Buying trees
Only buy trees from a reputable source. Look for trees with healthy green growth, no leaf yellowing or leaf drop and that look proportional to the pot they are growing in. Trees that have been in the nursery for a long time can be pot bound which means that root strangling and entwining may have occurred.
A common fallacy is that older bigger trees will grow and fruit better than smaller trees. One-year-old trees can be more successful than older trees that may be pot bound and will need more pruning after planting.
Planting
Much of the success with citrus trees depends on the initial start the young trees receive.
Select a site that doesn’t compete with established trees or lawns, is protected from strong winds and has a sunny aspect. It is preferable to plant trees in spring after the risk of frost has passed. However, trees can be planted from autumn to spring in warmer areas.
Dig a hole 75cm deep by 75cm wide, and apply a mixture of compost, phosphorous (rock phosphate at 1kg per tree, or superphosphate at 500g per tree) and trace elements (100g per tree). Mix this up with some soil in the bottom of the hole and place some soil without fertiliser over the top. In sandy soils add about 5% clay to the improved soil to help with water retention. Plant the young tree on top making sure the roots don’t touch any fertiliser grains and that the bud union (variety and rootstock join) is well above the ground level. If the bud union is covered with soil this can allow diseases such as collar rot to develop in the tree.
Try not to disturb the root ball too much at planting. Firm the soil around the roots, apply a wetting agent and water immediately.
It is advisable to prune the top of larger trees after planting. If the top has many branches cutting back to three well-balanced branches 15 to 20cm long will develop a healthy framework. If the top of the tree is too big for the root ball to support leaf drop and poor development will occur in the year after planting.
Caring for young trees
The trunk of the young tree should be protected from the sun in the first few months after planting. This can be done using commercially available tree guards or by loosely wrapping the trunk with shade cloth or a similar material.
Spread mulch around the tree to cool the soil in summer and reduce moisture loss. Apply sufficient water to keep the soil moist to a depth of 30 to 50cm. During the first growing season apply a commercial, slow release fertiliser, following label instructions for application rates. Frequent applications of small amounts of fertiliser will stimulate growth and bring the tree into bearing sooner. Liquid fertilisers containing trace elements, compost and fish can be applied to the foliage of the trees monthly to boost growth and address trace element deficiencies.
Established trees
A common mistake is to prepare the soil carefully before planting, but fail to adequately supplement the tree in later years. This reduces growth and bearing.
Citrus trees need a lot of nitrogen and potassium, and small amounts of phosphorous and trace elements. In Perth’s sandy soils a suitable fertiliser programme providing all the trees nutrient requirements is essential. Apply 50g of a suitable balanced fertiliser containing nitrogen, phosphorous and potassium to each tree every five weeks in spring (3 to 4 applications). Also apply a commercial citrus fertiliser mix containing trace elements (as recommended on the label) during the growing season. One or two additional trace element sprays in spring and during fruit set will improve fruit quality. Always water trees before applying fertiliser and do not use excessive fertiliser as too much can burn the leaves and cause leaf drop.
Using organic matter like compost or well rotted manure beneath the mulch encourages beneficial organisms and reduces summer soil temperatures.
Remove weeds by hand being careful not disturb the soil around the trees more than necessary. If spraying weeds avoid foliage contact with herbicides such as glyphosate as these can cause severe damage, particularly in young trees.
Watering should aim to wet all the roots of the tree. Citrus are shallow rooted with the main mass of roots located in the top 30 to 40cm of the soil under the tree canopy. As the spread of water is poor in sand the full root perimeter should be watered. Watering from a hose running under the tree soaks quickly into the ground without benefiting the main lateral roots and also washes soluble nutrients away from the roots.
Citrus trees do not need extensive pruning, but shoots developing on the trunk should be removed and the trees should not be allowed to get too big to make it easier to pick fruit and control fruit fly. On older trees, strong shoots from the main head should be shortened or removed to prevent the tree becoming unbalanced.
Old trees will benefit from periodical pruning, involving thinning out limbs where they have become thick and entwined and removing dead wood.