Cumin is easier to grow in warmer climates with longer growing seasons. However, a polytunnel can offer gardeners just enough extra warmth, particularly towards the end of the season, to allow warm climate herbs like cumin to get to the stage that they produce seeds. Those seeds can then be used in a wide range of curries and other Asian recipes for an earthy, full flavour and you can impress your friends and family with the range of things you are able to grow at home.
Since cumin has such a long growing season and likes warmth, it is important to start sowing cumin early in the year. You should sow seeds in a warm place or a heated propagator indoors around eight weeks before the last frost date in your area. A couple of weeks after the last frost date the temperatures should have warmed sufficiently for you to harden off your cumin and place them in your polytunnel, either in a pot or in the ground. Cumin can cope with a range of soil conditions but will do best in soil with a neutral pH that is a fertile, free-draining, sandy-loam. If your soil is less than ideal then you will probably have more success growing cumin in a container. If you do plant direct in the soil, maintain a spacing of around 20cm between each plant.
Water cumin regularly but take care not to over water. The soil should be almost dry before you water again, at which point you should soak the area thoroughly. Not only are cumin plants useful for their seeds, which are used in a range of recipes in the kitchen and in some herbal and health remedies, the flowers are also good for attracting beneficial insects, which is why they may be a good addition to your polytunnel.
The plants are not frost hardy so if a frost threatens then you will have to offer your cumin plants some extra protection.
Cumin pods will eventually turn brown. When this happens (usually after around 120 days from sowing) you can remove the heads from the plants. Dry these thoroughly and then open them to retrieve the seeds from inside. Store dried seeds in a jar in a cool, dark place and grind or use as necessary. You will find many uses for this useful warm-weather herb.