Central Ohio Cactus and Succulent Society

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 3^rd 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

Bursera fagaroides

You either hate Kalanchoe diagremontiana or you love it. Or perhaps both simultaneously? I fall into the later category. Kalanchoe diagremontiana (from here on called K.d.) is one of the easiest succulents for a beginner to grow and propagate. It also has some very interesting flowers if you grow it well and let it get exposed to decreasing daylight hours of the winter. (It is called a short-day plant, that is flowering during the fall and winter as day length decreases.) At the same time, this plant, if not weeded out and removed from your “greenhouse” can easily take over.I was first introduced to this plant and began growing it in 1973. At that time, Kresge Department Stores (eventually to become K-Mart) often sold them at the cash register and in their plant section of the store. There would be a long hanging cardboard card with numerous small plastic bags pinned or clamped to the cardboard. You ripped a bag from the cardboard and paid for it at the cash register. Can’t remember exactly what they called them at the time, but the bag contained a single leaf with the instructions to safety pin the leaf to curtain in a sunny window of your house. The leaf would eventually sprout dozens of baby K.d.s which you could plant into soil containing pots. 

Now you were in possession of this incredibly invasive but fascinating plant!

In the seventh grade of middle school, I volunteered to take care of the school’s greenhouse. As soon as I walked into the greenhouse for the first time, the whole greenhouse was completely grown over with K.d. They were quite large, 3 to 4 feet tall. The biology teacher had purchased some Venus flytraps and I had to make room for them in the greenhouse by ripping out some of the K.d. That was the first time I realized how easily this plant propagates itself even under the most severe neglect. (Nobody watered the plants all summer when students or teachers were not there.)

This plant grows up as an upright stalk with triangular dark green leaves that look like the head of an alligator (hence one of its common names) (See photo). The leaves can be up to about four inches long, and as I mentioned previously, the plant can get up to three to four feet tall. Especially two-year-old plants that are subjected to the natural decreasing daylight hours of late winter. Starting in the fall, these two-year-old plants begin to elongate and get taller. Then in the middle of winter they produce umbels of hanging pinkish to red tubular flowers. (See photo) If you have different clones of this plant (rarely you do) then these flowers could get pollinated to produce seed. 

The seed, like other Kalanchoe species, is very tiny, almost dust-like. I have never grown the plant from seed. The usual mode of reproduction of this plant is via tiny baby plants that appear on small nodes along the leaf margins. There are many other Kalanchoe species which also propagate or reproduce this way. These tiny baby plants are clones of the parent. They grow several tiny roundish leaves and begin to put out small hairs of roots. If anything brushes or bumps into the plant the babies are dislodged from their nodes and fall to the ground. They quickly root and take off growing. In no time there are dense stands of this plant.

This species is originally from Madagascar where there are many other species of Kalanchoe. The plant has been distributed as an ornamental in many countries due to its interesting habits. In warm subtropical or tropical areas, they can establish outdoors and become invasive. They have escaped gardens in States like Florida. K.d. is very susceptible to frost so it is never established in northern areas that are subject to any freezing.

This plant is amazingly easy to grow for succulent enthusiasts. If you furnish it with plenty of light and remember to water it once in a while it will flourish. It is amazingly free of pest and diseases. Usually, the only problem I’ve seen is, they can get powdery mildew with inadequate light and ventilation (stagnant air). Powdery mildew will grow as a fine grey dust in circular spots on the leaves. If this happens it’s a sign you need to supply more illumination and increase ventilation. The mildew spots will sometimes be callous and heal over leaving unsightly brown corky spots on the leaves.

A while back I encountered another problem on my K.d.s. I had several of them develop curly and deformed leaves and stems. The damage was reminiscent of other succulents when they get infected by burrowing mites. I really didn’t care if they had mites since I have many plants and if the mites didn’t spread to my other plants. I eventually sprayed with systemics for mites anyway, but this didn’t take care of the problem. Then somewhere doing a literature search I found a reference that said these K.d.s are subject to deformities if they have nutrient deficiencies. I quickly found out that the deformed plants were simply not getting enough nutrients (fertilizer). Fertilizer applications seem to have taken care of the problem.Another reason for this plant’s success and invasiveness is it contains bufadienolide cardiac glycoside poisons, one of which is called diagremontianin. These toxins are very poisonous to cattle that might graze on this plant in semi-desert environments. This poison is probably why you don’t see animals and perhaps insects feeding on it. Slugs can be an intermittent problem in my greenhouse, but they never touch the K.d.s. Perhaps because of this toxin. So, if you have animals in your house like cats or dogs that like to dine on your plants, this may be one to avoid. Although I’ve never known anybody to report a problem with their animals from eating this plant. In fact, at one time I heard that land tortoises like to feed on it. Perhaps tortoises are immune to the bufadienolide cardiac glycosides?

