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  Tucson Cactus and Succulent Society

Growing Succulents in the Desert Column

(List of Growing Succulents in the Desert columns)

"Coping with Wet Winters" by Mark Dimmitt

(This article may only be reprinted with the author's permission.)




In early 2011 Southern Arizona gardens suffered from a hard freeze, the worst since 1978. Now we have to deal with another potential problem that we haven’t seen for a couple of decades - a very wet winter. Weather statistics fail to capture the issue. 2011 will go down as a barely above average rainfall year. Even if you look at the totals for November and December, neither of these months was anywhere near setting a record. The problem was in the frequency of storms. It rained at least once a week for seven weeks. Biologically that is very wet, because the soil has been continuously moist for all that time.

Roots, like all plant tissues, require oxygen for respiration. When soil is saturated, all the air is displaced by water, so respiration becomes impossible. There is usually no problem for plants in the ground. Rainwater percolates downward, and in non-clay soils the root zone does not remain saturated for more than a couple of days. Potted plants, though, are in danger; water cannot percolate beyond the bottom of the pot. After a heavy rain or irrigation, the bottom few inches of the potting medium remain saturated until the water evaporates or the roots absorb it and the plant transpires it. But many of the cacti and other succulents we grow are winter-dormant; they have minimal metabolic activity during the cooler months. In addition, there isn’t much evaporation when the weather is cool. After several days without air, roots suffocate, die, and then rot.

The best solution to drowned roots is prevention. Plants can be kept under a rain shelter while they’re dormant. If grown in the open, make sure that the potting medium is very well drained. In my opinion, most collectors whom I’ve visited use dangerously tight potting media. Most commercial growers also use very tight media. They have valid reasons: 1. Many of their plants are under cover where rain is not a problem. 2. They can’t afford the additional time and cost of irrigating hundreds of thousands of plants in coarse media. That’s the only negative - the coarser the medium, the more frequently plants must be watered during the growing season. Collectors,however, should be more concerned with the long-term survival of their cherished specimens than how often they have to water. Remember: succulents are better adapted to drought than to soggy roots.

An important side note: Placing a layer of coarse material such as rocks or plastic peanuts in the bottom few inches of a pot does NOT improve drainage; it makes it worse! This is a law of physics that cannot be broken. Water cannot move from a finer textured medium into a coarser medium until the bottom of the upper layer is saturated. So a layer of coarse material beneath
a regular potting mix simply moves the saturated layer higher in the pot, closer to the base of the plant and thus increasing the danger of rot.

If you have a succulent that is rotting at the base, unpot it immediately, wash off the medium, and cut off dead tissue. Consider treating the cuts with a fungicide such as dusting sulfur. Store the plant upright in a dry place until its growing season begins. Then repot and hope for the best. And before you repot, consider changing your medium.

If you have a succulent that is rotting at the base, unpot it immediately, wash off the medium, and cut off dead tissue. Consider treating the cuts with a fungicide such as dusting sulfur. Store the plant upright in a dry place until its growing season begins. Then repot and hope for the best. And before you repot, consider changing your medium.

A final note: Winter-growing plants like most Crassulaceae and aloes are prone to rot if they’re too wet during their summer dormant season.