Saffron - Crocus Sativus has been cultivated for its valuable stigma for over 3000 years. Each flower has three red stigma (or threads) which droop out from the centre of the flower. These have been used since ancient times in cosmetics, perfumery, cooking and traditional remedies.
Growing saffron is a delicate balancing act. It requires cold winters, hot summers, low humidity, just the right amount of rainfall (or irrigation) and the right type of friable free-draining soil. The areas in New Zealand ticking all these boxes are probably only Central Otago, Marlborough and Nelson. However, with a harvest so valuable it could be worth planting out a few rows in areas that potentially have a suitable microclimate.
Saffron is grown from a corm (or bulb) which should be planted in its dormant period over summer. Prepare the soil by working in fertiliser (such as blood and bone) and working it up into raised beds. Soil type needs to be loose and friable with a high nutrient content to allow effortless root penetration.
Plant the corms 10cm deep and 10 - 15cm apart in the raised beds. Purchase good quality large corms, they will produce dozens of daughter corms over following years. The more corms you have the more flowers you'll produce. Each corm produces between 6 and 12 flowers in a season and the original size of your corm dictates the size of its daughters and the quantity of flowers it produces.
Saffron flowers in its first season of planting. Flowering starts in the first week of April and lasts around 5 - 6 weeks. The majority of flowers will arrive in an intensive 3 week period starting in the middle of April. Each flower must be picked within 48 hours of appearing. Ideally picking is done early in the day after the dew dries and before the sun begins to wilt the flowers.
It takes around 150,000 flowers (or 450,000 threads) to produce a kilogram of dried saffron, depending on the quality of the flowers. This number of flowers needed could be as high as 200,000 flowers for smaller, poorer quality flowers.
The yield you can expect per hectare is dependent how long the corms have been in ground producing daughters and on the growing and environmental conditions. If you have had the corms in for around 4 years and all the conditions are ideal, you might get as high as 24 kilos of saffron per hectare. If conditions aren't ideal you could get as little as 2.5 kilos (or none if conditions are completely unsuitable).
Once the flower is picked it is vital they are dried as quickly as possible to retain quality threads. Drying can be done with a dehydrator, hot air flow or freeze drying. All methods have their benefits but the most important thing is to dry as quickly as possible and not to over dry. 10% moisture will ensure quality long-term storage and a product which retains its colour, flavour and aroma.
Saffron needs fertilising once or twice a year and the beds should be kept weed free. Mulching the beds with sawdust helps with weed control. Every few years the corms need to be lifted - they become overcrowded and affect the crop yield as they compete for diminishing space. They also tend to grow on top of one another diminishing the space between the soil and the surface. Keeping the crop watered is important for producing quality flowers. However, take care not to over water - it will deter flowering and increase humidity causing fungal disease. Watering the crop just before flowering helps to produce larger flowers - yielding larger (heavier) threads.
Care needs to be taken to protect the corms from predators such as rabbits and rats. They can dig up and eat the precious bulbs during the plants dormant season.
Harvesting saffron is very, very labour intensive and it is this that contributes to saffron being the world's most expensive spice.