Blanching Cauliflower and Celery
This technique, called blanching, prevents sunlight from reaching these parts of the plant and turning them green. Unblanched vegetables are edible – but have a bitter flavor.
Cover the leaf stems of celery with soil or wrap them in paper or cardboard at least 10 days before harvest. Some gardeners use boards alongside the rows of plants.
Use the large leaves of the cauliflower plant for blanching. Start when the flower bud is less than 2 inches in diameter. Tie the outer leaves over the center of the plant with rubber bands or string. Check your plant often. The cauliflower head will be ready to pick in 7 to 12 days when it reaches 6 to 8 inches in diameter.
Many of the newer cauliflower varieties are self-blanching, eliminating this task. The upper leaves naturally fold over the center of the plant, blocking the sunlight.
A bit more information: Blanching is also the technique used for growing white asparagus. Soil or a container is placed over the young spears. The lack of sunlight interferes with cholorphyll (green pigment) production, resulting in white tender asparagus spears.