These early and substantial harvests are before the arrival of brassica caterpillars, and finish in time to plant a second vegetable. Tips include to raise plug plants, use fleece/row cover and be #nodig for less slugs, fewer weeds and warmer soil.In this climate zone (8b mild, temperate) you can also sow brassicas in early summer for cropping in autumn, see https://www.youtube.com/watch?v=xWxtKTNlgbM
This sowing timeline on my website gives best dates for vegetables all year https://www.charlesdowding.co.uk/learn/sowing-timeline-vegetables/
Filmed and edited February to July 2017 by Edward Dowding