I have been growing Mexican Frankincense (Bursera fagaroides) for many years now. The plant is a pachycaul shrub/small tree, producing thickened, moisture storing trunks and primary limbs almost from the start, which gives even a young plant a “natural Bonsai” appearance. The crushed leaves and sap of this species is highly aromatic, with an exotic resinous scent which is little short of intoxicating. The common name suggests that the scent is similar to that of the Biblical frankincense, and as it turns out, the dried resin is used in similar ways, both as an incense, and medicinally (the resins of many related species show antibiotic and anti-inflammatory properties). The similarities are more than superficial; as it turns out, Bowswellia sacra (one of the sources of frankincense) and Bursera fagaroides are actually related, belonging to the Torchwood family, a group which includes 15 to 17 genera with over 500 species of woody flowering plants, including all of the plants discussed here. Not all of the members of this family have a pachycaul growth habit or produce highly fragrant resins, but there are a good percentage of these plants which do.
Our recent association with the Bonsai Society, and the increased availability of various species of the Torchwood family has piqued my interest in growing a few additional species. Time will tell whether all of these plants are good material for bonsai, and for that matter, I do not know how soon or how large the pachycaul growth is in each species, so I expect that some will take longer than others to produce a hefty trunk.
Bursera fagaroides Mexican Frankincense: Over the years, I have grown and propagated over a dozen plants. I allowed my first plant to achieve nearly shrub-like proportions and eventually sold it, but not before I had propagated plants from seed and cuttings from the original plant to establish new plants for my collection, and for trade. One of its “daughter” plants is flowering for its first time this year, so it may be possible for me to start a 3rd generation soon. I have found this plant to be easy to grow and is very forgiving. It produces its best growth in the heat of summer in full sunlight, so I move my plants outdoors in spring, and bring them back indoors in fall prior to the onset of frosts (it will tolerate a few degrees of frost however). In conditions of extreme drought, extreme heat, or maintained at very cold temperatures, this plant will drop most of its leaves, but maintained in moderate conditions, it will retain at least a portion of its leaves all year. In fall, when I bring my plant indoors, it does shed about half of its foliage – probably in response to the reduction of light. In summer, I water this plant regularly – I allow the soil to become nearly dry between waterings, but to maintain strong growth, I do not subject it to extended drought at this time. If you want to produce particularly pronounced, pachycaul growth, water it less frequently, even in summer. I also regularly fertilize my plants in summer, giving them a very dilute dose of a lower nitrogen, bloom booster fertilizer (not necessarily to induce flowering, but to promote stronger growth of roots and stems) – nitrogen promotes unnaturally lush growth of foliage in succulent plants, so I choose fertilizers with low nitrogen and higher proportions of potassium and potash which are particularly beneficial for the growth of roots and stems. In summer, I fertilize about once every 2 to 4 weeks, but make very dilute applications – at about ¼ the recommended application rate or even less. During their winter dormancy indoors, I keep these plants much drier, and cooler (the temperature in my 3-season room varies from highs in the 60s, to lows in the lower 40s). At this time, I water no more than about once every 3 weeks or so; also, at this time, I do not apply any fertilizer. My seed grown plants quickly produced very thickened trunks and lower limbs, which rapidly gives them the appearance of a bonsai. The new growth is a purplish mahogany color, but as it ages, the bark turns to a grey color. Older limbs are covered with a thin, exfoliating bark which peels and flakes off in very thin, parchment like strips to reveal pale greenish trunks and branches. While the main trunk and older branches have a definite pachycaul appearance, new growth tends to grow very thin and long, so to keep the plants more compact, it is necessary to periodically prune the excess growth from the plant. Whenever you prune this plant, it fills the area with its heady, resinous scent, while I love this scent, some people may find it a bit overpowering, so a bit of ventilation may be called for when doing significant trimming. Many growers insist that this plant is easy to propagate from cuttings, but this does not reflect my experience – the majority of my cuttings fail to root and eventually perish, (although I have managed to root a few cuttings over the years). In the years that I have been growing this species, I have not seen any significant insect problems; occasionally, plants in their winter dormancy indoors may have issues with whiteflies, but these are easily controlled by making occasional sprays with very dilute, soapy water, and are not much of an issue.
I expect that most of the plants discussed here will require similar conditions, although the Commiphoras and Boswellias are probably less tolerant of cold conditions and will need to be brought indoors earlier in the fall – possibly even before the temperatures drop to 45 degrees; they may also benefit from warmer conditions during their winter dormancy – with temperatures above 55 degrees(?) Some of the new plants are showing evidence of iron deficiency, so I have recently included an iron supplement when I fertilize them: an old timer’s trick of including a rusty nail in the pot when potting these plants may also be beneficial as a preventative measure. I have only begun to grow the following species this year so it is too early for me to make additional generalizations on the care on these plants.
