Most people who know their way around the kitchen know lemon juice can be used to keep foods like apples and avocados from turning brown when their flesh is exposed to oxygen. What may not be known is why the flesh of a lemon turns brown. Rather than exposure to the elements, the browning of the inside of a lemon indicates a mineral deficiency, or possibly the presence of an insect pest.
Quite a few symptoms become apparent in lemons when they do not receive enough minerals. When the flesh of a lemon is brown when the fruit is cut open, it indicates a boron deficiency. The flesh may also be dried out when boron is deficient. The cause is likely from acidic soil in the area where the lemon tree was planted.
Boron Deficiency Solution
The lemon tree can be salvaged if it has a boron deficiency. One tablespoon of borax should be in an equal amount of hot water. Once dissolved, the solution should be mixed into 9 litres of water. Spread this mixture across the soil, starting from the trunk and extending to the farthest reaches of the tree's foliage. Do no use more than this prescribed amount, and do not add to the soil more than once a year.
Should the lemon tree be found not deficient in boron, the source of a lemon's brown, dry flesh may be from the Spined Citrus Bug. These bugs pierce the rind of the lemon and suck out the fruit's contents. Beyond the browned flesh, a tree that was attacked by this pest sheds its young fruit, and mature fruit have dry patches on the rind.
Identification and Control of the Spined Citrus Bug
A young Spined Citrus Bug is either yellow or orange. An adult is green. The bug has projecting horns on either side of its head. Getting rid of these bugs requires hand-picking them off the fruit and trees.