Tropical Gardening Helpline: Ample reasons for yellow bonsai leaves

  • Yellowing leaves can be indicative of either water or fertilizer stress. (Schefflera bonsai with chlorosis from houzz.com)
  • Dwarf schefflera trees make excellent bonsai plants but need the correct balance of water and nutrition to stay healthy. (Schefflera bonsai from interiorplants.ca)

Danni asks: My schefflera bonsai doesn’t look good. The leaves are yellowing and some are dropping off. What’s wrong and what can I do about it?

Tropical Gardener Answer: Bonsai plants can be very sensitive. Leaf yellowing, or chlorosis, can be caused by several factors. See which one or ones likely apply in your case and proceed with the recommended remedy.

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Most schefflera bonsai plants are created using the dwarf umbrella tree, Schefflera arboricola. This evergreen shrub with deep green palmate leaves makes an attractive landscape specimen or house plant. It also adapts well to bonsai containers where it will stay small since its roots are constrained.

The leaf yellowing you report could be caused by the plant’s location or by your watering or fertilizing practices.

A schefflera bonsai should do well either inside or outside. It will do best out of direct sunlight and can tolerate fairly low light conditions. Too much sun can burn the leaves.

Though your bonsai is somewhat drought tolerant, it will do best with regular watering and occasional misting. It is important that the pot it is in drains well so the soil can dry out a bit between waterings. Leaf yellowing can be caused by overly dry or overly wet conditions in the root zone. Get on a regular watering and misting schedule and see if that helps.

Another issue that can cause chlorosis is nutrient deficiencies. Plants, like people, need food. Small bonsai pots with small amounts of soil can lose nutrition quickly. Finding the right balance of nutrients for your plant is essential to its health. Over-fertilizing can burn the roots and under-fertilizing can starve them; either can cause leaves to yellow and drop.

Feed your plant with a slow release or organic fertilizer with a balance of nitrogen, phosphorus and potassium (N-P-K). Minor nutrients like calcium and zinc are also important. If the yellowing is on the older leaves, it is probably a nitrogen deficiency. If younger leaves are yellowing it may be a zinc or micronutrient deficiency. You can try using a chelated zinc formula that can be sprayed on the leaves for foliar feeding.

Having the acid-alkaline balance in the soil around pH 6.5, slightly acid, will help your plant’s ability to absorb and utilize the nutrients you apply. You can get test kits at the hardware store but for really accurate results you might want to get a soil test and maybe a tissue sample done. UH CTAHR can do these for you. Check out their publications on these at www.ctahr.hawaii.edu/oc/freepubs/pdf/SCM-9.pdf then call 322-4893 to find out when and where to drop off your samples.

Most bonsai plants can use fresh soil every two years or so. Be sure to remove them carefully from their pots and replace the soil with one that drains well. During repotting is a good time to apply a bit of fertilizer.

As with all plants, healthy soil supports healthy plants. Balancing the moisture and nutrient levels in your soil should address the leaf chlorosis. If not, you may want to get some tests done to give you precise nutritional and pH information on your soil and reveal what nutrients are actually being absorbed by your plant.

Hopefully, you can get your plant healthy soon by following one or more of these recommendations.

Diana Duff is a plant adviser, educator and consultant living in a dryland forest north of Kailua-Kona.

Gardening Events

Saturday: “Work Day at Amy Greenwell Garden” from 9 a.m. to 12:30 p.m. Meet at the Garden Visitor Center across from the Manago Hotel in Captain Cook. Volunteers will be able to help with garden maintenance and are invited to bring a brown bag lunch. Water and snacks provided. Call Peter at 323-3318 for more information.

Farmer Direct Markets

Wednesday: “Hooulu Farmers Market” 9 a.m. to 2 p.m. at Sheraton Kona Resort &Spa at Keauhou Bay

Saturday: “Keauhou Farmers Market” 8 a.m. to noon at Keauhou Shopping Center

“Kamuela Farmer’s Market” from 7 a.m. to noon at Pukalani Stables

“Waimea Town Market” from 7:30 a.m. to noon at the Parker School in central Waimea

“Waimea Homestead Farmers Market” from 7 a.m. to noon at the Waimea Middle and Elementary School Playground

Sunday: “Pure Kona Green Market” 9 a.m. to 2 p.m. at Amy Greenwell Garden in Captain Cook

“Hamakua Harvest” 9 a.m. to 2 p.m. at Highway 19 and Mamane Street in Honokaa

Plant Advice Lines

Anytime: konamg@ctahr.hawaii.edu

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Tuesdays and Thursdays: 9 a.m. to noon at UH-CES in Kainaliu – 322-4893

Mondays and Fridays: 9 a.m. to noon at UH CES at Komohana in Hilo 981-5199 or himga@hawaii.edu