Unlike its ornamental cousins which seem to be able to grow anywhere, the Crocus sativus is a tricky plant to grow in the British climate. This is all down to its Mediterranean origins, but by keeping to a few simple rules you should be able to create a perfectly acceptable environment that will produce a successful – although extremely small – crop of saffron spice year on year.
Although its ancestors are now unknown in the wild, the domesticated plant that exists today requires a rich fertile soil that will reliably dry out and even bake during the summer. This hot dry period is vital as it creates the dormancy period required to trigger flower initiation in the autumn.
Traditionally the Saffron crocus was grown in raised containers to guarantee good drainage. This would have given the Tudor gardeners control over the root environment ensuring that the vital dormancy period occurs. In modern European commercial practices, the Saffron crocus is planted into pockets of land that slope towards the sun. That way they get almost all day exposure to the heat and light, as well as the excellent drainage provided from the sloping ground. It makes sense then to place your bulbs in a fully open and sunny site, and planted into a very well-drained soil.
Plant them 6 inches apart, and - unlike most small bulbs - plant them comparatively deep, about 6 inches or so. This planting depth is another critical factor as this can affect the plants spice yields. The current rule of thumb is that the deeper the saffron corm is planted the better the quality of spice is produced. Unfortunately there is also down-side to this as your plants will have fewer flowers and will produce less bulblets for propagation later.
Mice and squirrels can also be a real problem when you are trying to grow crocus as they capable of destroying trays of bulbs in a single night. Dipping the bulbs in liquid paraffin can sometimes work, but covering them with a very fine-mesh wire under the soil is usually the best method.