The clue is in the name. Basil is from the Greek for royal and the full Latin name Ocimum basilicum translates roughly as ‘to smell like a king’. This summer herb has always been prized for its rich aroma, and as suited to a simple peasant lunch as a kingly banquet.
First, a note about pots of supermarket basil. I can’t count the number of people who have told me they haven’t got green fingers because they can’t even keep their supermarket basil plants alive. Please know that these plants are only designed to last two to three weeks in the home; the compost only has nutrient for that long, the seeds are sown too dense to grow into larger plants and they have been grown to that size in perfect, glasshouse conditions before spending a week in a dark pack house/supermarket then a windowsill in your house. Buy them, eat them, then learn how to grow your own! Or give the plants a chance to grow by splitting them and repotting into fresh, quality multi-purpose compost as described here.
Grow from seed
For the most cost effective crop, grow from seed. A few seeds scattered on potting compost in May will soon germinate. As they grow, you can thin them (you can wait until they have their first true leaves, then eat the thinnings), leaving one plant per 9cm pot. The secret to a long lasting, bushy plant is to keep pinching out (and eating) the tips, meaning the last couple of leaves and the growing point from every shoot. This will cause the plant to make lots of side branches. Even though they are prone to running to seed (flowering), constantly taking out the flower shoots will keep the lush leaves coming. In this way, I have kept outdoor basil plants alive for the whole of the summer. They are not frost hardy though and dislike cold weather so by mid September I cut whatever is left and make batches of pesto to freeze for the winter.
Last year I grew 6 very different types for comparison. ‘Greek’ basil makes a beautifully compact plant that would look lovely in a pot – from a distance it looked like a perfectly trimmed box ball. I almost didn’t want to harvest any as that would have ruined it’s perfectly spherical form, but eventually settled on giving each plant an all over trim in sequence, just like a box ball. The flavour was milder and peppery than traditional basil.
There were two purple varieties, ‘Ararat’ and ‘Dark Opal’. The former was more mottled purple/dark green and quicker to flower, but the ‘Dark Opal’ was so deep purple it was almost black, which makes a fantastic foil for other herbs (think of it with yellow oregano, pink flowered thymes and feathery green chervil). It was also very slow to run to seed. Both of these types had a pronounced aniseed flavour that would work well in Thai curries.
Two of the more traditional varieties are ‘Napoli’ and ‘Sweet Genovese’. These are classic Italian basils, the latter being very similar to the supermarket types. ‘Napoli’ is notable for the size of its leaves – each one would be big enough to fill a sandwich. Both these types fared well in our taste test – very aromatic, traditional flavour and excellent for pesto. The final variety I grew was called British Bush. Bred to be more cold tolerant, it stood much better through September than the other varieties. The results in the taste test were less positive though, with an odd flavour, more like camphor with hints of basil to it. Good if you live in a cold region and want to grow basil, but if you have the option, I would just grow more of the Italian types and get good at batch freezing pesto.