Saffron – Should we grow the most expensive spice in the world using CEA?

Zafferano Siciliano Crocus produces large saffron stigmas.

Saffron (Crocus sativus L., a member of the Iridaceae family) is prized for its unique yellow color in culinary dishes and loved by chefs for its flavor in many of our foods. The high cost comes from the fact that it needs to be grown in a particular climate and the long red stigma must be laboriously collected by hand. 

In the US, saffron is traded for up to $10,000 per kilo but this is highly dependent on the final graded product (graded 1- 4, 4 is the best quality and has a high safranal content with the red stigma separated from the yellow anther). The problem is, it takes around 150,000 flowers to produce 1kg of dried saffron. So we want to know, is it really worth it for CEA farmers? Let’s take a closer look at saffron’s history and the pros and cons of growing the most expensive spice in the world.

Ancient artworks revealed saffron was domesticated around 300 to 1600 BC and was thought to have been originally harvested as a mutant of Crocus cartrightianus which was abundant around the time in the Mediterranean.

The origins of saffron agronomy date back to Iran and today the country is responsible for producing over 90% of the world’s saffron where it has both historical and ceremonial importance in Persian culture. Other areas of production stretch across the Mediterranean where conditions are perfect for growing most notably North Africa, Morocco, Spain, Greece, Italy and India. The Spanish love the color in traditional paella whereas the Italians use it for signature risotto dishes like Risotto alla Milanese. 

Visible two to three flowers per saffron corm

Saffron is adapted to arid regions and has an annual life cycle, but it is generally cultivated as a perennial crop by controlling corm bulb growth for the following year. It is a sterile triploid geophyte and is relatively slow to replicate through daughter corms each year. In the field, corms that die back after flowering and unusually have no cold requirement to break their dormancy. They can be lifted from the field during this time and stored in a dry shed before planting out again in spring, although they are hardy and can withstand low soil temperatures. 

Growing saffron in a controlled environment can have many advantages; it’s cleaner, free from pests and disease, nutrients are delivered directly to the root mass, aeration with dissolved oxygen increases biomass, temperature can be maintained without fluctuations and light intensity can be well managed. Saffron needs high intensity light and this can be delivered by high efficiency LEDs without fluctuation, eliminating weather dependent uncertainty in the field. 

Despite the relative ease and low maintenance of growing in a controlled environment, it is the high flower numbers required to produce the end product and subsequent labor intensive ‘picking’ time that are the limiting factor. While in the field it is possible to grow three or more flowers per bulb per season (due to the daughter corms still being attached) the spacing requirements are more difficult to estimate in CEA until trials show optimized growth in a square meter space as smaller daughter corms will produce smaller stigma. We have no knowledge of large scale CEA production data and comparison to field harvests but scaling up in CEA may be more prohibitive due to labor costs. Perhaps automating this process in the future with robotic tweezers or re-engineering tissue culture pickers to use image analysis software with an ability to pick out the red stigma and separate from the anther would be useful, but we are some way off that at present.

Fake saffron is rife within this market and includes corn silk threads, safflower (an unrelated thistle), coconut filaments or even dyed horse hair, or shredded paper. 

Safflower (in tissue culture above) Carthamus tinctorius, is the most likely culprit. It is a highly branched, herbaceous, thistle-like annual plant in the sunflower family Asteraceae and is often substituted for saffron. Each flower head contains 20–180 individual florets that can be confused with saffron to the untrained eye but the color gives it away as they are less intense than saffron stigma. 

Dyes used to color fake saffron will dissipate quickly and this can be tested easily in water. Despite this, safflower has some excellent qualities as an oil in its own right and is commercially traded in the EU. 

A few entrepreneurs are paving the way by growing saffron in CEA. Dr Ardalan Ghilavizadeh pictured above is an expert hydroponics saffron grower from Iran and currently working in Berlin.

Saffron is a short-day plant so requires a period of around 12 hours in the dark and 10-12 hours per day lights on (16-18hrs during flowering). According to Urbanleaf, saffron can be grown indoors and they suggest it will require a DLI of 15+ mols/m²/d to flower. They go on to propose that 24W light bulbs can be placed around 6 inches away from the top of the plants to deliver a PPFD of 500 μmol/m²/s. Ideal temperatures for saffron flowering are around 70°F but anything between 50 and 100°F grows well. We have some preliminary trials with saffron but experimenting with light spectrum may achieve the best results to promote flowering and maintain a stable temperature during flowering. Growing in hydroponics follows similar conditions to other flowering plants and saffron displays a wide pH range of 5.5 – 7 but it’s best stay around 6 for maximum nutrient uptake at EC 1.4. 

Saffron male seed is sterile so it is propagated vegetatively using corms. Flower yield is highly dependent on corm size and density but lack of availability and diversity of plant material presents a major constraint for large scale CEA saffron production. A large corm above 8 grams produces three to four small daughter corms, which take 2 to 3 seasons (in the field a season is one calendar year but in CEA there is potential for four harvests annually) to achieve the size and weight for flowering. 

Forcing the bulbs through regular dormancy periods via CEA may help to promote cormogenesis.

Crocus sativus corms like rock wool for support to protect them against getting too wet. The method of hydroponics i.e. NFT or aeroponics must not allow the bulb to get too wet so it should sit proud of the rock wool substrate. They will root very quickly, around a week in our experience with aeroponic growing. 

Saffron is relatively slow to propagate and only produces a few vegetative corms on the main plant annually in late summer after flowering has finished and the leaves die back. Breeding programs are needed to increase diversity of the corms and micropropagation may provide a solution to access of clean stock material. Saffron research is limited with only a handful of teams working on genetics in India, Iran and Europe. This crop needs preservation of genetic biodiversity to protect its quality and sustainability for future agricultural production. 

Genetic diversity in corm supply is an issue so indirect organogenesis may provide new routes to improve cultivation of saffron. Tissue culture micropropagation, somatic embryogenesis, organogenesis, gene editing and in vitro cormogenesis can all help regenerate pathogen free reproduction of this plant. We are working to perfect this process. 

Harvest first thing in the morning according to Dr Sally Francis, a field grower from Norfolk in the UK. The stigmas must be dried soon after harvest as they can become moldy. Besides the important role that dehydration plays in the preservation of saffron, it is also a necessary process to generate organoleptic properties in fresh stigmas. Dehydration treatment brings about physical and chemical changes necessary to achieve the desired quality of saffron. But be careful drying as over 150F can cause degradation of the phytonutrients.

The high retail value of saffron is maintained on world markets predominantly because of labor intensive harvesting methods but if this was not an issue could growing saffron in a CEA farm give a good profitable return?

The circle of saffron: daughters accumulate after the mother’s die back during dormancy, sometimes there is a large variation in size depending on fertigation. We can achieve this easily in hydroponics applying fertilizer at the correct intervals to increase corm density.

Let’s examine a theoretical scenario growing saffron in CEA reaching the highest market value of $10,000/Kg and play a game of dpi or in this case cpi, corms per inch.

While saffron may not be an obvious choice for most larger commercial CEA growers, it should not be discounted as a high value crop for the service industry, fitting with more niche restaurant based container farms. Saffron is fairly low maintenance until harvest and some are even automating growing, which will reduce labor costs as the stigma can be picked by the restaurants when required without post processing and delivered straight to the chef’s palette. The advantage is it can be grown anywhere, close to restaurants, in cities and of course we are biased but it may also go well with sushi and a side of real wasabi.