Growing Citrus: Zest For Life


Eaten fresh, preserved or juiced, backyard citrus is a great addition to your garden.

Citrus is a mainstay of Australian yards. From the ubiquitous lemon tree in the corner through to a kumquat in a pot on the balcony, citrus has so much to offer home gardeners if cared for correctly.

When they’re healthy and productive, backyard citrus is a great addition to any size home garden. As well as providing nutritious food during winter, citrus offers many advantages to a permaculture garden. Hardy, compact and evergreen, citrus can perform tasks like windbreaks and shelter, and dwarfing varieties means they can be happy in a pot which can be moved to suit your needs.

Citrus is a hungry crop and requires regular maintenance to ensure high yields and pest deterrence, but a well-maintained example of a variety chosen to specifically meet your needs will bring many benefits.

Varieties

Lemons are the most common and often the most vigorous citrus trees found in Australian gardens. They’re available in several tried-and-true varieties; there’s Lisbon, which has both a winter and a summer fruiting, there’s Eureka, which fruits year round and Meyer, a mandarin cross which also fruits year round and is the most cold-tolerant lemon variety. An honorary mention goes to Lemonade, another mandarin/orange cross, which resembles a lemon in both appearance and taste but is not nearly as sour and so can be eaten like an orange when it fruits in winter.

Oranges fruit better in warmer climates, with the ripening process taking much longer in the southern regions of Australia. Early varieties ripen at the end of summer, but oranges generally ripen in late autumn into winter, and some will hold fruit into spring. Popular varieties include Washington navel, seedless Valencia and blood orange.

The most common variety of lime is the Tahitian, which fruits from autumn to spring. Makrut limes (also referred to as kaffir limes – a term Pip prefers not to use due to its racist origins) are grown for their aromatic leaf and skin zest. Australian native finger limes are becoming increasingly popular and, due to their pulp having a caviarlike appearance, are often used in fine dining. Ranging in colour from pink through to green, finger limes ripen in winter through spring.

Perhaps the most underrated citrus for urban gardens, however, is the mandarin. Common varieties include Imperial, which fruits in late autumn into winter, and Emperor, which fruits mid-winter. Robby Engall seedless, which is a satsuma variety, is popular and fruits early in autumn. Some old-fashioned varieties which fruit midwinter are Clementine, which produces a small and sweet fruit, and Ellendale, which is an Australian variety dating back to the late 1800s.

The kumquats commonly grown in Australia are actually calamondins, which is a kumquat/tangerine cross. True kumquat varieties from Asia include Marumi and Nagami and their fruiting peaks in autumn and winter. They have sour centres with sweet skins and therefore should be eaten whole instead of peeled. Of all citrus varieties, kumquats are the most cold hardy, tolerating temperatures well below zero degrees.

The Australian native finger lime grows on a thorny understory shrub

Pests And Diseases

Citrus gall wasp has become the most common and invasive pest of backyard citrus. The damage is done when wasps lay eggs in the soft shoots before larvae develops in the stem creating visible swellings, or galls, from which wasps emerge around the end of spring. Pruning out galls or slicing them to expose and kill the larvae – a vegetable peeler works well – should be carried out before October. A preventative control method is to cover the tree with a film of diluted kaolin clay. This stops the wasps being able to lay eggs in the new shoots. It’s safe for pollinators and can be used up until the day of harvest. Kaolin clay is also effective in controlling leaf miner damage caused a small black fly whose larvae travel and feed under the surface of the leaf.

Another common problem is sooty mould. Often found when ants are farming aphids or scale on citrus trees, the honeydew produced by the sap-sucking insects creates the ideal conditions for sooty mould to establish. Sometimes if left, nature will rebalance itself – ladybirds love to eat aphids, for example – but if not, scale and aphids are easily controlled by mixing two parts sunflower oil with one part dishwashing detergent. Once mixed, dilute one tablespoon into one litre of water and spray onto the affected area.

Fungal diseases are more prevalent in humid regions and sodium bicarbonate is a non-toxic anti-fungal agent worth trying. While some regard copper sprays as organic, it’s a heavy metal and long-term exposure can be harmful to both humans and the environment.

Collar rot is common when the tree has been buried too deep or mulched around too heavily, effectively ringbarking the tree. Planting a tree too deep can also result in conditions which are too wet for many citrus trees which can cause destructive diseases such as phytophthora root-rot.

Swelling of citrus branches indicates gall wasp, which is treated by slicing open and exposing the larvae.

Nutrient Deficiencies

Citrus trees require regular feeding and, if neglected, are prone to disorders. Often mineral deficiencies manifest due to temperature changes, for example when warm-climate citrus like oranges are grown in a cooler climate.

Citrus needs more nitrogen than any other nutrient and a deficiency is visible through pale green or yellowing of the leaves. New leaves will be small and older leaves will drop off causing the canopy to become thin. As a result, tree growth will be retarded and cropping suffers through poor fruit set and smaller fruit.

Other common deficiencies are potassium, where a diffused bronze-yellow colour is commonly seen in the spring; magnesium, which results in a distinct yellow pattern in the older leaves, where yellowing begins near the edge and towards the apex resulting in green around veins but yellow leaf margins. Iron deficiency is more common in cooler climates or where soil is too alkaline (high pH) or too wet and thus lacking available oxygen. It creates a distinct pattern in the leaf caused by a loss of chlorophyll where only the main veins stay green and the rest of the leaf turns yellow. Iron is not mobile in the plant, so young leaves are affected while the older leaves may remain green. Iron deficiency can manifest in the winter only to clear up when things become warmer.

What And When To Feed

Citrus plants require regular feeding and will be grateful for food your backyard can supply, like poultry manure, coffee grounds, compost and comfrey tea. Citrus prefers a soil pH of between 6.0–7.0, so use high-acidic coffee grounds sparingly and ensure poultry manure is well composted before adding in large quantities. Comfrey tea is rich in potassium and calcium which can be applied as both a foliar and root fertiliser.

Urea is high in nitrogen which is why many gardeners will wee on their citrus trees, but be careful if they are in a pot because excess nitrogen lowers fruit quality and causes excess growth at the cost of fruit production. The best time to feed is spring and autumn.

Photo by Robyn Rosenfeldt

Pruning Citrus

There are several reasons why you may want to prune a citrus tree; to determine the shape of the tree; to improve the tree’s vigour; to increase the amount of the fruit; or to remove damage or signs of pests and disease.

Timing depends on the circumstances, but generally, light pruning in the late spring is best as maintenance. Hard pruning can be carried out in the late winter if the desire is to encourage new growth to renew the tree (after a gall-wasp cleanse, for example). Be aware that pruning too hard before a period of hot sun can burn branches and invite fungal pathogens and introduce decay.

To prune for a higher yield, always leave enough one-year-old branches, shoots and leaves, while thinning to make way for new shoots for the following year.

Citrus in permaculture

How To Integrate Citrus Into Your System

A common design choice in a permaculture system is to place citrus trees to the south of other deciduous trees, as their evergreen nature does not then shade out other trees in the winter when the sun is low in the sky. Citrus trees generally benefit from the most amount of sun possible, in order for fruit to ripen, and so can handle north- or even west-facing fence lines where other plants cannot.

Citrus trees will benefit from the extra fertiliser provided by chook manure when planted in a chook run, though roots will need to be protected from their scratching. Chickens will also benefit from the shelter provided by an evergreen tree, though planting density should be taken into account to ensure chooks receive adequate winter sunlight.

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