Growing Citrus Trees

It’s almost mandatory to grow a citrus in the Australian backyard, especially a lemon.  No citrus fruit purchased at a supermarket has the same flavour as one picked, peeled and eaten in the backyard and with such diversity in size and varieties there is a citrus tree to suit any garden, backyard or balcony.

Citrus have many more benefits than just the delicious, brightly coloured fruit.  They produce the most glorious perfumed flowers and are covered with glossy, green leaves that make these terrific feature trees in the landscape or eye-catching informal hedges. 

Citrus are best where the days are long and sunny and do not thrive in frost prone areas.  They are quite demanding when it comes to soil quality and are very hungry and thirsty.  Be sure to regularly add slow release fertiliser to those in pots and don’t allow them to dry out.

All citrus grow very well in large tubs but in recent years new dwarf varieties that still produce masses of full sized fruit make growing citrus on patios and balconies very easy indeed.  Choose as large a container as possible, use premium potting mix and ensure that it is in a bright, sunny position.

PLANTING
Citrus are best planted in an open, sunny aspect where they will not have to compete with established trees and lawns and are protected from strong winds. 

When planting, dig as large a hole as possible.  Mix a combination of compost and dynamic lifter with the soil in the bottom of the hole.  On top of this put a layer of soil without fertiliser which will help stop the young roots from burning.

Buying younger trees is often more successful than older trees as their roots establish more quickly and they need less pruning to form a balanced canopy.

Without disturbing the root ball on the new tree, place it in the hole making sure the roots don’t touch the fertiliser and that the graft union on the stem is well above ground level.  Firm the soil around the roots and water immediately with a seaweed solution.

If the tree is very large, it is a good idea to prune the top after planting to prevent leaf drop and poor development.  If the top has many branches, cutting back to three main branches about 15 to 20cm long will help to develop a strong framework.  Young citrus need some protection from the sun in the first few months after planting.  Protect their trunks with tree guards or by loosely wrapping with shade cloth and mulch well to prevent moisture loss.

WATERING AND FERTILISING
Citrus have shallow feeder roots which concentrate under the trees canopy so keep the soil moist to a depth of at least 30 to 40cm.  Citrus are very heavy feeders because they have rapid growth and bear enormous amounts of fruit.  Commercial citrus fertilisers that contain trace elements should be applied during the growing season and then again in spring and when the fruit is setting.

If spraying weeds with glyphosate be very careful as even the slightest overspray can cause severe damage to citrus trees.

Adding compost or manure to the base of citrus trees regularly will help to reduce soil temperatures, reduce weeds and encourage earth worms.  Hand weed around the trees being careful not to disturb the soil.

PRUNING
Citrus do not require annual pruning except to prevent the tree from becoming unbalanced.  If three main branches are developed whilst the tree is still young, an open canopy will form and the tree will only need to be kept to a manageable height.  On older trees, strong shoots that grow from the main branch should be shortened or removed so they don’t take over and dead wood and tangled limbs can be removed.  Remove any shoots that develop on the trunk, especially those below the graft union.

PESTS AND DISEASES
Mediterranean fruit flies lay their eggs in the ripening fruit and the larvae feed on the flesh rendering it inedible.  Mandarins are highly susceptible and lemons and grapefruit are hardly affected.   Infested fruit must be destroyed to prevent the larvae from developing.  The fly is attracted to the colour yellow so yellow sticky paper and fly traps hanging amongst the trees are very effective at trapping them.

Whitefly will suck sap from the tree as well and cause a sooty mould on the fruit which turns to sugary syrup.  They swarm the trees and are obvious when the branches are disturbed.  White oil will help control these pests but yellow sticky paper will also trap them and help control their numbers.  Other pesticides are available that will assist.

Scale is not uncommon on the leaves and trunks of citrus.  If there are just a few, they can be scraped off with a finger nail but where there are too many, spraying with White Oil or Pest Oil will suffocate the little insects that sit under the shell.  Do not apply in the heat of the day however as the oil content will burn the leaves.

Aphid may appear on new growth and buds but are easily dealt with by using Confidor or other suitable insect sprays. With aphid, and in fact mealy bug and scale, ants are often present as they “farm” these insects to feed on the sugary nectar that they excrete.  It is important to treat the ants as well as the insects otherwise the problem will not be resolved.

Citrus leafminer moths are rarely seen but their caterpillars leave a silvery trail through the centre of soft new leaves leaving them twisted and distorted.  To reduce the population prune new leaves when leafminer numbers are highest and fertilise in winter to promote strong spring growth.  Pest Oil is effective at controlling leafminers but don’t apply in the heat of the day.

OTHER DISORDERS

• Collar Rot girdles the trees trunk. Do not allow mulch to pile up against the stem or the soil to build up above the graft union.  Anti-rot products will assist where damage has already occurred and good air flow is essential.
• Root Rot attacks and kills the roots of trees.  Anti-rot products are safe and available to treat the tree.
• Fruit Rot is caused by blue and green moulds on fruit hanging within the tree canopy.  Provide more light, check for insects and destroy fruit immediately.
• Young fruit dropping from the tree or sunburn on the fruit is probably caused from excessive heat and harsh sun.  Don’t allow the soil around the tree to dry out and consider covering the tree with shadecloth until the weather cools.

JOBS THROUGH THE SEASONS

SUMMER December – February

• Prune the trees once all the fruit is picked.
• Water well throughout summer.
• Thin the fruit if the tree is too heavily loaded.
• Fertilise a little.

AUTUMN March – May

• Some mandarin are ready for picking.
• Plant new trees whilst soil is still warm.
• Fruit changes from green to orange.
• Put up fresh yellow sticky traps.
• Continue watering & lightly fertilising.

WINTER June – August

• Most varieties are picked throughout winter.
• Control weeds so they don’t steal nutrients.
• Fertilise a little.

SPRING September – November

• Fertilise very well in spring.
• Prune in late November through December.
• Fruit begins to set in early spring.
• Control weeds and insects.