Water stress wilts cacti

: I enjoy reading your column in the Las Vegas Review-Journal and now I have a question about my cacti. They have been wilted or thin for about 8 months. I bought them in October 2006 and planted them in the ground. Then, about March 2007, I placed them into containers; you can see them in the pictures I sent. They were wilting somewhat before I replanted them.

What is wrong with them? Do they have a fungus? Also, I forgot what kind of cactus they are.

A: The cacti appear to be a type of Opuntia, sometimes commonly called prickly pear or beaver tail cactus. These are the cacti that have flattened, circular pads and are quite common in our deserts.

From your pictures, these pads appear to be planted in a container and potting soil mix. (Those of you who subscribe to my newsletter will see pictures; you can subscribe for free by e-mailing me at Morrisr@UNCE.UNR.edu.)

Your cacti do look pretty bad. All of the pads are shriveled like flattened raisins. Cacti like this are usually suffering from water stress: not applying water often enough.

It also can be a sign of root or pad rot developing below ground. Keeping a soil too moist can rot roots and the pad below ground. That, too, is water stress since there are not enough roots for the cactus to bring water to the pads.

These problems are remedied by making sure the soil you use drains easily after irrigating and scheduling your irrigations less frequently.

If the pads and roots appear to be healthy, then the plants are, most likely, not getting watered often enough. Water plants in the ground less often than the same plants growing in containers. The smaller the container, the more often you will need to water. If those same plants were in small containers like yours, I would be watering them every couple of days.

Nopal cactus at the University of Nevada Cooperative Extension Master Gardener Orchard in North Las Vegas, which are Opuntia from the Sonoran Desert, are watered no more than once every two weeks during the hottest part of the summer. This, along with adding compost and making sure the water is draining, causes these plants to grow at tremendous rates. From a single pad planted in the ground, we can expect to produce a plant 3 feet tall in one season.

Although the pictures did not look like the cacti were damaged by freezing, that may be a possibility. Some Opuntia cacti will not tolerate temperatures much below freezing. Extreme cold or freezing may cause this kind of damage to sensitive plants.

Nopal cacti begin to show damage from freezing at 26 F, provided there is no wind. If temperatures drop below 20 F, the pads will shrivel and wilt, similar to the damage in your pictures. Our winter low at the orchard so far has been 17 F and caused severe damage to our nopal cacti.

It does not look like your plants will recover. I would try propagating them again, but avoid planting pads in the fall months. Plant them much earlier than that to give them a chance to root before winter.

Prickly pear cacti are propagated by cutting a mature pad from the mother plant with a sharp and sterile knife directly at the joint between the pads. This is done during the late spring or summer, not during the fall months. Once the pad is severed from the mother plant, the wound needs time to heal before planting it. Healing the pad is done in the shade outside for seven to 10 days.

Once healed, plant the pad in soil that drains easily and has been amended with compost and a starter fertilizer. The pad is planted upright with the bottom third of the pad below ground. The pad should be oriented when planting so that both flat surfaces receive sunlight; one side receives morning sun while the other side receives afternoon sun.

Bob Morris is an associate professor with the University of Nevada Cooperative Extension. Direct gardening questions to the master gardener hot line at 257-5555 or contact Morris by e-mail at extremehort@aol.com.