Cabbages are cool season crops that best suit a maritime climate with mild temperatures. While cabbages will grow at temperatures above 7°C (45°F), they grow best at 15- 18°C (59-64°F). As temperatures increase cabbages are more prone to tip burn. Above 27°C (81°F), plants may bolt, causing the heads to split open. They have moderately high frost tolerance.
Most common practice is to transplant greenhouse raised plugs into the field. Cabbages need a constant water supply and good soil aeration. On light soils, in anything other than temperate climates, irrigation is needed. Lack of water leads to poor development of outer leaves combined with small firm heads and a stronger taste.
Irrigation after a period of drought can lead to a splitting of cabbage heads, due to a rapid increase in growth. Early cabbage varieties suit locations with an early start of vegetative growth and low risk of early season frost.
Autumn & storage cabbages suit heavy, deep soils and milder temperatures (maritime climates).
Cauliflowers are also a cool-season maritime crop with distinct temperature requirements for producing the best curds. Minimum mean day temperatures for winter cauliflowers need to be above 4°C (39°F) and before curd development starts, short frost periods up to - 10°C (14°F) are tolerated. Optimum daytime temperatures are 18- 20°C (64-68°F).
Leaf production has to be optimum to sufficiently cover and protect the curd, maintaining a good white blanched nature.
Broccoli is a hardy, cool season brassica, which will germinate and grow in temperatures from 4 to 35°C (39-95°F). Optimum temperatures though are 16- 18°C (61-64°F). Although a cool season vegetable, production occurs in hotter climates. Here correct choice of variety is critical.
Irrigation and good soil moisture control is necessary and extreme temperatures can lead to accelerated growth and hollow stem.
Brussels sprouts are a cool-season crop and grow best when daytime temperatures average about 18°C (64°F) or less.
The best quality brussels sprouts are produced in good autumn or winter sunlight conditions, because high temperatures result in poor quality produce and increase puffiness or looseness in the harvested button. Sprouts can withstand heavy frost. They are often planted for harvest in the winter when sprouts have a tighter button and a milder flavor.
Leafy brassicas have a 4-5 week growing cycle and need a good nitrogen:potassium balance for productive growth. As many as 7-9 crops can be achieved every year through regular cutting of low growing crops. They grow best in cool, moist environments, but are more commonly found in higher temperature, fast-cropping situations.
Bolting due to cold temperatures can be a problem in crops planted too early in spring in cooler climates.