It may surprise some gardeners that brassicas such as cauliflower are biennial plants. This means that the plants’ lifespan is 2 years; they will grow the first year and bloom in their second year. Some brassica varieties will form a flower the same season they are planted because they have a vernalization temperature that is similar to the temperature of their growing season. Vernalization temperature is the point (after a certain amount of time) at which the plant “thinks” it has gone through a winter and begins flower initiation. In a cauliflower’s case the flower is its curd. Most spring and summer cauliflower varieties have a high vernalization, whereas fall, winter, and overwintering varieties have progressively lower vernalization points.
We experienced a great example of this at our trial grounds last week. After evaluating one particular cauliflower in our fall-planted field, we snuck down to our spring-planted field to steal some leeks for dinner (to evaluate their flavor, of course). Glancing over to the area where our spring-planted cauliflower were, we noticed one variety standing strong and producing some really beautiful, dense crowns! The rest of the plantings had succumbed to frost and time.
Imagine our surprise when we checked our database and found that we were looking at the same variety—one was planted in late summer for our fall trials, and the other had been set out in May for summer trials. This particular variety clearly has a low vernalization temperature, so the spring-planted crop had not initiated crown formation through the summer or fall. Both plantings were at the same developmental stage even though they had been started months apart.
Different varieties of flowering brassica crops such as broccoli, cauliflower, and cabbage have been bred for production in different seasons, so they have different vernalization temperatures. This is a great example of why we trial extensively to make sure that we can recommend the right variety for the right season.