With how easily this plant reproduces and propagates it begs the question, “Why doesn’t it take over in places where it grows”. Why doesn’t K.d. take over the subtropical and tropical world? Even though this plant is very aggressive colonizer in dry areas, I read it is a very poor competitor in areas that get enough rainfall to allow grass to grow. Seems that grass is K.d.s mortal enemy. If you like this plant a very close relative, Kalanchoe tubiflora, has similar growth and habits except its leaves are much smaller and simply spindle shaped or tubular. The baby Kalanchoe tubiflora grow only at nodes at the tip of this species’ leaves. Much less fecund that K.d. Sometimes these two species hybridize via cross pollination of their flowers and if you grow them from seed. Leading to plants that are intermediate in appearance between the two species. Older references placed these two plants in genus Bryophyllum. So, you may see them in these books listed under this genus rather than Kalanchoe. Another very popular Kalanchoe is Kalanchoe blossfelldianum. Commonly called Flaming Katy, Florist Kalanchoe or Christmas Kalanchoe. This species is sold as a wintertime or Christmas flower in many garden centers. It comes in many blossom colors such as red, yellow, and orange. This Kalanchoe does not reproduce by tiny babies growing at nodes. It is propagated by stem and leaf cuttings and by seed.

I hate K.d. because I must get into my greenhouse and weed them out. However, I also love them because they are so easy to grow, propagate so easily, and because they are obviously a well-adapted plant fit for survival.

The genus Kalanchoe has a huge number of very diverse and fascinating species (estimated to be 125).Enough to keep a succulent enthusiast busy collecting ever more interesting species of this genus. I would collect different Kalanchoes if it wasn’t for the fact, I already grow more cacti than succulents. I just need to get into my greenhouse to weed out the ever-present K.d.s that are always threatening to take over!  – Doug Sweet

The Gasterias (sometimes known by such common names as “Bow Tie Plants” or “Cow’s Tongues”) have been popular succulents for many decades for their ease of culture, their tolerance to relatively low light levels, their interestingly patterned foliage, and their many cultivars with beautifully variegated foliage. Many species, and many dozens of named varieties are readily available in the trade at reasonable prices, and most of these plants are reliably pest and disease resistant. Most plants are compact growers which can be maintained in smaller pots and planters for many years. While there are a couple of species (G. croucherii, and G. acinacifolia for example) which are much larger plants, and may eventually grow to several feet high or more, these are the exceptions to the rule: most species may top out at about 6 to 8 inches, and a few seldom grow much taller than a few inches. Practically every species has unusual arrangement of leaves in which the leaves are curiously stacked one on top of another in two ranks, (the proper term is that the leaves are “distichous”) giving rise to one of the common names for this genus, the “Bow Tie” plants – seen from above, the plants have a bow tie appearance. In some species, as the plants mature, they produce their leaves in a rosette, but many species continue to produce this “bow tie” arrangement throughout their lifetime.

These plants are closely related to Aloes and Haworthias, and many hybrids have been made between these groups (sometimes listed as “Gasteraloes” and “Gastwothias” in the trade). The trait which distinguishes the Gasterias is their unusual flowers, which are tubular with a noticeably enlarged bases and midsections. These flowers were regarded as stomach shaped, and
the genus was named Gasteria (“Gaster” meaning stomach) accordingly.
It is hard to find a consistent number of accepted species for this genus, as the species are highly variable, and all of the species can readily hybridize in habitat, making absolute IDs difficult. I have seen the numbers of accepted species ranging from about 2 dozen to about 50 species, depending upon the author. In cultivation, there are probably hundreds of named hybrids and cultivars. All of the species are native to Southern Africa, including Namibia, and most species typically grow in somewhat shaded conditions – usually in the shade of larger plants, or perhaps on the shaded side of hills and canyons. 

Gasteria rawlinsonii is perhaps the most distinctive species of the genus, and it is unlikely to be confused with any others. The species is adapted to growth on cliffs, and as a result, the stems typically hang over the edges; to our eyes, hanging “upside down”. Also, the stems can grow very long – one source indicates that the stems can grow to lengths of 6 feet or possibly even
longer, but given the slow rate of growth of the Gasterias, such plants would probably take decades to achieve these sizes in cultivation. Wikipedia offers the following information on its habitat and distribution:

This species is restricted to the Baviaanskloof mountains, in the Willowmore District of the Eastern Cape, South Africa. Here it tends to grow hanging on cliff faces in shady ravines, growing in well-drained sandstone soils, usually on the shady south-facing cliffs.

