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University of Minnesota Extension

Non-pest issues in cool-season crops

Quick facts

  • Cool-season vegetables include Brassicas (broccoli, cabbage, cauliflower), spinach and lettuce.
  • The ideal situation for cool-season vegetables is cool but moderate temperatures for the first month of growth.
  • Temperature deviations can cause issues that make these vegetables bitter or cause the crop to fail.
  • There are solutions to help get these crops through spring and ensure a good cool-season harvest.
Green lettuce plants in foreground that have elongated heads with flowers sprouting out the top. Purple cabbages are in the background on bare soil.
A bolting lettuce plant

Minnesotans love their cool-season vegetables, including Brassicas (broccoli, cabbage, cauliflower), spinach and lettuce. However, growing these crops in our climate can be a bit challenging. While fall conditions are optimal for most of these cool-season vegetables, Minnesota spring conditions are variable, and often lead to problems like bolting, lack of heads, and bitterness.

Ideal growing conditions for cool-season vegetables

Brassicas, lettuce and spinach all come from the Mediterranean region and surrounding areas, where winters are quite mild by Minnesota standards. They are biennial and winter annual crops, meaning that in their native habitat, they must go through a winter cooling period called vernalization before they can complete their life cycles and produce flowers.

In Minnesota, our spring weather is a lot like winter in the Mediterranean. So it can be tricky to get the right conditions for growing cool-season crops in the spring.

While each specific crop varies slightly, the ideal situation for cool-season vegetables is cool but moderate temperatures (50s and 60s) for the first month of growth. It’s warm enough that the plants are able to grow and put on plenty of leaves, and not quite cold enough to cause vernalization until the plants have accumulated substantial leafy biomass. At this point, once the plant has grown sufficiently large and experienced enough cold, it can shift into its reproductive phase.

Head or root forming vegetables like broccoli or radishes can begin to form their heads and roots at this phase. Ideally, this reproductive phase lasts a while so that the plants can develop large heads and roots before flowering.

Deviations from these weather conditions, though, can cause issues.

Bolting and other problems


Solutions to common problems with spring-planted cool-season vegetables


Author: Natalie Hoidal, Extension educator, local foods and vegetable production

Reviewed by Vince Fritz, Department of Horticultural Science, University of Minnesota


Reviewed in 2021

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