Bursera fagaroides, "Mexican Frankincense" - Cactus Club

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Bursera fagaroides, "Mexican Frankincense"

Plant of the Month > Species A to B


by Bruce Brethauer

Over the years, I have grown a wide variety of succulent plants, representing many genera and curious growth habits, but I have only grown a few of the so-called pachycaul plants. Pachycaul refers to a growth habit in which the main stems and branches of plants are modified to store water and nutrients to help the plants survive periods of drought. This term is usually applied to woody species, and typically is reserved for species which are only moderately succulent: Pachycauls in general have the appearance of a basic shrub or tree with an extra thick trunk and main branches: they are especially favored by bonsai enthusiasts because these plants typically produce a nice, thick trunk and heavy branches early in their development.

               This month’s plant of the month, Bursera fagaroides is a fine example of a pachycaul plant; it produces a very thick, short trunk, topped with a few main branches which typically spread horizontally. The trunk and main branches are of a grey-green coloration and are covered with a smooth bark which peels off in parchment-like sheets. To my eye the trunk and main branches have the appearance of a large, grey-green, overstuffed sausage. Thinner (non-succulent) stems are produced on top of the main branches, and these are spreading to upright in habit, eventually growing to heights approaching 20 feet. New stems emerge a purplish-mahogany color, eventually maturing to grey–green. The individual leaflets of the compound leaves are small, oval to lance shaped, and toothed along its edges, looking very much like the leaves of a beech tree (the specific name of this species, fagaroides, is a reference to the beech tree family, Fagus)

               True to the common name of this species, (“Mexican Frankincense”) it is related to Frankincense tree (Boswellia sacra). True Frankincense is native to Yemen, Oman, and Somalia, and is adapted to conditions of both low rainfall and very high temperatures (which frequently soar to 120 degrees Fahrenheit and more in habitat). While the true Frankincense is difficult to maintain in cultivation, Mexican Frankincense is comparatively easy, tolerating a wide variety of growing conditions. Where it is happy, Mexican Frankincense is a fast grower, with each stem producing multiple branches, each of which may grow 12 inches or more in a season, and the trunk and main branches growing noticeably thicker with each year. One of my favorite traits of this plant is the rich aroma it produces when the plant is disturbed, or its leaves are crushed – it resinous scent is little short of intoxicating. Its dried sap has been employed in incense, and medicinally, to relieve congestion, and to strengthen the immune system (much like true Frankincense).

                Mexican Frankincense is easy to grow, provided that you cater to a few of its specific needs. It grows best during the heart of summer when light is particularly intense, and temperatures are high. I have found that unless you have a greenhouse or a very sunny Florida room, it is best to grow this plant outdoors in the full sun from mid May through the summer months, to benefit from increased sunlight and warm temperatures. Even though this species will regularly experience temperatures above 100 degrees in habitat (it is native to the extreme southwestern corner of Arizona and south, well into central and western Mexico), our summer temperatures, averaging between the mid 70’s to the high 90’s appears to be warm enough for it to produce good growth. It is my impression that without this period of warm temperatures and bright light, this species will not thrive – it is not really suited for a year-round existence as a houseplant. It is also an opportunistic grower, producing new growth whenever conditions are to its liking, so whenever it is provided warm temperatures, bright light and evenly moist soil, it will produce a new flush of growth. Conversely, it will rapidly drop most of its leaves and become dormant in response to conditions which are not to its liking, particularly excessive drought, excessive heat (which is not likely to be a concern when growing this plant in Ohio) or excessively cold or unseasonably cool temperatures. Even though this plant is adapted to very dry regions, and can easily survive extended drought, if you want it to produce particularly rapid growth, make sure that it does not experience extended drought during the summer months, (which will induce leaf drop and dormancy). Because it is such a rapid grower, it will require a bit more fertilization than most other succulents. I fertilize mine every month in summer with a low nitrogen, liquid fertilizer, mixed at about ½ the recommended strength, with little or no fertilization throughout the rest of the year.

               Mexican Frankincense will eventually become a large plant; even so, it can be kept compact with  extensive annual pruning. I usually prune my plant in early spring, just as my plant is breaking dormancy. I am ruthless with my pruning, cutting back the previous year’s growth to about an inch or two. Not only will this keep the plant compact, but it also encourages branching, producing a less gangly looking plant. True aficionados will object that my plant does not have the typical growth habit of a plant in habitat, but I am trying some bonsai techniques, which I hope will eventually produce a plant with the general appearance of a miniature Baobab tree. Pruning releases copious amounts of milky sap, which emits a heady fragrance. Sometimes the sap will congeal into small globules of resin which may be harvested and added to incense or melted and added to candle wax to produce a distinctively scented candle. You may also try to root a few of the pruned cuttings to propagate additional plants. Many growers insist that this plant is easily grown from cuttings, but this has not been my experience – I have tried to root hardwood cuttings (taken in spring) and softwood cuttings from new summer growth, and neither time did I manage to get any to root. I am trying a different technique, called air layering, which attempts to produce rooted stems while the stems are still attached to the plant: a stem is nicked with a sharp knife or blade, and is treated with a rooting hormone, and is then wrapped with sphagnum or other rooting medium, and is then wrapped in polyethylene plastic to maintain high moisture. I expect that this will result in a good number of rooted cuttings in months to come – time will tell.

               When temperatures drop to nearly freezing in fall, I finally bring my plant indoors to a very cool area: any cool, frost free area will do; breezeways, Florida rooms, a chilly alcove or a cool basement or attic (I keep mine in the basement, where temperatures may dip to the low 50’s in winter). The cooler temperatures should induce this plant to drop practically all of its leaves. By maintaining cooler temperatures, and keeping the soil dry throughout the winter months (giving only an occasional light watering to prevent root loss), this plant should remain dormant throughout the winter months. Monitor it throughout the winter – if the dormant buds appear to be too dry, you may need to increase the frequency of watering, but if it is breaking dormancy, and producing new leaves, it may need to be kept drier and a bit cooler to prevent it from growing at this time. If you can provide optimum growing conditions throughout the year, (if you can provide greenhouse conditions in the winter) then it is possible to grow this plant without a winter dormancy: growers in warmer parts of the country report that they can maintain year–round growth in their plants without ill-effects, although some growers suspect that a dormancy period may help facilitate the production of flower buds. I increase the frequency of watering in early spring to encourage my plant to break dormancy, and move it to a warmer spot with as much light as I can possibly provide. It usually begins to show signs of growth by the time that outdoor temperatures have warmed enough to move it outdoors. I gradually acclimate it to the increased light levels by moving it to ever brighter positions outdoors until it is in full sun for most of the day.

               Bursera fagaroides is distinctive for its smooth trunk and main stems; its attractive peeling bark gives this plant additional interest. It is one of the easiest and one of the most attractive members of the Bursera genus. In addition to its attractive appearance and distinctively swollen stems and branches, I especially like this plant for its fantastically scented resin. Not only is this a comparatively easy plant to find in the trade (a number of specialist nurseries carry plants of this species), but it is one of the easiest, and most forgiving species of the Frankincense family. This plant may not be for all growers–it can eventually grow to a fairly large size, and requires particularly bright light during the summer months for optimum growth, but with these concerns aside, there are few other plants that combine its distinctive appearance, relative ease of care, and its wonderfully scented sap. If you have never grown a pachycaul plant in the past, this would be an excellent plant to begin with.

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