They say that saffron is the most expensive spice in the world, gram for gram. Historically and indeed in the present day, it is much-prized for the golden yellow colour it adds to food or cloth, and for its warm sunshiney aroma.
Its high price by weight is partly because the saffron threads barely weigh anything: you need around 450 filaments to yield a single gram. It's also labour-intensive to harvest: the three long red stigma (below) are the parts of the flower that are picked and all saffron is gathered by hand.
Saffron originated in the Eastern Mediterranean, probably in Iran, which remains the largest producer of the spice in the world today. While it likes the bright Mediterranean sunshine, saffron grows perfectly well outside in the UK given a sunny position. It's also an attractive, with pretty striped mauve flowers, golden yellow anthers and the distinctive red stigmas.
You cannot just harvest any old crocus, however: not all crocus stigma are edible and some are poisonous. You need the long red filaments from Crocus sativus, or saffron crocus. It's an autumn-flowering variety which lies dormant for much of the rest of the year.
For that reason I grow mine in a large container, an old discarded water tank. If I had them in the open ground it would be all too easy to let the area become overgrown with weeds, or, worse, to forget about the crocus and start trying to grow something else in the space.
Growing in a container also means you can ensure it's the in right place, which in this case, means the sunniest spot on the allotment but also one that is fairly sheltered. The saffron crocus bulbs like to bake all summer long before throwing up leaves and flower buds in September/October. They also like well-drained soil: easier to control in the container which has gravel lining the bottom, then layers of multi-purpose compost before a surface layer of topsoil.
Each bulb, or more accurately, each corm, will throw up one flower in a season, so you need plenty of plants to start off with. The corms will, however, divide in following years, so your stock should increase so long as the plants survive.
The bare corms are generally available in mid to late summer. Plant each one about 10cm deep, pointy end facing upwards, and leave 15cm or so between them. You may well have to protect the bed from birds and squirrels who like to dig the corms up. I initially thought this would only be an issue while the bulbs were establishing but it turns out that they will happily dig for crocus corms at any time. So my plants grow through black narrow mesh netting stretched across the top of the old water tank and stapled into place.
Once planted out and protected from foragers, you can pretty well leave them alone. They're perfectly hardy in a UK winter. I got a few flowers to harvest in my first year, but in year two they started producing much more prolifically. The leaves die down completely over winter so your saffron bed will be bare throughout the summer until the shoots start poking through the soil surface again in August/September.
Once the flowers start to come, you should harvest while the red stigmas are just showing, and on a dry morning: in the wet all that lovely golden pigment starts leaching out. Carefully pull them away at the base - this, finally, is where I have found a use for the teeny-tiny tweezers in my Swiss Army knife.
The threads need to dry out before being stored for culinary use. Optimally, this should be done in a warm place, even over gentle heat - Aga owners have an ideal saffron dryer. The rest of us can use the airing cupboard. Once dried, the saffron can be stored in an airtight container such as a small jar, in the a dark cool cupboard, and a pinch used for flavouring paellas, sauce, rice and so on as needed.