Q.Cauliflower Plants Have Long Straggly Stems, Should I Plant Them Deep.
I bought some cauliflower plants and the stems are approximately about 6″ long before the first leaf. should I plant them deep in the ground.

Certified GKH Gardening Expert
It sounds like a lack of light has made them stretch. That, or cramped container space.
It is not advised to plant them much deeper than the crown. This can cause rot, and the loss of the plants.
Here is an article that will help you to grow them:
https://www.gardeningknowhow.com/edible/vegetables/cauliflower/growing-cauliflower.htm