February 26, 2018 | Drew Habig, Horticulturist

Things keep moving at the greenhouses at Chatfield Farms. This month at the greenhouse we sowed onions seeds for the Community Supporting Agriculture (CSA) farm and market garden. 16,500 seeds of onions and their near relatives were sown in one week! We sowed eight varieties of onion, three varieties of leek and one variety of shallot. It was a busy few days planting some pretty small seeds. The onions will be distributed to members of the CSA farm that Denver Botanic Gardens manages, as well as being sold at farmer's markets in areas where fresh produce is difficult to find nearby.

Onions are hugely important in the food we eat. While they’re not the most glamorous vegetable, they’re my favorite to cook with because of how they are used in many different dishes. From the base of so many soups and chilis, to slow cooked sweet caramelized onion dip, to crisp and bright macerated onions in tacos, the great Allium cepa is in a lot of what we eat. Its large culinary profile is matched by a large profile in the growing season. We sow the seeds in early February for a harvest in late summer. That’s about six months of growing to make an onion! Luckily they store really well over the winter which is why we sow so much seed now.

The reason for the long growing season is because the onions first need to grow their foliage before long summer day lengths trigger them to begin storing sugars in their underground bulbs. If they haven’t grown large enough before then, the bulbs produced will be small. Seeds get sown in early February and grow inside until mid-April, when they’re planted outside. The cold tolerant seedlings survive outside and grow only foliage until long daylengths in June trigger them to begin forming their large bulbs. They are harvested in late summer and brought back to the greenhouse to dry and cure, which increases their storage life. The greenhouses smell amazing in the fall.

If you’re looking for more information on growing your own onions, here is a great CSU extension article.

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