Saffron crocuses (Crocus sativus) erupt into bloom in autumn, providing a brief flash of color before the gloom of winter arrives. They are somewhat fussy about their growing conditions, which makes them difficult to grow indoors. Providing the right conditions both above and below the soil line will help increase the likelihood of success, but some saffron crocus corms may fail to grow even under ideal conditions.
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Climate and Temperature
Saffron crocuses originated in the Mediterranean region and will grow outdoors in U.S. Department of Agriculture plant hardiness zones 6 to 8. They do not need a cold period, or vernalization, to set flowers and instead rely on a six-week warm spell during their late summer dormant period. During dormancy, temperatures must stay above 70 degrees Fahrenheit to prompt foliage production and blooming.
Saffron crocuses appear above-ground only briefly from midsummer (when their grassy foliage sprouts) to autumn (when their showy purple flowers bloom).
Container and Soil
Saffron crocuses need plenty of space and soil. Its corms are typically planted 2 to 4 inches deep and 3 to 4 inches apart. Plant individual corms in 6-inch-wide and 8-inch-deep pots, or plant up to five corms in a cross formation in a 12-inch-wide, 8-inch-deep pot. Whatever size pot, make sure it has at least two drainage holes at the base because saffron crocuses will quickly die in wet soil.
Fill the bottom half of the pot with a gritty, fast-draining soil mixture such as equal parts potting soil, milled peat and coarse sand. Arrange corms on the soil with the root end down and the pointed end facing up, and nestle them onto the surface. Cover them with a 2-inch-thick layer of soil.
Use a terracotta or other unglazed clay pot when growing saffron crocuses.
Spring is generally the best time to start autumn-blooming bulbs such as saffron crocuses, although most commercially available bulbs should be planted in late summer as they become available. Once potted, place them within 1 to 2 feet of an unshaded south- or west-facing window with at least eight to 10 hours of direct light each day, preferably more.
Temperatures above 70 degrees are best for growth. Avoid temperatures in excess of 80 degrees because they encourage fast growth, which results in floppy, spindly foliage. Temperatures below 70 will not send the corms into dormancy, which will prevent blooming in autumn. In cooler climates, it may be necessary to place the pot on a heating coil or to cover the pot with a glass cloche to hold in heat. Leave the cloche off for a few hours after watering to limit condensation inside.
Saffron crocuses need very little care throughout the year. Keep the soil dry during the summer when they are dormant, then begin watering in late summer or early autumn when their first sprouts appear. Flood the soil and let it dry out completely before watering again.
Fertilizer is not typically necessary for potted saffron crocuses because it can provide too much nitrogen, which will promote foliage growth over flowering. Simply repot the corms into fresh soil the following spring after the flowers and foliage die back and put them back in their original position. Discontinue watering after midsummer to let the corms go dormant.
During the winter, move the pot in a cool room with bright light to let the corms rest. Maintain temperatures between 40 and 50 degrees F. Water sparingly, barely dampening the soil when it feels nearly dry beneath the surface.
Saffron crocuses have a lifespan of up to 10 to 15 years, during which time they produce additional corms that can be transplanted and used to grow new plants.
Saffron is ready to harvest once the cup-shaped purple flowers open up to reveal their tangerine-orange stigmas, which make up the spice called saffron. Pluck off the little stigmas with a pair of clean tweezers and place them in an airtight container for storage. Use them sparingly to color and flavor cooking.
Do not confuse saffron with the autumn crocus (Colchicum autumnale, USDA zones 4 to 8), which blooms at the same time and resembles saffron crocuses but is highly toxic if eaten.