Lemongrass

Blade tips turn brown and dry, and the browning creeps further down each week

Drying out. This is a monsoon grass that expects heat and water together, and it will not shrug off a dry pot the way a Mediterranean herb does.

Fix: Move it into a deeper pot with a moisture-retentive mix and water before the surface dries. Trim the brown tips off with scissors if the look bothers you. The plant is fine below them.

Stops growing over winter and the whole clump pales

Growth stalls below 50°F and the plant part-shuts down until the warmth comes back.

Fix: Move it off the window into the warmest room, cut the watering back while it is idle, and hold the feed until spring. If it looks rough, cut the clump down to a few inches; it comes back from the base.

Supermarket stalk sits in water making leaves and no roots

The base was trimmed too far back, or the water has gone stale. Roots come out of the swollen basal plate. A stalk cut above it has nothing to root from.

Fix: Pick stalks with the firm bulbous base intact and a bit of root scar showing. Stand them in an inch of water somewhere warm and bright and change the water daily. Roots usually appear within one to three weeks.