How to Grow Saffron Crocus. Saffron crocus is a highly attractive herb which produces lavender or purple flowers in the fall after other plants have declined. That is reason enough to grow the herb, but perhaps an ever better reason is that it is the world's most expensive spice. Because the popular Spanish seasoning costs anywhere from $500 to $5,000 a pound, it makes sense to grow some of your own.
Find saffron crocus at a garden center or order them from a gardening catalog. Saffron crocus plants must be started from a bulb, called a crom. While they may be hard to find in many stores, they are readily available by mail order.
Improve the soil where you'll grow the saffron with some organic material. Saffron thrives in rich soil, so mix in some compost or other organic material, such as leaves or grass clippings, into the soil.
Plant the croms in the spring or fall. If planted in the fall, the crocuses will sprout the following spring.
Dig a 4-inch hole and place the croms into the hole with the roots pointing downward. The croms should be spaced 4-inches apart as well. The freshness of the crocuses is vital, so plant them soon as danger of frost has passed. Because each plant produces only a small amount of saffron, it is a good idea to plant an entire row of saffron crocuses.
Keep the soil dry during the summer, but water more often in the fall. Saffron crocuses are dormant during the summer and should be kept dry. However, when they come to life in the fall, they do need occasional watering to keep the soil from drying out.
Grow saffron crocus as a perennial in USDA zones six and higher. In zones below six, the crocuses may not survive the winter. Improve their chances by applying a thick layer of mulch over them during the winter. Go to the National Arboretum website and choose "USDA Plant Zone Hardiness Map" from the "Research Activities" menu for details on hardiness zones.
Bring saffron crocus croms inside in cold climates. Dig the bulbs up after the foliage has died, place them in a plastic bag along with some peat moss and store them in a cool, dark place like a basement. Replant them the following spring.