Pruning, feeding and treating for disease are all parts of caring for citrus trees in the lead up to the Auckland winter. We’ve planted a lot of citrus trees, usually lemons and mandarins, for clients over the years and always offer guidance to keeping them growing well through the seasons.
Pruning citrus trees
Now that summer growth has slowed, this is a great time to examine your citrus trees, lemon trees, orange trees, mandarin trees etc, and decide if any pruning and trimming is necessary.
Firstly look for evidence of the lemon tree or citrus borer – holes and cavities with sawdusty, web-like extrusions. Because the lemon tree borer is active during summer it’s important to avoid pruning between November – March because the freshly cut ends of branches leaves your trees especially vulnerable to this insect taking hold. At this time of year if you see signs of lemon tree borer, cut out all infected branches and permanently dispose of them, ie don’t add them to your compost. It can also help to make up a solution of Neem Tree Oil and water it into the root area after sprinkling Neem Tree Granules on the soil.
Modern citrus varieties tend to be small and dense, handy for picking fruit but the dense foliage can restrict light and retain moisture which can lead to problems during winter.
Assess the branch structure and prune for light and shape, focusing on damaged, spindly and diseased branches, inward growing branches and branches that overlap or nearly overlap. Cut right back to the base of the branch as trimming halfway will just encourage a flush of growth at that point. Pruning will encourage new growth on healthy branches.
If your trees are hit by frost in winter and spring, don’t be tempted to immediately prune the affected parts as this will just encourage new, vulnerable growth.
Fertilising citrus trees in winter
Citrus trees are big feeders, even at this time of year with our mild Auckland weather, and especially for species like grapefruit and tangelos. Rather than using slow release fertilisers which harm the soil life and worms, make up your own food with seaweed, sheep manure pellets, blood and bone and monthly doses of sulphate of potash for root and flower growth and to add extra flavour and sweetness to the fruit.
Winter problems with citrus fruit
Verrucosis or citrus scab looks unsightly but doesn’t affect the quality and taste of the fruit. If you like to use the zest you can spray with copper twice a month or as needed, but otherwise you can leave it be.
Blossom-end rot causes brown scaly patches at the end of the fruit, dry fruit and early fruit drop. This is simply due to a lack of calcium in the soil and is easily treated – just sprinkle a handful of lime around the dripline and continue a regular feeding regime.
Some citrus leaves become somewhat yellow over winter and this can be due to being grafted to deciduous rootstock such as Trifoliata or Flying Dragon. Being deciduous, they stop taking up nutrients during winter, leaving the foliage of the grafted variety hungry for food and looking yellow or mottled. Lime and gypsum will help with trace element nutrition and you can wait until spring before feeding as usual.
Collar Rot is a fungus present in the soil and it rots the base of the tree trunk just above ground level. First causing the yellowing of leaves and splitting bark, this can eventually kill the tree. Preventative methods include well-drained soil and keeping mulch and grass clippings away from the base of the tree. If infected, cut back diseased wood and spray with an anti-fungus spray.
Winter fruit in young citrus trees
As hard as it can be to have patience, you’ll reap the rewards if you can prevent your tree from fruiting in the first 2-3 years. Rub off new fruit buds or cut off with secateurs if too big already. Waiting until your tree is mature before fruiting will result in a stronger tree and larger fruit.