Last Christmas saw garden centres being flooded with little citrus trees: lemon, orange, calamondin, kumquat, limequat, mandarin, to name a few. Chances are that if you received one, it may be looking a little peaky. One of the causes is that many were sold potted up in light-weight, short-lived compost and now need to be repotted into a heavier mixture.
Most citrus plants require a slightly acid medium, so use about one part ericaceous compost, two parts John Innes number 3 compost and one part sand or grit. Be sure to add a generous layer of crocks (broken pot-pieces) or other drainage material at the bottom of the pot. A sprinkling of pelleted poultry manure in the lower layer of compost will help feed the plant in the months to come. If you have a sheltered position in the garden, put your citrus plant out for the summer, after all, risk of frost is past.