Flushing out salts

Every time water evaporates from a pot, the minerals in it stay behind. Some come from fertiliser; some come from hard tap water rich in calcium and other minerals. Over months they build up.

You can often see it: a white or yellowish crust on the surface of the mix, around the pot rim or on the outside of a clay pot. The plant may show brown leaf tips, slow growth, dead root tips or wilting even when the mix is damp, because salty mix makes it harder for roots to take up water.

The fix is called leaching. Take the plant to a sink, shower or balcony drain and slowly pour clean water through the mix, at least three times the volume of the pot, letting it run out of the drainage holes completely. University of Maryland Extension suggests doing this every four to six months. If the crust is heavy, repot into fresh mix and scrub or replace the crusted pot.

Leaching only works in pots with drainage holes, which is one more reason the pots lesson insisted on them. Using lower-mineral water, such as collected rainwater, also slows the build-up.