Most north European herbs, such as mint, simply die back and re-emerge the following spring. Though more tender, thymes can sit out cold winters, but the likes of bay need help to do so. Needless to say, sub-tropical basil has no chance and must be treated as an annual here.
Loading article content
Lovage and tarragon protect themselves against icy winters by discarding leaf and stem. As days shorten, the plants are triggered into shutting down. The foliage decays, leaving the roots intact, so all we have to do is clear away the vegetation and wait for spring.
During the summer, my hops use lovage's majestic three-metre stems as a climbing frame, so tidying up a mess of tangly hop vines and rotten lovage isn't as easy as it could be. I go a step further in the mint bed by wielding the strimmer to flatten the remaining woody mint stumps and discouraging pernicious weeds.
Ground elder insidiously weaves its way between the herb roots, so can't be dug out. With some northern toughies, you can extend the season by two or three weeks by digging up and potting a clump of your favourite mint or chives. Although the timing of dormancy is largely controlled by day length, temperature also plays a part. The greater warmth of the greenhouse or a kitchen sill tricks the herbs into continuing a little longer. But you will find they have much less flavour than usual, so you might want to use precious greenhouse space for more needy specimens.
Some tender herbs, such as rosemary and bay, must be squeezed into the greenhouse. They might survive a mild winter, but I'm not prepared to take the risk. My bay tree is so large it takes some moving, so a few years ago I left it against a south-facing wall for the winter to be left with half the shrub in spring. Lesson learned.
Other woody Mediterranean plants - such as thyme and winter savory - can cope outdoors in the open ground, provided the soil is very free-draining. They grow naturally in gritty Mediterranean hillsides so won't tolerate soggy soils. But you must be more careful when growing them in containers. Apart from a thin icy topcoat in the depths of winter, soil temperature rarely drops below 5C between December and February. But the compost in a pot quickly gains or loses heat through its wall: it could easily become rock hard. To prevent this, group containers together and run a thick layer of bubblewrap round them.
Bubblewrap becomes indispensible at this time of year. Instead of digging up sorrel and moving a clump to the greenhouse, the simplest way of enjoying its tangy, lemony flavour a bit longer is to stick a cloche over a plant. Or use two or three large twigs to support some fleece. You might also get away with a final sowing of salad rocket under a cloche. You'd need to sow thickly as germination rates are getting very low now, but salad rocket should appear within a week and you can start cutting when it's 7cm-8cm tall. You would get better results in a greenhouse or polytunnel, though.
As I said last week, I'm all for tidiness in much of the garden, but some herbs should be spared the strimmer. Because the large umbels of dill and fennel provide shelter for countless insects, they're a magnet for blue tits and chiffchaffs. Enjoy the antics of these tiny birds clambering among the flower heads while you're also cutting back on your feed bill.