Purple sprouting broccoli
 

This is my first year growing broccoli and I have no idea when or how to harvest it! Purple spears have appeared at the top and sides of most of the plants - what do I do next?
Also, I have had some garlic in a bed since October - one type said harvest in Spring and the other in Autumn. The spring variety has started to yellow on the leaves - does this mean that it is ready to be harvested?
Thanks in advance guys - this forum is a million times better than any gardening book that I own!