To force crocus in a shallow dish, plant the corms shoulder to shoulder with their tips just at the surface of moist potting mix, chill the dish at about 35 to 45°F for 12 to 15 weeks, then bring it into a cool, bright room, where it flowers in roughly two to three weeks. Crocus are small, so a low bowl packed with 10 to 20 corms makes a full, jewel-like display on a table or windowsill.
Spring crocus (Crocus vernus and the smaller snow crocus, C. chrysanthus) bloom low and fast once they get enough cold. Indoors, the big risks are skipping the chill, letting the dish dry out while roots grow, and keeping the bloom in a warm room where flowers open and fade within a couple of days.
Choose the right corms
Buy firm, plump corms with no soft spots or mold, ideally large-flowered Dutch crocus for the biggest blooms. Smaller snow crocus varieties force well too and often flower a little earlier. Plant within a few weeks of buying. If you cannot plant right away, keep corms in a mesh bag in a cool, dry, dark spot.
Do not confuse spring crocus with autumn crocus. Autumn crocus (Colchicum) is a different plant that blooms in fall and is highly toxic. Check the label and buy from a reputable seller.
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Find My Plants →Planting the dish
- Pick a shallow container, 3 to 5 inches deep, with drainage holes. Bulb pans, low terracotta pots, and shallow bowls all work.
- Fill with light indoor potting mix to about an inch below the rim.
- Set corms pointed side up, close enough to almost touch. Crowding gives a fuller look and does not harm them during the short forcing period.
- Cover lightly so the tips just show or sit under a thin layer of mix.
- Water well and let it drain, then label the dish with the variety and the chill start date.
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Chilling the dish
- Chill at about 35 to 45°F in a refrigerator, cold frame, unheated garage, or cool basement that does not freeze hard.
- Keep the mix lightly moist, never soggy. Check every week or two and water when the surface feels dry.
- Keep away from ripening fruit, which gives off ethylene gas that can damage developing buds.
- Expect roots out the drainage holes and short shoots of 1 to 2 inches near the end of the chill. That is the sign the corms are ready.
Twelve to fifteen weeks is the usual range. Counting back from when you want flowers, add the chill time plus two to three weeks for bloom.
Bringing them into flower
Move the dish to a cool room, about 50 to 60°F, with indirect light for a few days so shoots green up. Then give it bright light, such as an east or south window. Cool temperatures keep stems short and blooms open longer, sometimes for a week or more. Warm rooms and direct afternoon sun make the flowers open and fade very quickly. Crocus flowers close at night and in dim light, then reopen in bright light, so a sunny window shows them best.
For more indoor bulb displays, see forced hyacinth jars, paperwhite narcissus forcing, and forced amaryllis.
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Forcing crocus in pebbles and water
Crocus can also be grown in a shallow dish of pebbles or in small crocus vases, with water just below the base of each corm. This works best after the corms have been chilled dry. Roots develop quickly once they reach the water, and the display looks clean on a table. Change the water weekly so it stays fresh.
After bloom
Forced crocus spend most of their energy indoors. You can keep the leaves growing in a bright spot, watering lightly until they yellow, and then plant the corms outdoors in fall. Some return in a year or two. For outdoor planting, see spring flowering bulbs to plant in fall and, if squirrels raid your bulbs, bulb cages for voles and squirrels.
Pet notes
Spring crocus can cause stomach upset such as vomiting and diarrhea in dogs and cats if eaten. Autumn crocus (Colchicum) is far more dangerous and can cause severe poisoning. Keep dishes where pets cannot reach them, and keep corms out of reach while you plant. If a pet eats any crocus, call your veterinarian or the ASPCA Animal Poison Control Center at (888) 426-4435 right away. See what to do if a dog eats a plant and what to do if a cat eats a plant.
Bottom line
Pack crocus corms shoulder to shoulder in a shallow dish, chill 12 to 15 weeks at 35 to 45°F with the mix lightly moist, then bring them into a cool bright room. Cool temperatures give the longest bloom, and spring crocus should never be confused with toxic autumn crocus.
Related reading
- Forced hyacinth jars
- Paperwhite narcissus indoor forcing
- Spring bulbs to plant in fall
- Pre-chilled bulbs for mild winter zones
- Forced bulb timing for indoor bloom
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