Boswellia Care Guide — Enjoying Frankincense Trees as Caudex Plants

Boswellia is a tree of the Burseraceae family that has been prized since ancient times as the source of "frankincense," and in recent years its popularity as a succulent/caudex plant (caudex) in horticulture has been soaring rapidly. Its appeal lies in the beautiful balance of the swollen trunk, distinctive bark, and small leaves, and it can be enjoyed in a bonsai-like manner. Here we explain the basics of growing Boswellia.

Boswellia Varieties and Characteristics

Approximately 30 species of Boswellia are known, but only a limited number of varieties are available in horticulture. We will introduce the main varieties.

Boswellia neglecta is the most readily available beginner species. Native to East Africa, it is characterized by smooth white to gray bark. Growth is relatively fast, and the trunk begins to thicken within a few years from seed. It is hardy and easy to care for, making it ideal for those attempting Boswellia for the first time.

Boswellia sacra is the most famous species as the source of frankincense. It grows naturally in southern Arabia and Somaliland, with beautiful silver-gray bark. While its growth is somewhat slower than neglecta, the way its trunk thickens has a dignified character, making it a variety popular with collectors.

Boswellia rivae is native to Ethiopia and has distinctive reddish bark. The trunk tends to become thick, and it is a variety with a beautiful caudex form. It is somewhat difficult to obtain, but its cultivation difficulty is roughly equivalent to that of neglecta.

Boswellia pirottae is endemic to Ethiopia, with a delicate impression from its greenish bark and small leaves. It is not widely available, but it is popular with enthusiasts for its unique atmosphere.

All of these varieties are plants that grow naturally in dry rocky areas and cliffs in the wild, and while they are resistant to dryness and high temperatures, they tend to be weak against excessive moisture and low temperatures.

Sunlight and Temperature Management

Boswellia is a plant that loves strong sunlight, and securing maximum light throughout the year is essential for healthy growth.

During the growing season (May to October), direct sunlight outdoors is ideal. Shading is basically unnecessary, and it can withstand the intense summer sun in Japan. However, during the rainy season, it should be managed under rain protection to avoid prolonged rain.

When grown indoors, place it by a south-facing window or ensure at least 12 hours of light with a grow light. Insufficient light will cause the branches to become leggy, resulting in an awkward appearance with wide spacing between leaves.

It is very resistant to high temperatures but weak to cold. Most Boswellia drop their leaves below 10°C and risk dying below 5°C. During winter, bring it indoors and maintain a minimum of 10°C or higher.

Overwintering is easy indoors with heating, but be careful of temperature drops at night when heating is off. The area near windows can drop below 5°C even indoors due to radiative cooling, so move it away from the window at night or insulate it with a foam box.

When moving it outdoors in spring, suddenly exposing it to direct sunlight can cause sunburn. Gradually increase the light over 1-2 weeks through "hardening off."

Watering and Soil Management

Watering Boswellia requires clear seasonal management that follows its growth cycle.

During the growing season (May to October, when new shoots are developing), water thoroughly when the soil dries out. The frequency is typically 1-2 times per week, but adjust according to temperature, pot size, and soil composition. Boswellia surprisingly likes water during the growing season, and excessive drying will halt new shoot development.

During the dormant period (November to April), significantly reduce watering. While some growers practice complete water withholding, it is safer to water lightly about once a month to slightly moisten the soil. If the trunk becomes extremely wrinkled, give it a small amount of water.

The soil should be primarily inorganic with good drainage. A basic composition is 3 parts pumice : 3 parts red volcanic soil (hard) : 2 parts kiryu soil : 1 part charcoal : 1 part vermiculite. Boswellia has finer roots than Pachypodium, so small to medium-sized particles are easier to work with.

A shallow, flat pot is best suited for bonsai-style cultivation. Deep pots tend to accumulate moisture at the bottom, increasing the risk of root rot. Slitted pots or terracotta pots are recommended for their superior drainage.

Shaping and Pruning

One of the great attractions of Boswellia is that you can shape it like a bonsai.

Pruning is done during the growing season. Cutting back overgrown branches promotes branching and creates a well-balanced canopy. A milky white resin (the source of frankincense) may ooze from the cut. This is what makes Boswellia uniquely interesting.

Wiring is also possible, but not as aggressively as with bonsai. Boswellia's branches are somewhat brittle, so wiring thick branches risks breakage. It is safer to wire young, soft branches or use guide wires to direct their growth.

To thicken the trunk, it is important to provide adequate water and light during the growing season and actively allow branches and leaves to develop. Cutting the branches too short reduces photosynthesis and slows trunk thickening. The basic strategy is to first thicken the trunk, then prune to the desired shape.

Seed-grown specimens are particularly prized for their beautiful trunk thickening and form naturally rugged caudexes when grown from seed. It is difficult to achieve a similar form through grafting or cuttings, so seed-grown plants are highly valued.

Enjoying the Frankincense (Resin)

One of the great pleasures of growing Boswellia is being able to harvest and enjoy frankincense from your own plant.

Resin may naturally ooze from well-established plants (trunk diameter of 3cm or more is the guideline). Making small wounds on the trunk promotes resin secretion, but keep wounds minimal to avoid damaging the plant.

The collected resin hardens when dried and can be burned as incense. Warming the resin over charcoal or in an incense burner releases a uniquely sweet, cool scent. Enjoying this fragrance that was sacred to ancient Egypt and Mesopotamia in your own home is a special experience.

However, harvesting large amounts of resin from horticultural seed-grown plants puts strain on the plant, so limit yourself to enjoying only small amounts. Prioritize growing a healthy plant long-term over harvesting resin.

Since Boswellia has limited market availability, br-choku is convenient for obtaining specimens with clear variety identification. You can purchase seed-grown plants carefully cultivated by breeders directly, and also receive variety confirmation and cultivation advice.