The Correct Method for Repotting and Root Pruning Lithops

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The best time to transplant Lithops seedlings or repot mature plants is in summer, when the old leaves are very wrinkled or completely dried out. If repotted too early in spring or early summer, the old leaves will likely absorb water and be unwilling to dry out, so they will coexist with the new leaves for much longer than normal. If repotted in late summer or autumn, Lithops are preparing to enter "dormancy" and do not easily grow new roots. When repotting, it is best to remove any remaining soft, wrinkled old leaves, as well as any completely dried skins and flower stalks. The former are usually very tough, so it is best to remove them with curved nail clippers; the latter are sometimes very brittle and may come off very easily, but usually still require scissors or nail clippers. Unless the flower stalk is very loose, do not pull it off casually, because it is too close to the Lithops growth point and may injure or even kill the plant.

Whether or not to keep the old skins on the plant is a common question that is largely a matter of personal preference. In their native habitat, depending on different climatic conditions, especially rainfall, the individual heads of Lithops will shrink down during dry periods and extend upward again after rain, which causes the lower parts of the old skins to fragment and the upper parts to loosen, and the shed fragments of old skin are blown away by the wind; or, in very arid regions, the old skins of Lithops will accumulate over many years (perhaps 50 years or more) into thick layers around the plant, especially between the individual heads. Keeping our Lithops as close to nature as possible means we do not need to clean away the dried old skins, but unfortunately mealybugs find old skins to be very attractive dwellings. The compromise is to remove the loose fragments that might provide nests for mealybugs, while leaving the very tight layers of old skin that mealybugs are unlikely to enter.

When repotting Lithops, we usually pinch off the tips of the seedling roots, and cut back the lignified main root and lateral roots of mature plants to a convenient length, but usually we cut until the white core of the root is exposed.

Sometimes, after a long dry period, the root system of Lithops will die back from the tips over a considerable distance; sometimes the roots are infected by white powdery fungus, which also causes the roots to die back and lose their ability to absorb water; sometimes the roots develop a thick corky outer layer. In all these cases, the roots need to be cut back until fresh white core tissue is exposed. If necessary, the roots need to be completely removed down to the base of the plant. The thick woody outer layer can also be peeled off with a clean, sharp knife or notched with cuts on the side of the root, so as to expose a small section of fresh core, and new roots will grow from the exposed core points in due course.

After root pruning, we can plant the Lithops in a new pot and water thoroughly immediately. If they are very dry, the plants will usually respond multiple times and swell up within 24 hours, presumably by absorbing water through the sides of the body and the cut roots. Over the next 2-3 weeks, before all the plants show obvious signs of having rooted and are growing by absorbing water, the soil should be kept moist but not waterlogged, which is usually best achieved by bottom watering. Frequent, even daily watering from the top also helps, especially in hot, dry climates. Once all the Lithops have rooted, the watering schedule can be normalized, gradually extending the interval between waterings until they receive the same treatment as the rest of the collection.

Sometimes individual Lithops will show signs of not having rooted after repotting; or, even in a tray with a stable root system that has not been repotted, especially after a dry winter, a plant may fail to respond to watering. Usually, "spot therapy" works at this point. The method is to slowly drip water directly onto that particular plant, letting the water penetrate down to the roots and below, but without making the soil of other neighboring plants in the same tray too wet. This requires daily drip irrigation, or even twice a day. (We use a medical intravenous drip set consisting of a bottle and a controllable drip tube, with great success.) In any case, if the spot therapy does not achieve the expected results after a few weeks, it is best to dig the plant out, cut the roots back a little more, and start rooting again; if the plant is in a tray with other plants around it, naturally the spot method is also used for rooting. You can also place plants that are reluctant to root in sand to root, then, without cutting off the newly grown roots, plant them back in their position in the tray, and use the spot method until the root system is stable.

In all cases, it is advisable to provide some extra shade for a few days to a week or longer after repotting Lithops. The pots or trays can be placed in a cooler spot than the usual top of the staging or bench, or covered with a frame fitted with shade cloth or wire mesh or plastic mesh. Plants in a tray undergoing spot therapy need to be given separate covers. Very effective shade devices can be made from X-ray film, cut and stapled into a suitable shape, leaving suitable ventilation holes. A cone of appropriate size with a ventilation hole at the top is a very satisfactory shade device.

The individual heads of a clustering Lithops can be separated by carefully cutting through the rhizome on which they grow; sometimes, an old plant whose long, weak root branches have grown up to the height of the individual heads may fall apart when dug out of the soil. Therefore, if you wish, or in order to share a particularly interesting specimen plant with other collectors, it is possible to grow these individual heads (or possibly pairs or small clusters of multiple heads) separately. However, it must be remembered that all these divisions are still part of the same plant, because Lithops cannot self-pollinate, and usually cannot produce seeds by pollinating one division with the pollen of another division. Generally speaking, there is no benefit to dividing a clustering plant; on the contrary, it is best to keep it intact and see just how big it can grow. Occasionally we are also asked whether it is possible to obtain two separate plants by cutting a single head through the middle gap! Doing so will almost certainly ensure the death of the plant.

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