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The Healthy Saguaro

Author: Cathy Babcock
Issue: July, 2017, Page 104
How to know when your desert giant is ailing

Nothing says “Arizona” more than the saguaro cactus (Carnegiea gigantea). Who wouldn’t want this majestic, iconic plant as part of their landscape? However, its awesome size can sometimes cause equally imposing issues. 

One common question that homeowners frequently have is if the holes in a saguaro are a reason for concern. The answer is typically no. Most holes are caused by Gila woodpeckers and gilded flickers. They make their nests in the trunks of saguaros by hollowing out a space in which they will raise their young. In response to the birds’ activity, the wound created will dry out and harden off, forming a callus. Because the shape of the nest often resembles a shoe, these cavities are known as saguaro “boots.” The birds keep the nests cleaned out and, when abandoned, other birds, such as elf owls and house finches, often move in, with the saguaro serving as a hotel of sorts. There is no practical method for deterring the woodpeckers. While the nesting holes pose no serious threat to the plant, many fastidious homeowners want their cactus to look perfect, without blemishes.

A more serious problem is when a saguaro begins to show symptoms of bacterial necrosis, or rot, caused by Erwinia cacticida. The bacterium enters the plant through injuries caused by insects, small animals, or mechanical or frost damage, and can be identified by a black ooze that seeps out of the saguaro’s trunk. If the injury is localized, the infected area can be cut out with a sharp sterilized knife. Be sure to resterilize the knife after each cut, and then treat the area with a 10 percent bleach solution and sulfur, allowing it to dry out afterwards. Do not try to seal up the wound with concrete or any other homemade concoction. Once tissue is cut from a plant, the area will not grow back. Instead it will harden and form a callus similar to the bird nest cavity. It is essential that all discolored and dead or rotten tissue be removed back to healthy tissue. Be sure to angle the cutout area so that water will drain out instead of pooling within the pocket. Discard all plant tissue in a sealed plastic bag and rinse the area around the base of the plants. If the diseased area is large, call a professional cactus expert who can advise you on whether the cactus is too far gone to save. Because bacterial necrosis can be spread to neighboring saguaros through insect activity, immediate removal of the infected area is important.

Frost damage on a saguaro growing in the Valley is rare and more likely to occur at a higher elevation or in an area that is more prone to prolonged periods of freezing temperatures. Frost damage can take a long time to manifest. Often an arm of the cactus will break off or swing downward as a result. If this happens, just let the wound dry out naturally. 

And then there are the leaners. There are a number of reasons that a saguaro might lean: too much shade from the house or a neighboring tree, overwatering resulting in bacterial necrosis at the base, too many heavy arms on one side causing unbalance, soil that is too wet and loose, or too much soil at the base. A slight lean is probably nothing to worry about. If the lean is so severe that you are worried that the cactus may fall over—especially when other valuable plants or structures might be impacted if it topples—call a professional who specializes in sick cacti. Both Desert Botanical Garden and Boyce Thompson Arboretum have a list of companies that provide saguaro services, including general care, relocation, salvage and removal.

When transplanting a large, mature saguaro, try to ascertain whether the plant was grown in the shade or in full sun before you received it. If grown in shade, it will need shade cloth for the first year. Always mark the orientation and plant accordingly to avoid sunburn. A sunburned cactus will show brown discoloration, and once the tissue becomes necrotic the damage cannot be reversed.

Avoid planting near any drip emitters or lawn sprinklers, or you will risk ending up with a rotten plant from too much water. If it is a young plant, consider placing under a “nurse plant,” such as a mesquite tree, which will protect while it is small. When planting your baby saguaro, keep in mind that that cute little thing will grow up to be the giant majestic plants seen in the desert. Always remember: right plant, right place. Once a saguaro begins developing arms, it is more difficult to transplant successfully.

With a projected lifespan of up to 200 years, mighty saguaros are built to last. Keeping an eye out for signs of stress can help ensure that yours have a healthy life.

Cathy Babcock is the director of horticulture for Boyce Thompson Arboretum, located in Superior.
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