Plant Doctor Archive

Unwelcome inhabitants

CAN you advise me what to do about maggots and their eggs throughout my large potted plants? I discovered them while adding slow release fertiliser and the smell was so bad it almost made me ill. Only the plants I have added compost to seem to be affected so they must be in the compost, contained in a large plastic commercial bin. Will I have to repot all those plants, including dwarf citrus trees? Is my compost no good now?

COMPOST is an ideal additive to mix with garden soil but it's no good as an alternative to potting mix as the decomposition process that starts in the compost heap continues to work in the pot, resulting in all sorts of problems such as you have experienced. Most good potting mixes are made from materials that are very slow to decompose such as granulated pine bark, peat and sand. This provides a good environment for root growth but at the same time a relatively unattractive one for insects and other nasties.

My advice is to repot your plants into a commercial potting mix. There are plenty to choose from and most garden chains have their own range. For dwarf citrus trees choose a mix with slow release fertiliser that lasts at least 8-9 months, rather than the 3-4 month types.

Reproduced with permission from the former Weekend Gardener magazine. The views expressed here are not necessarily those of the RNZIH.