in Arizona, California, and Mexico. Under optimal conditions, like those found in Saguaro National Park in the Tucson area, large saguaros can make a forest.

Slow growing, saguaros in the wild can take 30 years to reach a height of 3 feet. The first flowers appear when the plant is about 8 feet tall (40-75 years), the first arms when the saguaro is between 50 and 100 years of age. Growth is faster if ample water is provided and pampered plants can reach flowering size in as little as 15 years.

The unusual crested form of a saguaro cactus

Saguaros are available as both seed grown nursery plants and dug, rescued plants. Small rescued saguaros are often transplanted successfully (care must be taken in initial digging) and two people can plant a 2-3 foot saguaro. Larger saguaros, to 8-10 feet, can also be transplanted successfully but they are heavy and planting is best done by a professional. Once planted and established, saguaro need little care. Smaller plants can be placed in the shade of a tree.

If you are planting a saguaro, make sure to select a location with well-drained soil and away from irrigation or wet areas. Make sure the original orientation of the cactus is marked (for example, a black mark with a Sharpie on the south side) and then plant in that same orientation. Do not water for the first two weeks, then occasional watering (1x per month to 1 foot depth) during the hottest, driest months for about a year will help establishment. Do not water in winter. There is usually no need to water during monsoon.

Notes:

  • Saguaros are Protected Arizona Native Plants. Digging and moving restrictions apply. If you are purchasing a rescued plant, make sure it has been harvested legally and that a native plant tag and seal accompanies the plant.
  • The flower of the saguaro is the state flower of Arizona.
  • Bacterial necrosis of saguaros is a serious disease that can spread to other saguaros. You can find out more info here, page 6. The large cactus shown below is infected and was removed.

Wildlife value: flowers provides food for bees, bats, birds. Fruit provides food for birds and other animals, including humans. Stem and arms provide nesting sites for woodpeckers and other birds (see photo below). Fallen saguaros become homes for snakes, rodents, lizards and other invertebrates. For more information, see the article in A Natural History of the Sonoran Desert cited below.

More Information

How to Transplant a Cactus from Arizona Cooperative Extension (see page 3)

Transplanting Saguaros from Central Arizona Cactus and Succulent Society

Horticultural information from ASU

Map of distribution in US (yellow means plant is rare)

Technical botanical description from SEINet

In books:

Field Guide to Cacti and Other Succulents of Arizona, Breslin, et al., page 36.

A Natural History of the Sonoran Desert by Arizona-Sonora Desert Museum, page 183. Read extract.

The Saguaro Cactus, a Natural History

 

ID Characteristics

 This plant is in the Cactaceae - the cactus family.
Saguaro cactus can grow to 40 feet in height. Young plants are often found near a nurse tree that provides shade. Saguaros grow first as a tall, single stem that eventually produces multiple branches at a height of 7-9 feet (see photos under About the Plant). The central trunk of old saguaros can be 2 feet in diameter.
The cylindrical stems are ridged, each ridge lined with clusters of hard spine along the lower 8 feet and flexible bristles above. The pleats between the ridges allow the stem to expand as the plant takes up water or to shrink as water is lost. The outer skin is a thick cuticle that prevents water evaporation. Roundish pads called areoles occur at 1-inch intervals along the ridges and produce the spines. Each aerole has about 30 spines, a few up to 2 inches long. The spines help protect the stem from some herbivores and provide shade.
The lower trunks of mature plants lose their spine and develop a dark, corky bark.
The saguaro stem is supported by an inner cylinder of 13-20 woody ribs which extend into the arms. As the stem ages, the ribs fuse together to form a latticed cylinder. This cylinder often remains after the saguaro dies (photo above).
The flowers appear in May and June near the tops of the stems and arms. They usually grow from an aerole. The flowers have white sepals and petals (called tepals) and are about 3 inches in diameter. They open at night and remain open until about midafternoon of the next day. They are not self-fertile but require-cross pollination for fruit production. Birds, beetles, moths, and bats can pollinate saguaro.
The fruit is at first green with dried tepals on the end. Eventually reaching maturity at 3 inches about a month after pollination, the fruit splits open to reveal a bright red pulp and many dark, tiny seeds. The sweet fruit is eagerly eaten by birds, who spread the seeds far and wide, just in time for monsoon.