It is my understanding this species has such a restricted range that it is fairly rare in habitat, and that its cliff hanging habit makes it a challenge to collect plants and seed, so over the years it has been pretty hard to find plants for sale. On top of this, it is slow growing and divisions are only offered sporadically. I suspect that seed raised plants may take several years to reach a marketable size, so it may remain a hard-to-find item for some time. Even so, just because it may be hard to find, doesn’t mean that it is hard to grow, quite the contrary, like the overwhelming majority of Gasterias, this is a forgiving plant, tolerating a variety of growing conditions and soil mixes. While in habitat, it favors shaded habitats, and it is better adapted to somewhat lower light levels than most other succulents, in cultivation it is still best to give it bright but indirect light.

While most growers pot this plant on top of the pot and allow the stems to cascade over the sides, I have taken the more extreme measure; I have potted my plant in the drainage hole of a hanging basket and to let it grow naturally “upside down”. Its cliff dwelling habit also suggests that good sharp drainage is particularly important to this plant, so make sure that it is given a good gritty
mix, but also make sure that the soil contains essential nutrients – this plant cannot thrive in just grit and sand. I do a lot of composting in the garden, and have found that a succulent mix that includes a good amount of well-rotted leaf compost is particularly favored by many of my plants.

But lacking this, it may be a good idea to provide regular (monthly) application of a low nitrogen liquid fertilizer (dilute the fertilizer to about ¼ of the recommended application rate). I only apply fertilizer during the growing season (from the warmer months of spring through the early weeks of fall). While I have not paid much attention to the pH of my potting mix, the fact that plants in habitat typically grow on sandstone cliffs would suggest that this species is adapted to somewhat more acidic soils, so it may be beneficial to incorporate some peat moss into the growing medium as a soil acidifier (or water the plant with tea water from time to time). The occasional application of a commercial soil acidifier may also be beneficial – but always use such acidifiers in moderation, – as with fertilizers, it is usually best to dilute these to about ¼ of
the recommended application rate. When in doubt, use less. In its natural habitat, Gasteria rawlinsonii may receive anywhere from about 10 to 15 inches
of rain in an average year, and while this is considerably drier than Columbus, this is still moister than most desert habitats – do not water with a teaspoon or an eye dropper! When watering, Water it well, and during the warmer months, water it regularly, but make sure that the soil does not remain saturated for extended periods (if it does, it needs a more gritty potting medium). Let the potting medium become dry before watering again. Plants in habitat may receive rain in any season, but the majority of the rain falls during the summer months, as a result, this plant will produce the majority of its growth in spring and summer. But it can grow and flower through much of the year, suggesting that it is an opportunistic grower – growing and flowering whenever conditions permit. I choose to keep my plant cooler and drier through much of fall, winter and into early spring, and I do not fertilize my plant at all during this time. Because
daylight is in short supply at these times, I want to prevent any growth at these times to prevent weak and etiolated growth. When temperatures permit (when temperatures reliably rise above about 45 to 50 degrees) I move my plant outdoors into open shade to dapple shade – my front porch provides a good habitat for this. Later in the season, as it adapts to brighter conditions, I
may move it to slightly sunnier conditions – but I will never move it into full sun, as I fear that this may possibly scorch its foliage – any such damage will permanently mar the appearance of any affected foliage.

To date, my plant has not flowered, I suspect that plants need to sufficiently mature before they will regularly flower. My experience with other Gasterias is they they can be successfully self-pollinated, at least with a bit of assistance, so I am hopeful that when my plant flowers, I will be able to produce viable seed, and will be able to supply some nice seedlings in years to come.

Gasteria rawlinsonii is perhaps the most unusual and attractive species of the Gasterias. Its unusual cascading growth habit, and its unusually long stems makes it exceptional; a well grown specimen practically commands attention. Even though it remains fairly hard to find, it is not hard to grow. Like other Gasterias it is a forgiving plant, tolerating a good amount of benign neglect. It tolerates lower light levels than most succulent plants, it is possibly more pest free than most Gasterias (its well-spaced leaves do not conceal insects like some other Gasterias can).

I highly recommend this plant; it is my favorite of the genus. If you ever find one for sale, by all means, give it a try. – author Bruce Brethauer 

Gasteria rawlinsonii varieties – Kirstenbosch 6 – Gasteria – Wikipedia
Gasteria rawlinsonii – staircase 5 – Gasteria rawlinsonii – Wikipedia
Gasteria rawlinsonii-IMG 0692 – Gasteria rawlinsonii – Wikipedia