Apply or renew mulch over the root system of the citrus tree. One thing that citrus trees really hate is having to fight with grass growing right up against their trunks. Grass is so greedy it will gobble up any nutrients it can get at.
Clear grass away from the base by hand, or carefully spray with Zero. When all the weeds and grass have gone, give the roots a really good drink and then put a 10 centimetre or more thickness of organic mulch (old manure, grass clippings, compost) over the entire root area. Make sure that the mulch is not contacting the trunk (because this will encourage root and collar rots).
Prevent Root and Collar Rot
And speaking of rots, citrus roots rot away very readily when the soil is heavy or clayey, and citrus bark can decay and lift from almost any part of the tree (collar rot). The layer of organic mulch will help to introduce more air into the soil, but the best defence is to spray citrus plants a couple of times a year with Yates Anti Rot. This low toxic fungicide gets right inside the plant and helps it to withstand the fungal diseases that so often attack citrus, especially lemon trees.
Control Insect Pests
Citrus trees are also attractive to a number of insect pests. The most difficult to diagnose is citrus leaf miner, a tiny caterpillar that burrows its way through the leaf tissues and causes new leaves to twist and curl. Sometimes the trails left behind by the caterpillar can be clearly seen inside the leaf. They look a bit like snail trails, which throws some gardeners off the scent. Spraying the trees every 10 days with PestOil during summer and autumn will smother the tiny caterpillars within the leaves and deter the adult moth from laying its eggs. Avoid applying any type of oil on hot days because it could burn the leaves.
Nasty stink bugs (Bronze Orange Bug and spined citrus bug) on non fruit-bearing citrus, can be controlled with Yates Nature’s Way Citrus & Ornamental Spray, or picked off by hand and squashed. These horrible creatures can squirt out a caustic substance when attacked, so be sure to protect yourself by wearing glasses, long sleeves and gloves.