Citrus Trees

COMPOST:  Citrus trees need a slightly acid environment the pH should be between 6 and 6.5 (Lemons slightly lower pH than Oranges) so use a peat-based compost with an additive to keep the compost open, such as horticultural grit, which will give the pot more weight and help prevent it blowing over if it is stood on a windy terrace, or perlite to keep the pot light for easier moving and to keep the roots warm in winter. If you use Sulphate of Ammonia to reduce the pH, be very careful not to overdose, as this will harm the tree, better to leave the peat as it is. Also avoid using composts containing lime which will raise the pH.

FEEDING:  Citrus trees require an intensive-feeding programme continued throughout the year. They need a high nitrogen feed during summer to boost bushiness and growth and to help prevent fruit drop and premature ripening of immature fruits. In the winter they require a balanced formula for natural sustained winter activity, including fruit ripening and to help prevent leaf fall. Trace elements are essential especially iron, magnesium and zinc and will help prevent leaf discolouration.

TEMPERATURE:  Citrus trees prefer cool, not hot conditions and plenty of fresh air and early morning dew. Keep outside as much as possible only bringing it in just prior to the first frost. When inside under glass keep well ventilated, unless this exposes the tree to very cold droughts. A temperature of about 50f would be ideal. Frost will damage tender winter growth and blossom; severe frost will damage winter fruit and may kill the tree. Sudden and extreme changes of temperature may result in loss of leaves, but this is not necessarily fatal to the tree.

HUMIDITY:  Citrus trees like to have water on their leaves, this keeps them cool, keeps them clean and helps keep them free from pest attack, so spray or mist the trees during the summer when outside (you can use the garden hose) and especially during the winter when conservatories can still be hot and dry or if kept in a centrally heated room. This will also encourage fruit setting when in blossom.

WATERING:  Water at least once a week, more frequently during the summer especially if hot and dry. It may be necessary to stand the pots in a tray of gravel in extremely hot conditions.

PRUNING:  The trees can be pruned to the desired shape and size at any time, but preferably immediately after fruiting. There are no special instructions, but the tree will produce a branch from each leaf node so take this into account when cutting back in order to produce a good shape. The fruit is produced on old and new wood and even a quite mature, bare branch or trunk can sprout new growth.

POLLINATION AND FRUITING:  Trees grown from pips will not fruit unless they are original varieties, all sweet juicy fruits are hybrids and are propagated by grafting. Citrus trees are self-pollinating and do not require a second tree for pollination. Citrus fruits are generally harvested between October and March. It is the lowering of seasonal temperatures that ripens the fruit, not the hot sun. Blossom is produced during the winter or early spring, but some citrus trees may produce blossom more than once in the year.

PROBLEMS:

PESTS: Pests will attack the tree in hot dry conditions especially in the winter. Keep the trees cool, well ventilated and misted to help prevent attack. RED SPIDER will produce stickiness on the leaves and the leaf colour will become slightly mottled with a lack of lustre. Reddish-brown dust specks or cobwebs may be seen and black mould will develop on the stickiness. SCALE INSECTS cause curling of the leaves along the spine and they appear as dark waxy specks on the leaves mainly along the spine on the underside of the leaf but also on branches. They also produce stickiness on the leaves.APHIDS will attack new tender shoots and cause total distortion of the leaves and blossom.

TREATMENT: A good wash down with a very soapy solution taking care to gently remove all traces of the pests as you spray should be all that is necessary. Double strength will be needed to treat scale. Soapy solution should have the effect of blocking the breathing tubes of the pests as well as helping to dislodge them. Cover the compost before you start, to prevent pest migrating back to the tree for a second attack.

LEAF FALL: In winter the most common cause is under feeding, as the trees require less water, also frost attack. In summer the main cause is drying or scorching of the roots as the sun beats down on the pot which has stood on a hot patio. Place the pot into a secondary pot containing peat or stones at the base and keep moist. Poor feeding can also cause leaf fall. Water the tree well and improve the feeding programme.

The keys to success

• Citrus trees require full sun, neutral or slightly acidic soil. Water with rain water if your tap water is alkaline.

• Hardiness varies between varieties, so check the cold tolerance of your variety. Trees grafted on to P. trifoliata rootstock have increased cold tolerance.

• In the growing season (late March-October) they need high-nitrogen fertiliser.

• Citrus benefit from high humidity but falter in waterlogged soil, so stand pot-grown plants on gravel in trays of water.

• Prune only to remove dead branches and shoots growing from below the graft level, or to keep the plant at a desired size.

• The scourge of citrus trees is sap-sucking scale insects and mealy bugs. Watch out for a sticky black coating on leaves and use a cotton bud dipped in methylated spirits to get rid of outbreaks.

• Pests can also be controlled with sprays based on plant oils or soft soap, or biological controls.

Citrus are self-fertile, so a single plant will produce fruit.

Plants 1m (ft) tall should bear no more than 20 fruits and may need thinning thinning. Kumquats do not need thinning.

Once fully grown the fruit develops a rich skin colour, and is ready to pick but can also be 'stored' on the tree.