crocus and colchicum two unique bulbs for autumncrocus and colchicum two unique bulbs for autumn

Crocus vs. Colchicum: Two Unique Bulbs for Autumn

 
By Kimberly Toscano, entomologist, gardening expert and writer.

 

Paint the autumn garden in vivid hues with fall-blooming crocus and autumn crocus. No, that wasn’t a typo. Fall-blooming crocus and autumn crocus are two different plants with similar names - but don’t let that deter you - these little beauties invigorate the fall garden as other plants prepare for winter’s sleep. In case you need one more reason to plant these autumn jewels, both colchicum and crocus provide nectar and pollen late in the season for busy bees and other pollinators. So grab the bulb digger and get planting!

Crocus & Colchiucm: What’s In A Name?

The world of plant names is riddled with homonyms different plants sharing similar common names. When you hear the word “marigold” do you think of the native, sunny yellow Marsh Marigold, or the papery orange and yellow marigold flowers often seen around vegetable gardens? Depending on where you live the name “bluebell” may refer to a native woodland wildflower (Virginia Bluebells), a Mediterranean bulb (Spanish Bluebells), or a desert annual wildflower (California Bluebell). No wonder plant nerds use botanical names!

When it comes to bulbs, the name “crocus” is often used to describe two unrelated plants: Colchicum, often called by the common name autumn crocus, is a Lily relative, while true Crocuses belong to the Iris family. True Crocuses include the popular spring-blooming varieties that mark winter’s end, fall-blooming species, and the Saffron Crocus used in cooking.

So why do they share the same name? Because looks can be deceiving. Both bulbs produce large, chalice-like blooms in shades of lilac, pink, violet, and white. And both include varieties that bloom in autumn as the summer garden fades. Fortunately, the two plants share similar needs, so even in the case of mistaken identity gardeners have found success. Still, here at American Meadows, we use the botanical name Colchicum to avoid confusion.

chart showing the difference between colchicum and crocuschart showing the difference between colchicum and crocus

What’s the Difference?

While the flowers of the two plants look similar, there are some notable differences between the two groups.

Bulbs: 

  • Both true Crocus and Colchicum grow from corms, not true bulbs.
  • The corms of Colchicum tend to be larger than crocus. As such, they have different planting requirements. The larger Colchicums are planted at a depth of 4 to 6 inches, with an equal spacing, or about 4 plants per square foot.
  • Crocus corms are planted at only 2 to 3 inches deep and spaced 2 to 3 inches apart, for about 12 corms per square foot.

Foliage: 

  • Colchicum flowers appear naked, that is the blooms emerge separately from the foliage. Colchicum leaves appear in spring and are large and floppy, looking quite at home among hostas.
  • Fall-blooming crocus has narrow, grass-like foliage that appears either in autumn or in the spring, depending on the species. Spring-blooming varieties flower at the same time foliage emerges.

Flowers: 

  • The flowers of Colchicum are typically larger than those of Crocus and each corm produces 5 to 10 stalks each bearing a single flower. These showy blooms grab your attention from across the garden.
  • Crocus blooms are daintier with fewer blooms per corm, but have lovely detail when viewed up close.
  • The two groups bloom September through November, with some crocus varieties blooming as late as December.

Hardiness & Plant Needs: 

  • Colchicum tend to tolerate colder winter temperatures (Zones 4-10).
  • Fall-blooming crocus is hardy to Zones 6-10, with the exception of Saffron Crocus, which is hardy to zone 4
  • Colchicum is more tolerant of partial shade, while Crocus prefers sunny locations.

 

How to Use Crocus and Colchicum in Your Landscape

Both Colchicum and Crocus benefit from rich, well-drained soils. Drainage is particularly important during the summer months when bulbs are dormant, which is also the time most gardeners irrigate beds. Poor drainage can lead to rotting bulbs. Rock and herb gardens make ideal planting sites, as do raised beds and perennial borders. Planting corms on berms and mounds can help improve drainage in planting beds that are not raised. Both can also be planted in containers for stunning autumn displays or forced indoors for winter color. 

Tuck groups of bulbs in pockets to add fall color to perennial beds or try planting the corms among low-growing groundcovers such as Creeping Thyme or Creeping Jenny. The showy blooms will easily push through the low canopy and light mulch layers.

Colchicum and Crocus naturalize well in meadows or woodland edges, however, they must not be mowed until the foliage dies back. Plant in large drifts for a natural appearance. Avoid planting in locations where the flowers will be hidden by falling leaves in autumn.


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Planting Tips for Crocus and Colchicum

Colchicum and fall-blooming Crocus corms are planted much earlier than spring-blooming bulbs. Corms are shipped in August and should be planted as soon as they arrive. For more information, see our guide, How To Grow Fall Flowering Crocus.

Best Companion Plants for Crocus and Colchicum

Plant combinations for these autumn beauties are countless. A few considerations will help in selecting the best planting site. The blooms of both Crocus and colchicum are low to the ground, so be sure to place them where they can be enjoyed and not hidden by larger plants. While Crocus has attractive, low-growing foliage, the spring-time leaves of colchicum are broad and tall. Be sure plants are located such that spring foliage does not hide smaller, spring-blooming bulbs.

Also remember, like all bulbs, it is best to leave the fading foliage in place as it dies to replenish the corms. Colchicum can produce rather unattractive foliage as it dies back late spring-early summer. Try hiding it among hardy geraniums, dwarf hostas, or hellebores. Hint: these plants can always be trimmed back to uncover blooms in fall.

Vining groundcovers support the weak stems of colchicum and lift them from the ground, often increasing flower life. Crocus also look lovely poking through groundcovers. Try planting corms among sedums, periwinkle, creeping jenny, creeping thyme, or bugleweed.

In sunny locations, pair crocus with sedum, dahlia, or helianthus. Pockets of sun in woodland gardens are great places to tuck colchicum. Plant it among heuchera, astilbe, tiarella, lungworts, and primrose. Both crocus and colchicum work well in combination with asters and chrysanthemums for a dynamic autumn display.

Finally, crocus and colchicum make a brilliant carpet when massed beneath showy shrubs and specimen trees. Accent the autumn blooms, berries, and foliage of dogwoods, beautyberry, viburnums, and witch hazel with vibrant blooms.

 

A Word of Caution

All parts of colchicum are poisonous to ingest. This is important to note due to the fact that saffron crocus is a food crop. While the flowers of crocus and colchicum are readily distinguishable, it is best to grow edible saffron crocus in a different location from colchicum to avoid any potential for misidentification. The good news is that the toxins in colchicum make them critter-proof.

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