Saffron (Crocus sativus) is easily the most expensive spice on the market, which is why it might be a good idea to learn about growing saffron indoors. The care of saffron crocus is no more difficult than that of any other type of bulb. A saffron crocus is just your garden variety autumn crocus; the expense comes in the labor-intensive harvesting of the stigmas, or saffron threads. Each thread must be handpicked at just the most opportune moment; too late and the stigmas will degrade.
How to Grow Saffron Indoors
First, when growing saffron indoors, you’ll want to acquire the bulbs. Make sure you buy from a reputable seed house and that the bulbs are saffron crocus and not autumn meadow crocus — Crocus sativus, not Colchicum autumnale.
Note: To figure out how many corms to order, the general rule of thumb is three threads per person times the number of people in the family times the number of saffron dishes made per year. For example, if a family of four has saffron dishes once every two months or so, they need 24 plants.
Crocus of any sort will rot if planted in wet soil, so planting saffron crocuses inside will ensure the bulb or corms do not rot. Your bulb purveyor will send them to you at the correct time for planting and/or consult with them regarding your climate and location, but they should be planted in the fall.
Lay 1 to 2 inches (2.5-5 cm.) of either fine gravel or coarse sand at the bottom of a 6-inch (15 cm.) planter. Fill the remainder of the container with a rich, well-draining potting medium. Dig a 2 to 3 inch (5-7.5 cm.) hole and place the corm root side down (points facing up!) into it then cover with soil. Space the bulbs 2 to 3 inches (5-7.5 cm.) apart.
Situate the saffron crocuses inside in a cold room of between 35-48 F (2-9 C.), where they will get four to six hours of sun each day. Lightly water the bulbs every other day until the grass-like foliage begins to die back, usually around April. At this time, move the container to a warmer area to simulate spring temps of between 50-70 F (10-21 C.).
Additional Indoor Saffron Care
Watering care of saffron crocus at this stage should be re-initiated. Restart the every-other-day watering regime.
Stigmas from the flowers — there will be three per flower — must be harvested from the blooms the same day they open. Snip open flowers from their stems and tweeze the saffron thread from the bloom, then lay the thread on a paper towel to dry (watch out for breezes or drafts!). Store the threads in an airtight container devoid of moisture. To use your saffron, either toast the strands and then grind into a powder or infuse them in a liquid for use in your favorite paella.
Trim back the foliage only when you are positive the plant is no longer flowering. New buds should break the soil within one to seven days after the first bloom. On occasion, a second (rarely a third) may arise from the same plant.
At this point, stop any irrigation and move the containers of crocus back into the cold room while dormant from April through September. While dormant, do not water the crocus.
Remember, the corms will multiply each year, so eventually, you may have more than you need. Give them to another saffron-lover as a gift. The plants can live up to 15 years, but it’s best to “refresh” them by digging up, dividing, and replanting every four to five years. Be patient; it takes an entire year before the first flowers appear.