Tropical Gardening Helpline: 02-19-17


Rick asks: Can I use wood chips from an ironwood tree as mulch for the base of a macadamia nut tree or would the chips be too acidic?


Rick asks: Can I use wood chips from an ironwood tree as mulch for the base of a macadamia nut tree or would the chips be too acidic?

Can I have some macadamia leaves analyzed to determine the correct fertilizer to use on the trees or do you suggest using a balanced fertilizer like 16-16-16?

Tropical Gardener answer: If you read the helpline column last Sunday, you know that ironwood trees needles/leaves are allelopathic. To determine the potential for growth suppression in ironwood chips, you might want to run the test I suggested using water from soaked chips to determine its effect on seedlings. You’ll probably find that chips made from ironwood would be best used in pathways or places that you do not want to encourage weeds or other growth. Use chips from other species (but maybe not Christmas berry) at the base of your macadamia nut tree.

It is a good idea to do a leaf analysis to decide what fertilizer to buy. Information on collecting leaf samples for tissue analysis can be found at Fill out the form at the end of the publication and call the UH-CTAHR Cooperative Extension Service office in Kainaliu (322-4892) to find out when to drop off your sample.

This is a good time to collect leaf samples as the tree produces new leaves. You’ll get the best results if the tree is getting adequate water during these dry times. Choose three or four branches where the bud at the tip of the branch is just opening and beginning to grow. The buds will have three small pale green leaves and look like a claw. Pick healthy leaves from the second whorl of leaves below the bud. You’ll need about 15 leaves per sample submitted. Place the leaves in a plastic bag; label it with your name and the date.

You can find the preferred ranges for plant tissue nutrient levels for macadamia nut trees at Once you get your test results be sure to get fertilizer that contains all of the nutrients your tree needs.

Macadamias grow rather slowly and don’t need large quantities of fertilizer. Apply nutrients based on your tissue sample results about every six months. Do not overfertilize as too much nitrogen can cause chlorosis in mac nuts. Get another analysis again in two or three years to stay current on your tree’s needs. Meanwhile, apply mulch to retain moisture and promote healthy soil. Micronutrient deficiencies are common in some areas, and can usually be corrected with chelated sprays, especially if you only have a few small trees.

Email plant questions to for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.

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

Gardening Events

Monday: “Hawaii Tropical Fruit Growers Monthly Meeting,” 7 to 9 p.m. at West Hawaii Tropical Fruit Growers office 81-6393 Mamalahoa Highway in Kealakekua. Jessica Schmelz will discuss the latest funding opportunities from the USDA Natural Resources Conservation Service. For more information contact Brian Lievens President West Hawaii Chapter at 895-8753 or

Thursday: “CBB 101 Workshop for New Coffee Farmers,” 5:30 to 7:30 p.m. at the UH Cooperative Extension Service Conference Room in Kainaliu at 79-7381 Mamalahoa Highway. Learn how to effectively manage CBB. Beauveria subsidy program coordinators will talk about their programs. Registration is required. RSVP online at or by contacting Gina at 322-4892 at least two days before the workshop.

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

Farmer Direct Markets

Wednesday: “Sunset Farmers Market,” 2 p.m. to sunset at the north makai corner of the Kmart parking lot

Wednesday and Friday: “Hooulu Farmers Market,” 9 a.m. to 2 p.m. at Sheraton Kona Resort and Spa

Friday: “Pure Kona Market,” 9 a.m. to 5 p.m. at Amy Greenwell Garden in Captain Cook

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

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

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

Tuesday through Saturday: “U-Pick greens and produce,” 10 a.m. to 4 p.m. Tropical Edibles Nursery, Captain Cook.

Plant Advice Lines



Tuesdays and Thursdays: 9 a.m. to noon at UH-CES in Kainaliu, 322-4892

Mondays, Tuesdays and Fridays: 9 a.m. to noon at UH CES at Komohana in Hilo, 981-5199 or

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