Citrus tree don't thrive outside in the UK's climate but you can grow them in pots in a conservatory or greenhouse. There are many reasons the tree might be ill, including insect infestation, disease, lack of general care and improper growing conditions. An ailment that affects one type of citrus will not necessarily affect another citrus species. If after inspecting your tree carefully and taking measures to correct the problem it still does not recover, you might need to call a specialist or remove the tree and replace it with a new one.
Remove grass and weeds from around the base of the citrus tree. Excess greenery can harbour insects and take nutrients and water from the tree.
Remove shrubs and shade-casting plants from the area of the citrus tree. Citrus trees need full sun to thrive.
Prune the tree. Remove suckers, found in areas such as under grafting scars and around the base of the tree; they take the water and nutrients from the tree but do not produce fruit.
Water your tree well. Citrus plants need plenty of water, especially in the summer.
Improve the drainage around the citrus tree if the soil is retaining water. Citrus trees need good drainage or they will suffer from root rot and other fungal infections.
Mulch around the base of the tree to keep weeds down, but do not mulch right up against the trunk because this can cause collar rot.
Apply fungicide if you see signs that your tree has a lesion. Lesions can be caused by an injury to the tree and create a place for fungus to enter.
Dig composted cow or horse manure into the base of the tree. The manure will enrich nutrients and provide better drainage for the tree.
Fertilise the tree with fertilisers formulated for citrus trees in late summer and late winter. Water the tree well before and after fertilising to avoid burning the roots.
Treat any disease you find on your citrus tree with the correct treatment. For example, brown rot causes the ripe or ripening fruit to decay and part of the treatment is to remove the affected fruit and prune low-hanging branches.
Inspect your citrus tree and its fruit for damage by insects. Implement the correct treatment for insects on your tree. For example, use the natural predator trichogramma platneri to control the insect amrobia.
Avoid the use of pesticides because they disrupt the natural ecosystem, including natural predators.
When using chemical treatments on your tree, follow the manufacturer's directions carefully.