Plant Doctor Archive

Yellow leaves on citrus

I HAVE a Meyer lemon tree that produces quite a lot of fruit. The problem is the leaves turn yellow every year. I have fed with citrus fertiliser, Epsom salts, sheep pellets and even tried lime, but nothing seems to work.

THERE are several factors we need to consider. If the new leaves start off dark green in spring and turn yellow later in summer, it could be mite infestation. The mites are tiny insects that suck sap from the undersides of the leaves. They thrive in hot, dry summer conditions, so you can reduce their effect by spraying the foliage, particularly the undersides, with cold water in the evening or early morning. Or spray with an insecticide such as Conqueror Oil or Mite Killer, making sure to apply it under the leaves and according to the label recommendations.

Citrus sometimes tend to yellow during winter simply because of cold temperatures, but if the leaves don't green up again in spring the problem is probably lack of nutrients. They need lots of fertiliser throughout the growing season and often suffer from nutrient deficiencies, especially lack of nitrogen which causes leaf yellowing, so you need to feed them regularly to keep them growing well and looking green. In spring, and again three months or so later, apply citrus fertiliser at around a handful per square metre to all the soil beneath the tree, and water it in to encourage strong growth.

Lemons sometimes also suffer from trace element deficiencies, but regular applications of citrus fertiliser should supply the necessary elements. Also worth trying is regular summer watering, deep into the soil if necessary, once or twice a week during dry periods along with mulching over the root system to conserve moisture.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.