Hi Diane,

Thanks for submitting your question to Ask Extension. Allium are tricky to force indoors but it can be done. 10-15 weeks of cold treatment (vernalization) at 32-42 degrees F are required to simulate winter. 12-15 weeks of cold result in better blooms. Unlike daffodils or tulips, ornamental onions need a longer and colder exposure to chilly temperatures followed by a long exposure to bright light to grow their best in an indoor environment. If these conditions aren’t met, the bulbs may only produce leaves or any flower stalk that does grow may be weak and topple once the flower head forms. After chilling move to a bright cool spot (60-65 degrees F) to encourage green shoots. You may need to provide supplemental light.

To begin, fill containers with a well drained potting mix leaving about one inch of soil above the bulb’s tips. Taller varieties like gladiator may require staking. Water the container thoroughly, allowing the water to drain out. Keep the soil evenly moist but not soggy. Then do your cold and dark treatment, preferably 10-12 weeks as mentioned above. After the initial cold treatment, relocate the containers to a brighter area and continue the cold treatment for another three weeks. Once the white shoots start coming up provide as much sun and supplemental light as possible.

Here is a link to a good article about forcing alliums. How To Force Allium Bulbs

Forcing Bulbs – Wisconsin Horticulture