Q. I noticed all my Nandinas, also called heavenly bamboo, are turning bright yellow. Is this a fungal disease problem? I’m worried that whatever this is will spread to all the other plants. A. No, it is not caused by a disease organism. This is severe iron chlorosis and fairly common to heavenly bamboo growing in alkaline and desert soils. Leaf yellowing happens frequently because of a lack in organic matter in the soil, increasing alkalinity or soil pH. I see heavenly bamboo planted with rock mulch and this yellowing frequently becomes a problem in a few years after planting in these situations. Heavenly bamboo and rock mulch and yellowing Start a program of soil enrichment and add a good quality iron product to the soil now as new growth is appearing. If there is rock mulch present, remember this type of mulch is probably adding to the problem. Plants like Nandina do not like rock mulch but grow healthier in a wood mulch environment. Personally, I prefer iron EDDHA chelate as the source of iron to apply to the soil. It is a dry powder and must be watered into the soil accompanied by a good quality fertilizer. Iron does not move from the soil into leaves that are already yellow. Iron applied to the soil only affects new growth and new leaves. The only way to improve the green color of existing yellow foliage is to apply iron fertilizers as a foliar spray. Use any of the iron foliar fertilizers (liquids or powders that are mixed with water to make a liquid) and sprayed on the leaves. Sometimes it can take three or four applications, a week apart, to get them to green up adequately. Some plants green up with a single application. The water used when spraying liquid iron should be distilled water. If using tap water, adjust the pH of the water to 7.0. When making applications to leaves always use a wetting agent such as EZ Wet. You can also improve the new foliage to dark green by pruning them back, close to the ground, and letting them regrow after you apply iron EDDHA, compost, water and a fertilizer.