Herbs have long been valued for their essential oils and near-magical properties. Today, they continue to intrigue, even if the alchemists of yore have been replaced by researchers looking for medicines, food flavourings and face creams.
Scientists isolate the various chemicals in herbs to identify the best growing conditions for the plants. Temperature, day length, the strength of the sun, humidity, soil conditions and moisture levels all affect the growth patterns of plants such as thyme, oregano, peppermint, sage and basil. Unfortunately, from the gardener's point of view, it's not always clear how these factors affect each other and which are the most important.
The chemicals in basil, one of the most popular herbs, vary between species. Mediterranean sweet basil has a strong anise and lilac-orange blossom flavour; eastern European basils have a strong cinnamon tang; while south-east Asian ones are dominated by clove. When choosing which basil to grow, bear in mind that Asian and African ones are much more tender than Mediterranean ones.
Even when growing sweet basil, you should keep the plants warm, dipping no lower overnight than 10-15C, so it's a waste of time growing the plant outdoors, even in a south-facing patio. In the warmer parts of western Scotland, you'll get reasonable results in a polytunnel or a cold greenhouse. Living in the Borders at 200 metres above sea level, I usually need a warm greenhouse, but this year have my basil on the kitchen window sill. Leaf coriander is even more demanding, requiring a minimum daytime temperature of 20C.
Getting the best results from herbs entails providing much more favourable conditions than they experience in the wild. In warmer climes, for example, coriander survives in fairly arid conditions, but it quickly flowers. Wild herbs tend to be packed closely together and have to compete for nutrients with their neighbours, thus limiting their ability to produce flavour-enhancing essential oils. Those oils are actually designed to repel grazing herbivores, and plants that grow well and produce healthy leaves are better able to produce them. So, for best results, provide ideal growing conditions: moist, moderately fertile soil and decent warmth.
Such conditions make plants grow more quickly too – an important consideration, given the length of the Scottish summer. That said, don't be overly kind. Most container-grown plants require liquid fertiliser, but basil and coriander only need a fortnightly feed. To encourage leaf growth, use a general-purpose variety, not tomato feeds designed to encourage flowering and fruiting.
These herbs need moist, not wet, soil. By all means use a saucer to prevent the water from rushing straight through a pot, but remove and empty the saucer after a few minutes. If you put the container on a flat surface, raise the pot slightly off the surface with small batons to let the water drain.
The size of container also affects flavour. Research has shown that individual plants produce more concentrated essential oils when they are more widely spaced. Each basil plant needs two to three litres of compost, coriander one-third of that.
If the summer has persuaded you to garden indoors with basil and coriander, you might be tempted to try more tropical herbs. If you're buying fresh ginger, you may find fat buds on the rhizomes, ready to burst into life. Plant in a 10-litre container, using homemade compost if possible. You'll need a large plant saucer since ginger likes much damper soil than basil or coriander. Because this Asian plant grows naturally in semi shade, it tolerates the lower light levels of south-facing window sills. As with the other herbs, use a general-purpose fertiliser and wait patiently for 10 months till your own ginger rhizomes develop.
Galingal is a much easier plant to grow. You may be able to track it down in Thai or Vietnamese shops. There are several species, all producing a mild ginger flavour. The strong Far Eastern sun probably produces a much hotter flavour. This is a tough, handsome plant with leafy stems that grow to around five feet. With its broad leaves, it fairly fills a corner, but it doesn't produce the large spikes with fragrant creamy flowers you'd get in the Far East. I've had one in a 45-litre pot for seven years. From autumn until spring, it lives in the warm sitting room, spending its summer holidays in the greenhouse. Whenever we hack off a rhizome it readily puts on fresh growth.