Propagating the Tree of Heaven (Androstachys johnsonii): A Gardener’s Guide
Introduction:
Androstachys johnsonii, commonly known as the Tree of Heaven (though unrelated to the Ailanthus altissima also carrying this common name), is a striking African tree prized for its beautiful, often weeping, habit and attractive foliage. Its distinctive appearance makes it a desirable addition to gardens in suitable climates, however, its propagation presents unique challenges. While its stunning form captures the hearts of many gardeners, its reproductive biology adds intrigue and complexity to its cultivation. Its popularity, coupled with the difficulty in propagating it successfully, creates a rewarding experience for those who conquer its propagation quirks.
Seed Germination:
Currently, there are no known reliable methods for seed germination propagation of Androstachys johnsonii. While seeds are produced, germination rates are exceptionally low, even under optimal conditions. Further research into specific seed treatment methodologies and environmental requirements is needed to ascertain if germination is even possible on a consistent scale.
Cuttings:
Cuttings offer a more promising, albeit challenging, route to propagating Androstachys johnsonii.
Challenges: Hardwood cuttings show limited success. The low rate of rooting is likely due to factors such as the tree’s physiology and the difficulty in maintaining adequate moisture levels within the cutting while preventing fungal infections.
Practical Tips: Semi-hardwood cuttings taken in late summer or early autumn, treated with a rooting hormone, and placed in a humid propagation environment with bottom heat (around 70-75°F) may yield a few successful plants. Misting regularly is crucial to maintain high humidity levels. A soilless mix, well draining and with high porosity for aeration, is recommended.
Rewards: Successfully rooting cuttings results in genetically identical offspring, preserving desirable traits of the parent plant. This is particularly useful for propagation of superior cultivars.
Division:
Division is not a viable propagation method for Androstachys johnsonii. This tree possesses a strong taproot system and is not easily divided without severe damage to the plant.
Tissue Culture:
Tissue culture offers the most promising pathway for large-scale and successful propagation of Androstachys johnsonii.
Challenges: Establishing a reliable protocol for in vitro propagation demands specialized knowledge and equipment. Finding the optimal media composition, growth hormones, and sterile conditions is crucial to prevent contamination and encourage shoot multiplication and root development.
Practical Tips: Employing standard tissue culture techniques, starting with nodal segments as explants, and employing growth regulators such as auxins and cytokinins would be essential steps.
Rewards: Tissue culture allows for rapid multiplication of elite genotypes, resulting in a large number of uniform plants within a short time frame. The method also presents opportunities for disease elimination.
Conclusion:
Propagating Androstachys johnsonii presents significant challenges, with seed germination proving recalcitrant and division impossible. Cuttings offer a possibility but only limited success. Tissue culture emerges as the most promising long-term solution for both quantity and quality of propagation, although requiring significant investment in expertise and resources.
The unique difficulties encountered in propagating this magnificent tree only amplify the sense of accomplishment that comes with success. For the dedicated gardener, the rewards of cultivating a strong and healthy Tree of Heaven, however, it may take more time or effort than the average flowering plant, far outweigh the challenges. Patience, persistence, and a willingness to experiment with different techniques are key to achieving successful propagation. For those seeking a substantial challenge, Androstachys johnsonii offers a thrilling voyage in horticulture.