Crocus: Herald of Spring

Published: October 6, 2020

"A single crocus blossom ought to be enough to convince our heart that springtime, no matter how predictable, is somehow a gift." – David Steindl-Rast

Although we have yet to endure the rigors of winter, in only four short months the small, cup-like flowers of crocus will begin to appear. The arrival of this herald of spring is an eagerly anticipated sign that the end of winter is in sight. However, a bit of advanced planning is necessary for gardeners to experience this joyful event. October is an ideal month to plant this resilient little flower whose appearance announces that springtime soon will follow.

While crocuses do not produce the overwhelming spectacles of color as do daffodils and tulips, their earliness, durability and ease-of-growth makes them useful garden flowers. Fall planting of crocus and the other spring-flowering bulbs is essential in to allow time for the establishment of a good root system, followed by the requisite chilling period needed to induce flowering.

Crocus is genus of perennial flowering plants belonging to the Iridaceae (iris) family. The genus name genus is derived from the Greek word krokos, which ultimately can be traced back to kumkumam, the Sanskrit word for saffron. The spice saffron is obtained from the orange-red stigmas and styles ("threads") of Crocus sativus, a fall-blooming species with lilac or white flowers. Saffron is one of the most expensive spices in the world today. This is not surprising, given the fact it requires over 4,000 dried crocus threads (all harvested by hand) to produce one ounce of the spice.

The exact origin of crocus remains a mystery. However, the history of crocus cultivation dates back to the Bronze Age. The Egyptians, Greeks, and Aegean Minoans (2100-1600 B.C.) all grew crocus primarily as a source of saffron, used as a coloring agent or to flavor food. Crocus (or saffron derived from it) also was used medicinally by ancient Egyptians. Even today, saffron is used as an alternative medicine by some to treat ailments ranging from anxiety to whooping cough.

Often referred to as one of the "Dutch bulbs," crocus was introduced to the Netherlands in the mid-sixteenth century from corms brought back from the Roman Empire. By early in the seventeenth century, new garden cultivars of crocus had been developed, similar to varieties still on the market. Today, the large-flowered, Dutch hybrids predominate the crocus market.

Although crocus is considered a spring-flowering bulb plant, its overwintering storage structure botanically is known as a "corm" and is the same type of structure produced by gladiolus. Quite versatile as an ornamental, crocus may be planted in many locations in the landscape. It will often grow and flower well under deciduous trees, since crocus develops early enough in the season that much of its annual growth cycle is completed before shade becomes dense enough to reduce growth. However, root competition under trees can be a problem and plants might not develop as rapidly as in a sunny, more desirable location.

Crocus should be planted in rich soil with very good drainage. It can tolerate fairly heavy soils if established in raised beds or berms that help prevent water accumulation around the corms. Crocus is an excellent in rock gardens or perennial borders. Since the flowers of most types are only a few inches tall, it needs to be planted where it is not hidden by taller plants or structures. Crocus also naturalizes well and can be established in low grass which is not too dense, usually in light shade.

The grass-like leaves of crocus are produced in very early spring but do not expand until after flowering has occurred. Foliage must be allowed to mature fully and die-back naturally before being removed. If the leaves are cut off too soon, the development of the corms will be incomplete and, even though the plant might not die, it likely will not have stored enough food to promote flowering in future years. For this reason, do not attempt to naturalize crocus in lawns that require mowing in early spring.

Over 70 species of crocus exist in nature, however, most are not available to home gardeners. As mentioned previously, the Dutch hybrids are the most popular type of crocus in the gardening world today. They develop the largest flowers of any crocus and come in many colors including blue, purple, yellow, white and striped. However, the Dutch hybrids are among the latest to bloom of the common crocus. Some species and their cultivars with smaller but earlier flowers (e.g. Crocus sieberi or C. tommasinianus) are available and sought after by those who want the first sign of spring as early as possible.

Since a single crocus flower is quite small, the most colorful display comes from using many corms planted fairly close in proximity to one another. Depending on the effect wanted, space crocus corms from two to four inches apart. Gardeners who would like a striking display of flowers during the first season of bloom after planting must space more closely. Alternatively, corms spaced farther apart, in time, will form clumps with multiple flowers to produce a larger display of color. Whatever spacing is employed, a grouping of one type and color will provide a more eye-catching display than a mixture of different types and colors.

Plant crocus corms two to three inches deep. In heavy soils, shallow planting is best whereas in loose, sandy soils the deeper planting depth is preferred. In locations with heavy soils that are frequently exposed to freezing and thawing during the winter or early spring, crocus corms are sometimes "heaved" up and out of the ground. To prevent this, the area into which corms have been planted should be covered with an organic mulch that keeps the soil at a more uniform temperature. In late winter, it is a good idea to check a crocus planting to make sure none of the corms have heaved out of the soil. If they have, they can be gently pushed back. If not promptly found and firmed back into the soil, they will dry out and be killed during sunny, warm spring weather.

Crocus also may be grown in pots for flowering indoors by potting the corms in October. Six corms per five-inch pot is considered ideal. During rooting and early development, the pots must be kept cool. This may be done most easily by burying the pots containing corms in a trench outdoors in a shady location. The trench should be filled with straw, sawdust or peat moss so that pots may be removed easily after the ground freezes. After January, the pots may be brought indoors and placed in a cool room to grow and develop for several weeks. When the small flower buds develop enough to show color, they may be moved into a warmer room for display.

Finally, crocuses described in this article should not to be confused with Colchicum autumnale, commonly known as autumn crocus. The latter is a fall-blooming bulb plant which closely resembles common crocus but is a member of the Colchicaceae plant family. Although an attractive ornamental valued for its fall display of color, all parts of autumn crocus contain a very toxic glycoalkaloid called colchicine. Accidental ingestion of autumn crocus can result in severe gastrointestinal side effects in both humans and pets.