Monday | October 23, 2017
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Garden Guy: Why is my blue ginger turning yellow?

I notice a lot of blue ginger plants in Hawaii have yellowing in the younger leaves. I assume this is from having the wrong pH or from lack of some nutrient. Do you know how to correct the problem? — L.W.M.

There a number of reasons why the leaves of blue ginger, and other plants, would turn yellow.

Here are the reasons:

1. Although it will grow in full sun, it does better in partial shade; it also prefers cooler climates. Consequently, growing in full sun, especially when temperatures rise above 86 degrees, can cause a yellowing of the leaves.

2. Blue ginger also grows best with a soil pH of 6.1-6.5. Soils in Hawaii can certainly drop below that range.

3. A lack of nitrogen will cause a light green to yellow coloration in leaves.

4. Since you mentioned yellowing in the young leaves, I would point out that many times young leaves are lighter in color when they first emerge. If conditions are suitable, as the leaf matures it will darken.

5. And lastly, there are always the unknown factors. These are the miscellaneous maladies such as vog, disease and insect pests as well as herbicide sprays. Note: Blue ginger, Dichorisandra thyrisifolia, is not a true ginger.

Aloha Nick, I read your article “Controlling weeds organically.” I am interested in using powdered citric acid (left over from the failed coqui frog control program) as an herbicide, but I can’t find a formulation (ounces/gallon). The intended use is on grasses and honohono grass. Can You help? — Mahalo, J.S.

I will direct you to an informative website from the University of Purdue Extension: Here, you will find a publication titled, “A Comparison of ‘Natural Products’ for Organic Production.” The article looks at a number of natural, common ingredients such as vinegar, clove oil and citric acid and compares their effectiveness in controlling a number of weeds; dosages are given. From this and other publications, it would seem that a 10 percent solution of citric acid is a good starting point.

I would set up an experiment comparing 5, 10 and 20 percent solutions of citric acid on various garden weeds. Remember it is important to spray the weeds when they are young.

Some commercial products add garlic to a citric acid or vinegar spray for increased efficacy. One product in the article contained 10 percent citric acid and 0.2 percent garlic.

Summerset Products ( sells two organic herbicide. One is AllDown, 8 percent acetic acid (vinegar) and 6 percent citric acid, the other is AllGuard, a 48 percent garlic juice product.

I have a papaya plant that I suspect has the ringspot virus. What can I spray to kill out this disease? I have access to lots of compost and some horse manure, can I put this on the ground to help the trees and maybe kill out the disease? Thanks for your help.

There are no sprays for the papaya ringspot virus, don’t waste your money.

Production will be severely reduced, and the plant eventually dies. In addition, infected plants need to be removed because they are a source of the virus which can be spread to healthy plants by aphids.

The virus is not in the ground so soil treatments would be useless. Compost, manures and other fertilizers are all good but in this case will not control the papaya ringspot virus.

There are a number of publications about this disease on the College of Tropical Agriculture and Human Resources website,



Don’t forget, this Saturday from 9:30 a.m.-12 p.m. is my class on tropical fruit trees at the University of Hawaii at Hilo. Call 974-7664 to register; or visit There is a fee.

Hilo resident Nick Sakovich is a professor emeritus of the University of California. He has worked in the field of agriculture for 30 years. Email your questions to Sakovich at You also can visit his website at


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