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Lithops (commonly called
„flowering stones“ or „living stones“) are true mimicry plants: their shape,
size and color causes them to resemble small stones in their natural surroundings.
The plants blend in among the stones as a means of protection. Grazing animals which
would otherwise eat them during periods of drought to obtain moisture usually
overlook them. Even experts in the field sometimes have difficulty locating plants
for study because of this unusual deceptive camouflage.
In the wild, Lithops inhabit vast dry regions of southern Africa. Several areas in which these plants grow receive less than 2 inches of rainfall per month throughout the entire year. In an extreme situation of low rainfall, at least one species of Lithops depends on mist or fog to provide its main source of moisture *. Lithops could not survive in many areas that they are found were it not for their capacity to store water. In fact, almost the entire plant is devoted to this function. The "body" of the plant is divided into two succulent leaves fused together in the shape of an inverted cone. The fissure or slit at the top of the plant is the division of the two leaves. There is no stem as such, but rather the taproot joins abruptly at the base of the leaves. The structure of the plant reveals to the imagination the harsh environment in which Lithops live: the scarcity of water demands that young plants limited to only two leaves and a root system, as more extravagant growth would only serve to waste water. The leaves are thick to store enough water for the plants to survive for months without rain. The plants are small and keep a low profile to minimize the effect of the intense heat and light of their climate.
The above information can be taken into account when growing Lithops in the home or greenhouse. Because they thrive in low humidity and need infrequent watering and care, they make ideal houseplants, providing the conditions of adequate light and proper watering are met. Care must be taken to select a well lit location for the plants. Because they have adapted to intense sunlight in the wild during their evolution, they need a good amount of direct sunlight when grown as houseplants.
Lithops do well if they receive about 4 or 5 hours of direct (or only slightly filtered) sunlight during the early part of the day, and partial shade during the afternoon. Usually a southern window is the best location, unless it exposes the plants to full sunlight most of the day, which should be prevented. An unobstructed eastern exposure is a good alternative. A window facing west may be suitable, although not ideal, and of course a north facing window offers no direct sunlight at all.
If the plant do not receive a certain amount of direct sunlight for a few hours a day (when the weather permits, of course), they begin to grow slender and elongated, leaning to one side to receive more light. They also lose coloration and the sides of the plants turn greenish. They will eventually die if better lighting is not given them when these signs become evident. In some situations however, it is advisable to shade the plants a little from intense sunlight in the spring to prevent sunburn, especially in areas that experience poor light during most of the winter. This is because the plants lose resistance to bright light during a prolonged period of overcast weather, and the sudden brightness of a clear day will cause them to become burned, causing a whitish scar tissue to form on the surface of the plant. A badly burned plant may be so severely injured that it may die. This is why you should expose the plants to bright light gradually over a period of several days if they have been in dim light for some time. This is especially true of newly purchased plants.
Some growers provide protection against possible sunburn as early as April. An ordinary window screen should be adequate for this purpose. It would be best to remove the protection during winter to give the plants more light. If the plants get good light in the winter, you shouldn't have to worry about the chance of sunburn damage occurring in the spring.
Watering is another important consideration that must be taken into account. Lithops have a definite yearly cycle of growth. While it is important to water at only certain stages of the cycle, it is just as important to keep the soil dry at other stages of their growth. Do not become discouraged if the suggestions for watering seem lengthy and confusing at first. As you became aware of how the growth cycle operates, you will find that knowing when and how to water the plants is actually a simple procedure.
Lithops are perennial plants which develop a new pair of leaves each year. The leaf markings of any one particular plant change very little from year to year, and no two plants have markings exactly alike. Lithops begin growing during the fall, continue throughout the winter and into the spring. In late spring or early summer, the plants will begin to go dormant. In habitat, it is necessary for their survival to rest during the long period of intense heat and little or no rainfall, using what water they have stored previously to last the summer. With the approach of cooler and shorter days of the fall, Lithops will grow again.
Fig. 1) During the summer months, Lithops become dormant, resting as they do in the wild, although as a houseplant the conditions are not so severe. The plants require little or no water when they are dormant. Regular watering during this period would almost surely cause them to suddenly rot and turn into mush. But if a prominent shrivelling occurs during the summer, it is safe to give just enough water to restore the firm appearance of the plant. Water lightly so that about only the top one-half inch or so of the soil is moistened. Never water deeply when the plants are dormant.
