Hardening, aphids & quackgrass

Q: What on earth does it mean to "harden" a plant?

A: It is gardeners' slang for helping an indoor plant to adapt itself to outdoor weather. The same techniques are used for plants grown in a greenhouse or bought at a nursery.

The leaf surfaces of plants are delicate if they have always been warm, have never felt wind, have never seen bright sun. Amazingly, plants can toughen their leaves to adjust to weather, but they cannot do so instantly. It is as if the plant grows itself a jacket, and the process takes about a week.

If a house or greenhouse plant is put outdoors, it probably will survive...