Taxonomy and Plant Type
Taxonomy places crocus bulbs in the genus Crocus. Since the common name and scientific name are, then, the same in this case, I distinguish between them by capitalizing only when referring to the genus name. Don't confuse them with the Pasque flower relative nicknamed "prairie crocus."
Crocus plants are relatively small, reaching just 3-6 inches in height (depending on the variety). The leaves are grass-like, generally with a light stripe running up the middle. Many of the spring-flowering crocuses are among the earliest bloomers (C. vernus tends to bloom a bit later), flowering even before Scilla siberica. The crocus bulbs with which I'm familiar produce multiple flowers per corm. Typical flower colors are yellow, gold, purple, white and lavender, although bi-colored and tri-colored types also exist. The blooms pucker up at night (and also when it's cold and/or cloudy).
Planting Zones, Sun and Soil Requirements
Grow crocuses in full to partial sun and in a friable, well-drained soil.
The light requirement isn't as difficult to meet in this case as it is for many sun-lovers, since crocus flowers bloom in spring, meaning they can be grown under deciduous trees.
Crocus flowers get enough sun in the spring (before the trees leaf out) to grow and acquire the nutrients they need for the growing season. But don't grow them under evergreen trees, since the latter cast shade during the entire year and would deprive your crocus plants of the necessary springtime sunlight.
Types of Crocus Bulbs
The name derives from the Greek for "saffron." Indeed, saffron is harvested from the stigmas of one particular type of crocus: C. sativus. C. sativus, like Colchicum autumnale (different genus but bearing a striking resemblance) and similar plants, is one of the fall-blooming crocuses. It is planted in spring or summer, unlike the spring-blooming types (which are planted in fall).
Spring-blooming types include:
- C. vernus
- C. chrysanthus
- C. tommasinianus
- C. sieberi
Problem is, if you buy them from a home improvement chain store in the U.S., you won't necessarily know exactly what it is you're planting, as the scientific plant name may not be included.
When to Plant Crocus Bulbs
Spring-blooming types are planted in autumn (the colder your climate, the earlier in the fall you plant), while fall-blooming types are planted in spring. To find out when you should be planting the spring-blooming types in your particular region, see the zone-based schedule that I provide in Spring Bulb Plants.
How to Plant Crocus Bulbs
Plant 2 inches deep and provide 2-3 inches of spacing. The pointy part should face up. Some fertilize at planting time with bone meal. Others say bone meal is unnecessary at this time and invites pests to dig around, which could dislodge your crocus bulbs.
If this is a concern, lay chicken wire on top of the ground after planting. Or you could hold off on the bone meal till spring and just use some compost when planting.
Divide to prevent overcrowding and/or to propagate.
For the sake of plant nutrition, leave the foliage alone after blooming until it fully yellows. If you're growing your plants in a planting bed, it's easy to leave them alone for this time period. But if you're growing crocus flowers in the lawn, it may be difficult to remember that you won't be able to mow until the foliage yellows (about 6 weeks after bloom). That's because the leaves are so grass-like that they blend in to lawns. To help yourself remember not to mow in that area, stick stakes in the ground as the blooms of your plants start to fade, to mark the "no-mow zone."
Landscape Uses, Squirrel Control
Squirrel pests like to dig up crocus bulbs. Spreading blood meal around the planting bed will help deter the pests (and green up the grass considerably, if you're planting crocus bulbs in a lawn area), but a surer squirrel-control method is to lay chicken wire on top of the ground where you have just planted your crocus bulbs. The nice thing about protecting crocus bulbs in this way is that, since crocus plants are relatively small, there's no need to remove the chicken wire later, unless it's an area you'll need to mow (for bulb plants that grow bigger, you'd have to remove the chicken wire before they push up in spring, lest the foliage be cut on the sharp wire).
Rabbits present a challenge in growing crocus, too, because this spring bulb is one of the plants that rabbits eat. These pests will treat the above-ground growth as if it were part of a salad bar. For quick rabbit control, you can apply BirdBlock over your plants, but this netting spoils the overall effect. I recommend planning ahead, instead, and setting up a rabbit-proof fence.