Growing from bulb-like structures called corms, crocuses are low-growing perennial plants from the iris (Iridaceae) family. In many regions, crocus flowers (Crocus spp.) mark the arrival of spring. These early bloomers can often be seen peeking up through the snow well before any other flowers appear on the landscape. They grow in a range of conditions, including woodlands, coastal gardens, and suburban lawns. Bloom colors on the tube-shaped flowers include mauve, lavender, and yellow. There are more than 80 crocus species, but most of the bulbs available commercially are hybrids derived from careful cross-breeding of selected species.
While crocuses are often considered bulbs, strictly speaking they are corms, as are gladiolas. The difference is rather technical and not important for most gardeners, since both corms and bulbs are essentially modified storage structures by which the plant will initiate growth. Corms differ from true bulbs in that the corm is modified stem tissue, while a true bulb is modified leaf tissue.
Crocuses are most often planted for early spring color, though there are also varieties that bloom in late fall and early winter. Spring-blooming crocuses should be planted in the early fall. They have a fast growth rate and typically bloom in two to five weeks after the temperature rises and the bulbs begin active growth in spring.
|Botanical Name||Crocus spp.|
|Plant Type||Perennial bulb|
|Mature Size||6 inches tall, 1 to 3 inches wide|
|Sun Exposure||Full sun to part sun|
|Soil Type||Any well-draining soil|
|Soil pH||Neutral (6.0 to 7.0)|
|Flower Color||Purple, blue, yellow, orange, pink, white|
|Hardiness Zones||3 to 8 (USDA)|
|Native Area||Europe, North Africa, Asia|
|Toxicity||Toxic to pets|
Plant crocus corms about 4 inches deep and 2 to 4 inches apart with the pointed end up. Sometimes it can be difficult to tell which is the pointed end. If you can't, don't worry about it too much; the plant will grow toward the light. Adding some bulb food or bone meal to the soil will ensure the plants have all the nutrients they need to get started.
To extend the bloom time, mix different species of crocuses in your garden. In addition, planting them where other plants will fill in and hide their foliage will help to prolong blooming and give the crocuses a chance to store energy for the next season. Crocuses fade quickly once the weather gets hot.
As with tulips and other bulbs, crocus bulbs are nourished by the dying foliage of the plants, so it's important not to trim the leaves until they are completely yellow. This typically occurs within six weeks after the bloom. If the crocus are planted in a grassy area, refrain from mowing during this time, lest your bulbs be deprived of essential nutrients.
Crocuses do best in full sun. But because they bloom so early in the year when there is little foliage on the trees, spots that are shady during the summer are usually fine for spring-blooming crocuses.
Crocus plants prefer a neutral soil pH of 6 .0 to 7.0, and they're usually not fussy about the soil type. But a well-draining soil is crucial. As with most plants with bulb roots, crocuses do not like to sit in soggy soil, which can cause them to rot.
Crocuses are generally low-maintenance plants. They like to be watered regularly in the spring and fall. If there is no snow cover, the bulbs will also need water throughout the winter. However, they go dormant in the summer and prefer drier soil during this time.
Temperature and Humidity
Crocus bulb hardiness varies slightly depending on which type you are growing, but most crocuses are reliable within USDA hardiness zones 3 to 8. They bloom and survive best where winters are cold since crocus bulbs need a 12- to 15-week period of cold temperatures at around 35 to 45 degrees Fahrenheit to set their blooms. Humidity usually isn't an issue, though excessive humidity can lead to rot.
In climates where the winter temperatures are not sufficiently low to chill the corms, crocuses are often planted as annuals, purchased from vendors who prechill the corms at 35 to 45 degrees Fahrenheit for 12 to 14 weeks. It is also possible to chill the corms yourself for the following spring's planting, by digging up the bulbs after the foliage has yellowed. Begin chilling the corms in the refrigerator about 14 weeks before the planned planting time. However, make sure not to store fruit in the same refrigerator, as ethylene gas emitted by the fruit will ruin the crocuses.
Crocuses do not require a lot of fertilizer. They store their own energy in their bulbs, which is why it is essential that you do not cut back the leaves until they turn yellow. However, a light top dressing of bulb food or bone meal in the fall is a good idea if you have poor soil.
- 'Bieberstein's crocus (Crocus speciosus): This species blooms in the fall, featuring lilac blue flowers with dark veining.
- 'Bowles White' crocus (Crocus atticus 'Bowles White'): This variety produces snowy white flowers with yellow throats and blooms in the early spring.
- Dutch crocus (Crocus vernus 'Pickwick'): The flowers of this variety are striped in pale and dark lilac, blooming in the spring.
- Purpureus Grandiflorus crocus (Crocus vernus 'Purpureus Grandiflorus'): This variety blooms in the spring with abundant violet flowers.
- Tricolor crocus (Crocus sieberi 'Tricolor'): This plant blooms in late winter to early spring and features bands of lilac, white, and yellow on its petals.
It is not necessary to divide your crocus plants. In many areas, crocuses are somewhat short-lived, and you might need to replant every few years. However, if your crocuses do very well and start to multiply, they will eventually begin to bloom less as the clumps become dense. If that happens, you can dig up and divide the bulbs when the foliage starts to die back. Replant the bulbs at least 3 inches apart or in another location entirely.
Common Pests and Diseases
Crocuses are susceptible to viruses, which can cause distortions, streaking, and buds that fail to open. There is no cure for viral diseases; if they strike, dispose of the plants to prevent spreading the virus.
But the biggest problem is bulbs and flowers being eaten by chipmunks, deer, rabbits, and squirrels. Other animals, such as skunks, may dig the bulbs out of the ground while searching for insects. There are liquid deterrents that can be sprayed on the leaves and granular deterrents you can scatter to prevent nibbling. You can also buy wire cages or cover the bulbs with chicken wire (under the soil) to protect the bulbs in the ground when you plant them. If you find your plants are constantly being harmed, avoid using bone meal, which can attract animals. Instead, try interplanting your crocuses with daffodils, which animals hate.