Bursera hindsonia, Red Mexican Frankincense: This is Native to the Sonora and the Baja peninsula in Mexico. It appears to have many of the traits of B. fagaroides, including a fast growth rate, and the development of pachycaul growth from the start. The bark is reddish brown on new growth, which becomes greyer with age, but the bark does not exfoliate. The leaves are larger than those of B. fagaroides, and my experience suggests that it requires more iron in the soil, so I have recently started including an iron supplement with its fertilization. The scent of the crushed leaves is similar to those of B. fagaroides, but have a somewhat sharper scent with notes reminiscent of rubbing alcohol.
Bursera microphylla, the Elephant Tree: This is perhaps the northernmost species of Bursera; its range extends into southernmost Arizona and California, and south into northwestern Mexico; it is probably more adapted to arid conditions than other Burseras, so perhaps it would be best to water it less frequently than my recommendations for B. fagaroides. So far, its rapid growth and early development of pachycaul growth is very similar to its close cousin. The scent of its bruised leaves is also very nearly identical, and like its cousin, it also produces exfoliating bark. It has the most attractive foliage of the Burseras that I now grow. The leaves are reminiscent of the fronds of some ferns, and are particularly similar to, but much finer than those of the maidenhair spleenwort. The new growth on my plant appears to be more spreading and horizontal than the new growth of my B fagaroides. I don’t know if this is typical of the species, or just represents the current state of my one plant.
Time will tell, but I have the feeling that this species may be the most attractive plant and most suitable of the Burseras for bonsai.
Commiphora wightii, the Indian Bdellium Tree, Guggul: Native to southern Pakistan and northwestern India; the resin has been used as an incense and in Vedic medicine for over 3000 years. Overharvesting and habitat degradation has significantly reduced the numbers of wild plants, but this species is widely cultivated outside of its native range. Because plants flower and set seed while quite young, and the plants are sometimes self-fertile, this is one of the most readily available of the Commiphoras – and is touted as one of the easiest of the Commiphoras to grow as well. It produces nice pachycaul growth, and has interesting exfoliating bark. Arid Lands Nursery suggests that it will make a nice candidate for bonsai, but the plant is thorny, so it may not be a good choice for every grower.
Commiphora africana, African Myrrh: This species has a large natural range, which extends from tropical eastern Africa, south through Mozambique. Its resin is widely harvested as bdellium and myrrh – but whether or not this is the source of the biblical myrrh is hard to say. This too forms a large shrub/small tree with pachycaul growth, and peeling bark to reveal the underlying reddish color of the trunk and main branches; it is also a rather thorny plant as well. The leaves are produced in clusters of 3 (trifoliate) with the terminal leaf being larger and somewhat teardrop shaped. The bruised leaves are said to be pleasantly aromatic, but because my plant has only recently begun to produce new growth, I will let it grow out some more before I sacrifice a few leaves to test their scent. Once this plant begins its growth cycle, it appears to be a fast grower. Wikipedia suggests that this plant responds very quickly to increased humidity to initiate its growth cycle, but once it is subjected to drought conditions it soon defoliates and goes dormant. So, to maintain a longer growth cycle, do not subject this plant to drought conditions during its summer growth spurt. This plant appears to be easy to grow, but it is hard for me to judge the development of its trunks and branches, as my seedling appears to be pretty much uniformly twig-like so far.
Boswellia sacra, Frankincense: This is the primary source of frankincense in modern times, and may also have been one of the sources of frankincense in biblical times, although one source suggests that a closely related plant, Boswella neglecta, sometimes called B. asplenifolia is the primary source of the biblical frankincense. It is native to Oman, and Yemen in arid woodlands, but it is most prevalent in Eastern and northern Somalia. Over the years, this has been a particularly difficult plant to find in the trade, and has always commanded very high prices; in recent years, it has become increasingly available, and the prices have come down, although these are still somewhat more expensive than the other plants discussed here.
I have only recently acquired a seedling of this plant, and it is only now producing new leaves, so it is premature for me to comment on how difficult or easy it is to grow here. Many years ago, I was told that this plant requires especially high temperatures for best growth, so it must either be moved outdoors or in a greenhouse to produce normal growth. It also requires extremely bright light to thrive – preferably in full sun. It will probably require especially sharp drainage, as this species seems to be adapted to grow on well-draining soils on steep hillsides.
All of the plants discussed here, and many others, are discussed briefly but nicely illustrated with multiple photographs – usually including pictures of plants in cultivation as well as images of plants in habitat at Bihrmann´s Caudex.- Bruce Brethauer