Bonsai Health and Basic Care Workshop for Curators, Jonas Dupuich, Part 2
By Janet Nelson and George Haas
Photos by George Haas
May 22, 2025
This is a follow-up to Jonas Dupuich providing professional training for volunteers who care for and maintain the bonsai trees in the Bonsai Garden at Lake Merritt collection.
On May 13, 2025, Jonas Dupuich continued to provide professional training to volunteers who are responsible for caring for and maintaining the bonsai trees in the Bonsai Garden at Lake Merritt.
As a follow-up to Bonsai Health and Basic Care Workshop for Curators Part I, Jonas led the discussion on Pests, Diseases and Fertilization. Jonas presented a process to identify a tree’s condition in order to decide what treatment would be appropriate. The process can then be used for other trees as well, rather than merely recommending treatment for an individual tree.
Garden curators are expected to recognize abiotic problems, diseases and pests during their routine observations of the collection trees, and then take steps to resolve the health problems.
Abiotic Problems
Abiotic deficiencies are caused by something that is not a living thing, e.g., water, exposure, temperature, physical damage (hail, sun, wind).
Slides were used to show anemic (pale) leaves suggesting specific deficiencies.
Yellow leaves with green veins suggest an iron deficiency, too wet, bad soil, or poor water quality. The pH can affect nutrient absorption. One can send leaf samples to a private lab for analysis for a fee; one old leaf and one new leaf from the same tree to analyze the progress and plan treatment for that specific plant (not just that species). Some county agriculture departments and universities also do tests, but their results may be less specific.
Brown or “shady” leaf tip pattern indicates nutrient deficiency. Brown leaf margins can indicate extreme nutrient deficiency plus multiple problems, e.g., poor soil. Recommended organic fertilizers include fish emulsion, with or without kelp. Recommended chemical fertilizers include liquid Miracle Gro.
Pine needles that are yellow on the inside at the base with creamy transition to green tips indicate too much water; nitrogen deficiency can be caused by too much water washing it away.
Tip wilt or margin burn on leaves can be caused by insufficient water or by sun and wind.
Pests and Diseases
Pests and diseases have biotic causes.
Jonas went through the list of pests and diseases as described during Part 1.
The ability to identify specific pests and diseases lends itself towards finding solutions to eradicate pests and eliminate or control diseases.
Insecticidal soap is a great all-purpose treatment for virtually all pests. Its use can lead to degradation of the cuticle making it susceptible to burn.
A new product is now available for year-round usage “All Seasons” Bionide Horticultural and Dormant Spray Oil.
Resources
Jonas recommends using Integrated Pest Management (IPM) principles for treatments that are effective and environmentally safe. They can be researched online by searching “IPM” with the name of the condition you want to treat, for example “IPM scale.”
Predatory insects can also be used.
Do-My-Own Pest Control website (https://www.domyown.com) is useful to search by product or insect. It can be expensive. Forest Distributing website (https://www.forestrydistributing.com) may have cheaper prices. The JC Chang newsletter “Pest Talks” is useful. Arbico Organics (https://www.arbico-organics.com) is another resource for IPM. Waypoint Analytical testing lab handles foliage and roots in a single sample for $130.
Fertilizer
Basic Protocol – put a ring of mild fertilizer around every tree (granular or liquid) between January 1 and May 1 when you see signs of new growth. But not on trees where you want to limit leaf size or internode length such as Japanese maples, white pines.
Defer fertilizing deciduous trees until the first flush of new growth has hardened off, then put fertilizer, more on plums, wisteria. Wait at least one month if the tree has been re-potted. Less fertilizer on junipers, Rocky Mountain species; more on pines.
Tour of the BGLM Garden (Observations/Recommendations)
Upon completion of the lecture, Jonas led the group on a tour of the bonsai garden, pointing out various observations and recommendations based on the aforementioned topics.
