Q.What causes an orange tree to turn sour, with a thick bumpy skin? Can it be fixed?
(Linda Hutcheson, 5 December 2008)
A.Thanks for your question. Sweet oranges can be difficult to grow in this country – they’re native to Mediterranean climates, where they grow on warm southern slopes in Italy and Spain. Orange trees are susceptible to frost, so they must be brought indoors before any risk of frost (late October in the South; check online for last frost dates in your region). Summer fertiliser helps to improve the fruiting quality. Once fruits form, they can take up to a year to be ready for eating; the orange tree has a very long ripening period, so it could be that your fruits just need a little longer on the tree.
It could simply be that your orange tree has not had enough sunshine for its fruits to fully ripen this year. In 2008 many crops suffered from the lack of long, sunny days at the end of summer: squash and corn, two other warm-climate crops, did not fully ripen for many British growers (even the professionals!). Orange trees don’t fare well outdoors in Britain – except for a few notable exceptions on the far South coast, where conditions are more Mediterranean. Orange trees like a warm, humid atmosphere to produce the best fruit, and this is not typical of our British summers. As a result it’s best to bring the plant in to a conservatory or warm window as autumn arrives, to give it plenty of sunshine without chill. Orange trees like a minimum temperature of 13 degrees C during the winter, so pick a good spot for the best chance of survival.
You should also water and feed your orange tree occasionally in the summer (once a week with a citrus fertiliser) but look out for overwatering – leaves will droop or turn yellow.
If you’d like to try again with a reliably sweet orange, the RHS recommends Valencia (citrus sinensis) for eating (follow the care tips above). There are many varieties of bitter orange too – don’t discard the fruit, though – they’ll make great marmalade!
For lots more information about growing oranges, lemons and other fruit, check out the navigation menu on the left hand side of this page.