Fig. 2) In the fall, usually in August or September, the plants will begin growing. The first sign of growth is noticed when the fissure between the leaves begins to separate. In the days to follow, a bud will force its way up through the fissure and shortly thereafter a white or yellow flower will unfold. The flowers of many of the Lithops species have a spicy-sweet scent. If a plant does not flower the first year, perhaps it is not quite old enough. Lithops usually must be three to five years old before they begin flowering: they have been grown as seedlings for two years or more in the nursery. As the fissure separates further, a new pair of leaves can be seen developing inside. As the plant becomes older, it increases in size by division. This will begin by one plant producing two pairs of new leaves. The plant will then have two "bodies" attached to one root system. Some plants in Lithops collections have as many as ten or more bodies per plant, but it takes many years to develop a plant of this size.
In the wild, Lithops begin to flower and grow just after the seasonal rains have begun **. In cultivation, watering should generally begins from early to mid August for most species. Often a good drenching of the soil will encourage the plants to begin their growth cycles. It is safe to water deeply during the fall, and in fact is better than a shallow watering because the plants have taproots. It is important to let the soil dry out quite a bit between waterings: it should not still be wet when you water again. The soil mix should be a type that drains quickly and dries out relatively fast. A soggy soil remaining around the plants for days must be avoided to prevent rot. Regular waterings should be steadily decreased after the flowering period. Discontinue watering altogether by about late September for most species to allow the soil to dry out completely in preparation for the cold winter months.
Fig. 3) During the winter months, the plants will still be growing; the new bodies will be increasing in size as the old outer leaves begin to shrivel. No water at all should be given during the winter … the soil should remain bone dry no matter how shrivelled the plants become. The new body actually draws out the water stored in the old leaves to continue growth, so do not remove the shriveled leaves. Lithops should not be exposed to temperature lower than 40°F (5°C). If the plant are too near a window during freezing weather, they will be damaged by frost even though the room seems warm, so move them back a little during really cold winter weather.
Fig. 4) The new body continues to extract the water and nutrient stored in the old leaves until the old leaves are reduced to nothing more than thin papery shells. These shells can then be easily removed from around the plant. It is spring by the time the plants reach this stage, and it is safe to water again to let the plants increase their growth. Begin by watering lightly, increasing the amount of water gradually, working up to several good drenchings during mid spring. Be sure to let the soil dry between waterings. Reduce watering as the heat and long days of summer approach, allowing the plants to prepare for their dormant period.
This brings the discussion of the growth cycle of Lithops full circle. It should be noted that this serves only as general guide to the way that Lithops grow. Each species has its own timetable for completing each stage of its growth, and it is nearly impossible to alter. Some species bloom as early as July, others as late as November. Although the method of cultivation described above is suitable for all species, you may wish to vary the times of watering a little as you become experienced in recognizing the different habits of each.
An ideal setting for Lithops is a group planting in a dish garden, intermixed with rounded stones of varous sizes and colors. The plants then display their nature of mimicry to the fullest as they become almost indistinguishable from the pebbles at a glance. Pots that are about 3 – 5 inches deep are recommended to allow the roots adequate room to grow. Make sure that drain holes are provided for the pot. Use a quick draining soil mix (a packaged soil mix for cactus and succulents should have sand added at the rate of about 2 parts soil mix to one part sand by volume). Space the plants at random, poking a hole into the soil to accommodate the taproot and lower portion of the body. Position the plants in the soil so that about three-quarters of the height of the plant remains above the soil level to permit the plant to „breathe“. Collapse the hole around the taproot by carefully poking a pencil into the soil near the plant. Set a few pebbles among the plants and finally sprinkle a thin layer of coarse sand (or bird gravel) over the exposed soil. Some of the plants will actually seem to have disappeared from sight among pebbles. (Note – planting Lithops in terrariums is not recommended due to extreme humidity).
Spider mites are troublesome pests that sometimes attack Lithops. Their small size often lets them go unnoticed, but the damage that they cause can be seen as small spots of white scar tissue on the surface of the plant. Any insecticide used for the control of mites that is safe for most houseplants can be used at the recommended rate per label directions.
Concern has arisen in recent years about the hazard that toxic houseplants represent to small children. Lithops are non-toxic. In fact, literature makes reference to children of several African races sometimes eating these plants as a means to quench thirst ***. It should be stressed however that any non-poisonous plant becomes toxic for a certain time after insecticides have been applied.
* Cole, D.T. Lithops in habitat (Lithops p. 24) ** Dugdale, C.B. Lithops: Their structure and growth cycle (Lithops p. 19) *** Cole, D.T. Lithops in habitat (Lithops p. 29)