Getting its name from the Greek lithos meaning stone, and ops meaning face, this is a fascinating genus displaying an infinite variety of color and markings and an extremely simplified plant structure.
The first thing to remember about Lithops is that they are native to areas of Southern Africa that are extremely dry, in some areas having to survive prolonged drought which may last for well over a year.
The primary requirement with regard to soil is good drainage. A cactus mix with additional coarse sand or pumice works fine. It should feel quite gritty and should fall apart readily when wet. Use either clay or plastic pots according to preference, but make sure that any pot used has a drainage hole.
Lithops and other mesembryanthemums (“mesembs”) are true “sun worshipers.” Give them as much light as possible, remembering that any plant needs protection when exposed to bright light after being in a shady location. They can handle minimum temperatures of 40° F and even lower.
With regard to watering, the best advice is still “When in doubt, don’t!” It’s important to understand the growing cycle of Lithops to understand when they can make use of water and not to just water because it seems like it’s been a long time.
Just because the old leaves are beginning to shrivel in winter after flowering doesn’t mean the plant is dormant. The new leaves are growing inside the old ones at this time. Because the plant is getting moisture from the old leaves, it doesn’t need to be watered. However, after the old leaves are mostly consumed, additional water can be provided into the spring and possibly summer.
During the heat of summer after the new leaves have developed, the plant may go dormant and won’t need to be watered. If the plant begins to shrivel, some growers mist the plants in the evening once in a while.
The most important time for watering is in the late Summer and early Fall as the flowering period approaches, slacking off as winter approaches and moisture is absorbed from the old leaves. At all times, they benefit from good air circulation.
In summary, the primary times for water are in the Spring and Fall, with no water during the winter and less water during the heat of summer.
Luckily, Lithops are not susceptible to a large number of plant pests. Slugs and grasshoppers can be a problem when plants are in a greenhouse or outside, and, from personal experience, squirrels, chipmunks and the occasional mouse find them to be delicious, especially the more expensive and rare ones! Mealybugs may hide between the old dried leaves and the new ones and red spider may occasionally cause a problem. Treatment is seldom a major problem.
A final note: Over watering and excess humidity are the number one causes of problems with Lithops. Again, when in doubt, don’t!
(This document is also available in PDF form here. You will need an Adobe Reader to read this file, available free here.Copyright©2012 Kara Nursery
Lynn-Marie Kara & Luther Sturtevant