Got a houseplant query? Our expert is here to answer them. This week, how to revive an ailing dragon tree

What’s the problem – is it rust?
My 10-year-old dragon tree has been happily growing in a bright attic room, but recently the leaves have developed brown splotches.

Diagnosis
It’s unlikely to be rust (a fungal infection). Dragon trees (Dracaena marginata) are not particularly prone to rust infections – the splotches are more likely caused by under-watering, tap water or dry air from being too close to a heat source. Dracaenas are very sensitive to salts, minerals, and chemicals, such as fluoride and chloride, which can lead to leaf discoloration.