The Flowers That Bloom on My Onions

The vegetable crops we grow have specific parts that are edible. For example, we grow tomato, cucumber, eggplant, etc. for their fruit. For these plants to produce fruits, they have to produce flowers. Those flowers must then be pollinated. Pollination brings together two sets of chromosomes, which results in viable seeds which can be planted next year to continue the species. Pollination also causes the ovaries which contain these seeds to swell in size. These swollen make up the fruits – the tomatoes, cucumbers, eggplant, etc. – that we consume as fruits and vegetables.

Meanwhile, we grow other vegetable crops not for their fruits, but for other edible plant parts. Onions, for example, are grown for their fleshy bulbs (which are actually modified leaf tissue). We grow carrots and parsnips for their roots, and we grow greens such as lettuce, spinach, kale, etc. for their leaves. We do not want flowers on these plants. If one of these plants produces a flower, the edible quality of those plants is reduced, since the plant will then put all of its energy into the flower and less into the leaves, stems, and other edible parts.

Under certain conditions, plants such as onions, carrots and greens will produce a flower. This can arise due to cold temperatures (onions) or hot temperatures (lettuce, spinach, and other greens). The unwanted production of a flower is known as bolting.


So how do we prevent bolting? For greens, bolting can be prevented by planting and harvesting them during the cool weather seasons. Lettuce and spinach grown in hot weather have a greater chance of bolting than does spring or fall-planted spinach.

Onion flowering can occur at low temperatures, a process called vernalization. This can happen when planting onion sets that have been stored at temperatures of 40-50oF for two or more weeks are planted right away. To prevent vernalization, expose them to 80oF temperatures for 2-3 weeks, or make sure to plant them early in the spring. To further reduce the chances of growing flowers instead of bulbs, plant onion sets that are half an inch in diameter. These smaller sized sets lack the necessary food reserves for flower production. Larger sized sets have a greater quantity of stored food and are more subject to vernalization. These, however, can be grown for green onions.

Carrots are biennials. They will produce stem, leaves and taproot the first year. If left in the ground over the winter, the following spring, they will produce a flower similar to that of a Queen Anne’s lace. Usually we never see flowers on our carrots because we harvest the roots the first year. However, if you leave carrots in the ground to overwinter, make sure you dig them up before they start to sprout, otherwise, if allowed to flower, the roots will not taste good.


Flowers are beautiful and necessary, but only on certain garden plants. If you want your greens, bulbs, and root crops to be tasty, then don’t let them flower.

Leave a Reply

Fill in your details below or click an icon to log in: Logo

You are commenting using your account. Log Out /  Change )

Twitter picture

You are commenting using your Twitter account. Log Out /  Change )

Facebook photo

You are commenting using your Facebook account. Log Out /  Change )

Connecting to %s