by Bruce Brethauer
The "Rock Fig" is a remarkable plant, native to the Baja peninsula, Mexico: it is one of a few species of figs which are adapted to arid conditions. Young plants will produce a large caudex fairly quickly, providing the growing plant a moisture reserve. Later in its life, when the plant has produced a sufficiently large root system to provide adequate moisture for the plant, the plant invests less energy in growing the caudex, and the plant takes on a more normal appearance, with the base of the trunk only a slightly enlarged. The caudex of young plants can grow quite large, giving them a form reminiscent of the "Desert Rose" (Adenium obesum); the bark is of a grey coloration and smooth, and the leaves are heart shaped, and are fairly large. In some plants, the leaf petioles and midribs are an attractive pink to reddish color, adding additional visual appeal (in my plant, the petioles and leaf midribs are uniformly green). Habitat photographs of this plant reveal another interesting trait of this species - especially when plants are growing on rocky terrain; the roots often envelope rocks in complex mats and webs, and in time, the roots fuse together (anastomosed) creating root networks which look practically fluid. Many growers raise their plants to show off the thickened roots. Bonsai enthusiasts sometimes grow this species on large stones or rock slabs in the hopes that their plants will produce similar looking root webs. As with all Ficus species, the flowers of this species are microscopic, and are completely hidden within a fleshy receptacle (the so-called "fruits" of the fig family). to date, my plant has never produced fruits, so I cannot report on their size and general appearance, but in most Ficus species, the fruits are typically pretty non-descript and are generally inedible in most fig species: no-one grows this plant for its fruits or flowers.
My first encounter with the "Rock Fig" dates back to nearly 20 years ago: I was still new to growing succulents, and I was developing an interest in growing the caudiciforms, so I ordered a collection from the Glasshouse Works, and Ficus palmeri was included in that shipment. It was a small seedling plant - with a stem about 4 inches tall, and a small caudex, just under an inch in diameter. I made a lot of mistakes in growing that first plant, keeping it too dry for too long, and never moving it outdoors for fear that too much rainfall would rot its caudex. Under my care, this plant did manage to survive, but it never thrived, and barely produced any growth at all, growing only about 2 - 4 new leaves each year. I finally gave that plant away, hoping that another grower would fare better with it than I did. Do not repeat my mistakes: do not underwater this plant! Even though this species grows in very arid regions in habitat, many populations grow in riparian habitats, growing where their roots have access to more or less permanent water sources: when growing this plant in pots, especially when they are actively growing, they will benefit from frequent watering. In the heat of summer, I water my plant practically every day to achieve maximum growth! This plant loves summer heat, and thrives in full sunlight, so each spring - once all threat of frosts have passed, I move my plant outdoors, gradually acclimatizing it to direct daylight - moving it first to dapple shade, and gradually increasing its exposure to increased daylight. Without this acclimatization period, leaves and developing buds may become scorched; while this may not cause any permanent scarring, it can set growth back several weeks. Given a combination of full sun, long days, warm temperatures, and frequent watering, my plant grows at a remarkable rate. By the end of the season, each of the branches on my plant will have grown at least an additional 6 inches in length, and some may lengthen to 12 inches or more, and its caudex will have markedly increased in size - this year, the caudex of my plant may go from about the size of a tennis ball, to nearly the size of a baseball.
Such rapid growth will require extra fertilization - from May through August, I fertilize my plant with Miracle-Gro Bloom Booster (any fertilizer with a high phosphorous, and low nitrogen ratio will do) about once every week to 10 days. I dilute this to about 1/3 the recommended application rate, and give my plant a good drenching. In September, I discontinue the use of fertilizer, and reduce the frequency of watering, providing only enough water to prevent any signs of wilting. In fall, when I bring my plants indoors, I water this plant only about once every 2 to 3 weeks, and may reduce this to once every 3 to 4 weeks in winter. In the last 2 winters, I have wintered my plants under lights in my basement where temperatures regularly fall to the low to upper 50's. Given these cool and dry conditions, there is considerable leaf drop, but even so, my plant retained a portion of its leaves through every winter. In spring, about a month before moving the plants outdoors, I water this plant more frequently - about once a week to 10 days to encourage renewed growth. At about this same time, I also give my plant a severe pruning, cutting away all unwanted growth, and trimming back the remaining "new" growth to about 1 inch. This annual regimen of severe pruning will keep this plant more compact, and will typically result in a plant with a more massive caudex, and more "bushy" branching, with extra-thick main branches. Purists may argue that this growth is not typical of plants in the wild, which in time produces a less succulent looking trunk, eventually producing a trunk which is only moderately enlarged at its base. I argue that by keeping the plants more compact, I can grow this plant for many years before it outgrows my limited space: true, it may not look like a plant from Baja, but this isn't always my objective - this is one of those areas where my interests in Bonsai and Succulents has converged.
As with so many other succulents, the taxonomy of this species is in debate: in the past, the "splitters" considered this plant to be sufficiently different from its very close relative Ficus petiolaris to merit erecting the species Ficus palmeri. In recent studies, there is a strong trend to subsume F. palmeri back into F. petiolaris - treating it either as a variety or subspecies of F. petiolaris (and a few taxonomists would not even give it anything more than perhaps a forma or geotype status). I continue too call it by the name the old-timers would recognize.
This is another plant which was easier to locate in the past than it is now. I suppose that this is partly due to changes in taxonomy - some growers may now offer this plant as Ficus petiolaris, however, I believe that its present scarcity is due changes in the laws regulating trade in rare and threatened species, making it more difficult to export seeds and plants from Mexico. Growers in Southern California and Arizona occasionally grow this plant as on ornamental, and report that these plants regularly set fruits, and produce viable seed, so in theory, it is possible to propagate this plant from plants in cultivation in the United States; it is also possible to propagate this plant from cuttings, or by air layering. I am not certain if plants raised from cuttings will produce a typical caudex or not, but this is another technique to produce additional plants from plants already in cultivation. In time, I imagine that this will become a bit easier to locate in the trade, but at present, it is only available sporadically from nurseries specializing in succulents, caudiciforms, and bonsai stock.
Issues of availability aside, this is an interesting, and attractive plant. It is undemanding, and tolerant of benign neglect, but thrives best when provided with very bright light, warm temperatures, and adequate (and occasionally generous) amounts of water and fertilizer. Under favorable conditions, it is a fast grower, producing a large caudex, and a nice canopy of leaves. It is not for every grower: it does not produce large showy flowers, and its large, heart-shaped leaves may not make it suitable as a bonsai subject (where the smaller leaved species would be favored). But I am glad that I gave this plant a second chance, and sometimes wish that I had kept that first plant - after 20 years, I imagine that it would have become quite an impressive plant - despite my early blunders.