Caren White is a Master Gardener and instructor at Home Gardeners School. She has been associated with Rutgers Gardens for over a decade.
In most areas of the country, crocuses provide the first pop of color in the spring. They have even been known to grow and flower in the snow.
What are Crocus?
Crocus (Crocus vernus) are perennial plants that are native to the Mediterranean, Middle East and Southern Asia. They were introduced in the Netherlands in the 16th century and from there spread all over Europe. European colonists brought them to the New World in the 17th and 18th centuries. They are hardy in zones 3 – 8.
Crocus are often called spring bulbs, but they actually grow from corms, not bulbs. Bulbs contain an embryo in the center surrounded by food for it. If you cut a bulb open, you will see layers protecting the embryo. A corm, on the other hand, is all food, no layers. The embryo resides in the top of the corm rather than in the middle like bulbs.
Crocus are small, only 3 to 6 inches tall depending on the variety. The earliest bloomers, the so-called snow crocus, appear in late winter while the later ones, often referred to as Dutch crocus, start growing in early spring.
The leaves are thin and strap-like, resembling grass. They are bright green with a white stripe running along the length of the leaves. The flowers are bell shape and can be white, lavender, yellow or purple. There are also bicolors and tricolors.
When to Plant Crocus
Crocus are planted in the fall because they need a 12 to 15 week period of cold weather (35⁰F to 45⁰F) to stimulate them to grow and bloom. In general, in the northern parts of the US, the corms are planted in September and October, while in the southern parts of the US, they are planted in October and November. The best indicator of when to plant your corms is 6 to 8 weeks before a hard frost when your soil cools off to less than 60⁰F.
In my zone 6 NJ garden, I always wait until November to plant my spring flowering bulbs. Due to climate change, our fall is now so warm, that the soil doesn’t cool down until then. If I plant my spring flowering bulbs in September or October while the soil is still warm, they immediately start growing, instead of remaining dormant until spring.
In warmer parts of the south such as northern Florida, the weather and the soil never gets cool enough to provide the corms with the needed 12 to 15 weeks of cold weather. In that case, gardeners chill their corms in their refrigerators for 12 to 15 weeks before planting them in late December to early January when the outdoor temperatures are still cool and before the heat of spring and summer.
How to Plant Crocus
Crocus are very easy to plant. Just dig a shallow hole, 3 to 4 inches deep, place the corm at the bottom of the hole with the pointy end facing upwards. That is where the embryo resides that will grow into the plant. There is no need for fertilizer. The corm stores all of the food that the embryo needs to grow.
Crocuses are tiny, so planting them singly around your garden doesn’t look like much in the spring. They are better planted 2 to 3 inches apart in large groups of 10 or more. They have more of an impact in large groups or drifts if you are feeling ambitious and have the space. They also naturalize easily so they can be planted in lawns and woodlands. You can plant them under deciduous trees because they grow and bloom before the tree’s foliage comes out and creates shade. Don’t plant crocus under evergreens. Evergreens never lose their foliage so it is always shady underneath.
It is best to plant multiple varieties of crocus to ensure a long season of color. Rather than buying them at a big box store where you don’t know what kind you are getting, order from a catalog such as Brecks or John Scheepers Beauty From Bulbs. There the corms are listed individually, indicating bloom time, bloom color and plant size. You can order specific colors or get a mixture of colors.
What To Do When Crocus Finish Blooming
After your crocus finish blooming don’t cut their leaves down while they are still green. The leaves are busy photosynthesizing sunlight and storing food for next year in the corm. If you have planted crocus in your lawn, do not mow your lawn for at least 6 weeks after the plants finish blooming to give the leaves the maximum amount of time to create and store food for next year. Without that food, the plants will not have the energy to grow and bloom next spring. After the foliage has turned brown, it is safe to cut it down in the garden or mow your lawn.
How to Prevent Pests From Eating Crocus
Deer don’t bother crocus very much, but small rodents such as squirrels, rabbits and voles love the corms. The best way to keep them from digging them up and eating them is chicken wire. You can either lay the chicken wire on the surface of the soil over the corms or you can plant the corms in chicken wire cages.
I don’t have a problem with animals digging up and eating my crocus in the spring. My enemy is squirrels in the fall. They always find the bulbs that I have planted. I did some research and discovered that they can smell freshly dug soil. They then dig into that earth to see what is buried there. So another reason that I wait until November to plant my spring flowering bulbs is by that time most of the leaves have fallen from the trees and into my garden. After I plant my bulbs, I cover the area with leaves which masks the scent of the freshly dug soil.
How to Divide Crocus
Crocus “naturalize” easily meaning they reproduce readily from seed that is dropped into the soil after the flowers have finished. This results in new corms and new plants. Eventually the plants become overcrowded and produce fewer flowers. It’s time to divide your crocus!
After the foliage has died, use a garden fork to carefully dig up the corms. Brush the dirt off of them but don’t wash them. You don’t want them to get wet and possibly rot. Discard any old or diseased corms and plant the remaining ones 2 to 3 inches apart in groups of 10 or more or in large drifts.
© 2019 Caren White
Caren White (author) on April 06, 2019:
Lorelei, that's a great idea to plant early blooming flowers for the bees. You are right that they need a lot of help these days.
Lorelei Cohen from Canada on April 06, 2019:
I saw a bee searching our yard a couple days ago for flowers and immediately thought that I should plant crocus flowers as they bloom very early in the year. Bees currently need all the help they can get. The rest of the year we have pretty much covered with our fruit trees and berry bushes.