Gooday Niki,
Just a guess, you live in Melbourne?
I have had the same thing here. Caulies and Cabbages all ended up being
recycled due to bolting. I even had a Black Russian tomato plant which
was able to fruit after overwintering this year. I think that is amazing.
The hot days we had recently led to this I reckon.
The shade house could solve the problem if you can keep things watered
and allow some adequate light, what ever that is. I would make sure on
really hot days the sun is completely removed from plants, or only have
it in the early morning, keeping everything watered.
Here are some ideas on how to build it at home

http://www.heyne.com.au/gardencentre....php/Ferns.htm


http://www.gardenshedsgalore.com.au/shade.htm


http://www.ecoworld.com/home/articles2.cfm?tid=32



Niki wrote:
Hi there,
I have been having problems with most of my vegetables flowering even
before they reach a mature stage. Was wondering if that is due to the fact
that the weather has been so hot lately and the extended period of no
rain. Therefore, I decided to install a shadehouse to protect the plants.

a) Does anyone have any ideas on why the plants are all bolting?
b) Do you think the shade house will solve the problem?
c) How would you go about a home-made shadehouse?
d) What is the best material cover to use for the shade, what colour and
why?

TIA

Niki