Citrus trees work hard to produce flowers and then grow the fruit, as well as keeping the foliage green and growing. If short of essential minerals they may abort their fruits or concentrate on growing the fruits at the expense of the leaves. To help them stay healthy, they need regular feeding with a finely-tuned fertiliser which will give them the nutrients they need to perform all these tasks. Light green or yellow leaves on the new growth is a sign of lack of nutrients.