Blanching cauliflower doesn't make it taste any better, but the snow-white curds of a blanched head are more appetizing than the green, yellow or brown curds you will harvest from an unblanched head.
The heads are ready to blanch when they are about two inches across. Choose a warm, sunny afternoon to work with your plants, and make sure that they are totally dry before you can begin, because working with wet plants encourages disease and rot. The only supplies you will need are some soft twine or rubber bands.
To blanch the head, pull some of the leaves from the sides of the plant up over the head and secure them with twine or rubber bands. Cover the head enough to completely shade it from light and protect it from moisture, but leave openings for air to circulate. Self-blanching cauliflower types such as Fremont or Ravella have leaves that naturally curl up over the head.
Once you begin blanching, never water your plants from the top. Use a soaker hose or other system to soak the roots, but leave the head and leaves as dry as possible. Unwrap the heads after a hard rain to allow them to dry out, and check them for insects from time to time. They grow quickly at this stage, and will probably be ready for harvest in a week or two.