The best time of year to harvest is July, before they get too tough, but when they have a nice length of growth on them, though if you keep cutting them back regularly and using them fresh, you can preserve the new young shoots at any time of summer and autumn. Herbs just before flowering contain the highest concentration of volatile oils and therefore have the strongest flavour.
The conventional method of laying in a store for winter is to harvest bunches of leaves and stems, hang them up in a warmish, dry place until they are brittle, then the leaves can be crumbled from the stalks, rubbed fine and stored in the dark in screw-topped jars. Bay leaves are stored whole.
An altogether fresher taste can be obtained by freezing the herbs green when they are still young and tender. When you need some for cooking they will crumble easily if you do it while they are still frozen solid. Of course, evergreen ones can be picked off the bush at any time when required.
Plagues and pestilences
The troubles that affect shrubs, annuals and perennials (see pages 168-73, 182 and 215-16) can also afflict herbs. Earwigs and caterpillars can defoliate a sage bush if not dealt with quickly. Mint is particularly susceptible to rust. Occasionally parsley can have its roots eaten away by larval grubs of the carrot fly.
The problem with controlling pests and diseases on herbs, like vegetables, is that they are likely to be required for eating a short time afterwards, so a suitable chemical must be chosen which will leave the plants safe for consumption one or two days after spraying. Many of the products containing per-methrin are suitable or you could safely use a soap-based organic spray.
There is no satisfactory remedy for mint rust, except to dig up and burn or otherwise safely dispose of affected plants, and start again elsewhere in the garden, with new, clean stock, preferably from a herb specialist.