Flowering Stones & Mesembs
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Lithops N.E.Br
Lithops gesinae C207 and L. julii C64
Even if they all look alike, broadly speaking, not all species in Lithops behave alike. The differences involve soil preference, sensitivity to an overabundance of water and heat, flowering times, and rapidity of shrinking and sheathing. Most species will grow in any well-drained mixture, but a few, especially those in the L. comptonii complex, do best in a very firm humusless mix. These species are also the most rot-prone. All lithops will grow and thrive in deep or shallow pots; of course the available depth will affect root length, one's watering regime, and the ultimate size of the plants.
Most species receive summer rain in habitat, but there are some which are wet in winter and others which come from areas of erratic and very sparse rain. However, in cultivation all lithops without exception send forth their new heads by summer. That this is not merely a “cultural bias” is demonstrated by the behavior of seedlings. Whenever sown and however watered, seedlings eventually conform to a cycle in which they begin to expose their new heads in late winter. By summer they are ready to grow, though here we face an old semantic problem. The visible expansion of heads take place in spring and summer; but their formation occurs in winter, and even though this amounts to a usurpation of the old body's resources, it can still be termed “growth.”
L. pseudotruncatella and its variants flower in early summer, while the northern forms of L. optica (including 'Rubra') flower in mid-winter. The other species fall into the main yellow group, flowering in late summer to early fall, a few late yellows (L. olivacea and the original form of L. naureeniae), and the great white wave, which normally occurs weeks later than the main yellow one. If an adult lithops does not flower, this is not merely a disappointment for the plant: it can also impair its health, since the initiation of floral and vegetative buds is normally a twinned process. (Often the flower bud aborts at an early stage; nonetheless its surviving “twin,” the new head, will emerge normally.) It is wise to water lithops generally in summer to encourage buds of both kinds. I also water them in winter, to encourage the emergence of new bodies, but this watering is very shallow and selective, and it is superfluous or destructive where winters are dank.
Some dormant lithops make a complete sheath a la Conophytum, with only a small “air-hole” at the fissured apex. Others send forth their new bodies in a rush, and the old ones gradually wither away. This behavior is usually consistent within a species, the white-flowering ones having thicker leaves and a later ETA. If the transfer of resources from old to new goes well, the new bodies should look plump and unwrinkled; they only need a proper watering when the takeover is complete, or when they look wrinkly. If a lithops does not shed its skin by summer, it either lacks a meristem (in which case it is effectively brain-dead) or it has decided to re-use its old leaves. In that case the plant will probably survive, but it will look very weather-beaten during its prolonged sabbatical.
Lithops can be propagated from cuttings exactly as with conophytums, though rooting is slower and less certain. However, I only take cuttings of lithops which are exceptionally pretty, as they are so easily reared from seed. When pollinating lithops, you can either employ all the clones at your disposal, in an effort to reproduce the whole visible spectrum of characters, or you can mate the two most similar seedlings. This practice of refined selection, in which plants are re-selected for an intensified pattern over several generations, yields fantastically attractive specimens and it surprises me that so little of it has been done. Along the same lines, you can attempt to self a particularly good specimen and then mate its progeny. To self-pollinate a lithops, use Conophytum herreanthus pollen or simply apply a brush on several successive days.
Many hybrids within the genus are possible but most of the ones I've made are dull or ugly or both. A few have interest because they closely resemble wild species (e.g., L. gracilidelineata × L. vallis-mariae “=” L. pseudotruncatella 'Pallid form'), and a very few are really pretty (e.g., L. pseudotruncatella × L. bromfieldii). Hybrids across the “subgeneric” (i.e., the white-flowering vs. yellow-flowering) barrier are possible in the L. marmorata and L. olivacea groups, and also in L. herrei × L. optica, but the latter two probably comprise one species anyway. Hybrids with conophytums are possible but the seedlings are exceedingly weak and not promising. (However, L. steineckeana is probably a conopops, and it is indecently sturdy.) ×Dinterops is discussed under Dinteranthus.