In case you hadn’t already noticed the multitude of orange globes hanging from backyard trees all over the Downs, citrus season has arrived and it’s a beauty. I’m getting lots of reports from home growers that their trees are bearing heavily this year. Mandarins in particular are enjoying a bumper season. A couple of gardeners have even complained that their trees have split, unable to cope with the fruit load. What a mixed blessing – sheer abundance, but a tree ripped asunder.
This seems to be an ongoing theme with citrus. When the trees hit their straps they are incredibly generous bearers, but there’s a flip side, in the form of all kinds of vulnerabilities to pests, diseases and mineral deficiencies. Every garden writer will testify that the most common gardening problem they are asked about usually relates to a citrus tree, but the solution to many problems is actually very straightforward.
Citrus trees are greedy. They lap up any and all nutrients available to them, and positively sulk if denied plant food. So feed them. It’s the best advice I can offer. Get lots of rotted manure and compost into the soil prior to planting, or do the old fashioned trick of planting on top of an animal carcass, then keep the trees nourished by regularly applying both solid and liquid fertiliser.
The healthiest citrus tree in my garden is a Meyer lemon. It’s planted on top of a deceased rooster, and has only ever shown signs of mineral deficiency in the aftermath of last year’s floods, which I’m assuming would have leached nutrients from the soil. For the six months or so following the flood, I fertilised every few weeks with a mix of liquid fish emulsion and seaweed extract, always applying it over the leaves as a foliar feed. This was supplemented by pelletised chicken manure applied at ground level once per season. It’s fair to say that the tree hasn’t looked back.
In fact it’s really hard to over-feed citrus trees. Some of you might have heard the old saying “ask the gentlemen of the house to say goodnight to the lemon tree”. Not many plants can cope with undiluted urine, but when “applied” in moderate amounts, lemon trees in particular (the hungriest of all citrus trees) lap up the nutrient boost. Invest some love in your trees and the soil they are being grown in and they will pay handsome dividends.
Frost is a much trickier proposition. In the coldest parts of the Downs, citrus trees will get burnt in exposed positions and any fruit hanging on the tree at the time of a heavy frost will be badly affected. Down in Stanthorpe, growers have devised all kinds of clever methods for creating sheltered micro-climates, and many older properties will have a lemon tree growing against a shed wall or similar heat sink as a buffer against bitter nights. Even so, a proper killing frost, when temperatures plummet to minus 6 or lower, will damage the least frost hardy members of the citrus tribe, and may even kill some trees outright.
It pays to choose the right trees for your climate. The most cold hardy citrus of the lot are the kumquat and closely related calamondin. Most produce bitter fruit but the cultivar ‘Nagami’ is sweet enough too be eaten skin and all. Next in terms of cold hardiness is the ‘Satsuma’ mandarin, followed by the ‘Meyer’ lemon, actually a cross between an orange and true bitter lemon, and the ‘Wheeny’ grapefruit. Tangelos are reasonably cold tolerant and bitter oranges (such as chinotto) tolerate the cold better than sweet oranges. Anything grown on ‘Trifoliata’ rootstock will gain an extra few degrees of hardiness. The least cold hardy citrus varieties are true subtropical trees such as limes and pommelos,
An exception is the native Australian desert lime, Citrus glauca. This small, shrubby tree is indigenous to western Queensland and thrives in the semi-arid parts of the Downs and Maranoa. Roma couple Jock and Mina Douglas are growing desert limes commercially with great success, finding them to be both very cold hardy and tolerant of scorching heat in summer.
I’m yet to try a desert lime at my place, but I do have a crop ripening on each of my five trees. Being a marmalade lover, my aim is to be able to make a decent jam from my own fruit. Each year the frost gets the better of me, but I still hold out hope.
First published in the Toowoomba Chronicle 26th May 2012. Photo by Justin, Fergus picking oranges.