[cranberry]

Hi, New to this veg growing and could do with a bit of guidance please. I have dug over bed where i am going to plant carrots, read that i should cover now to warm soil, what temp should it be? then 2 weeks before planting use a sprinkling of bone meal. I would also like to plant parsnip and beetroot in same bed, is bone meal ok for them?

[Trillium]

Bonemeal is good for all plants as it's really a soil feeder from which the plants draw nutrients. But bonemeal needs close to 4 months to break down enough to be useable so what you throw down now will be absorbed by plants in the late summer/early fall. So its best to throw some down at the end of fall and some in early spring to catch the main growing periods.
Not sure where your area is, but it seems a bit early to be sowing carrots. They don't like cold at all when young and even though you'd cover the soil to warm it, you'd need to keep it warm while the carrots sprout and grow until the weather is warm enough to continue the growth.
Parsnip in the same bed is iffy; the mature leaves get so large that it would either swamp or shade carrots which need sun, so parsnips should go at the north end of a bed. Beet tops can get a bit large too so you'd not want to crowd them close to carrots either. 'Proper Rotation' says not to manure any of these crops, but I always fling loads of manure every year and get very tasty crops with minimal forking of parsnips and carrots.

[Stripey_cat]

One old guy I know says it's warm enough to sow when you can drop your trousers and sit down comfortably on the soil!  I'm not sure how well this would work on a public allotment site....  Testing with a bare elbow (like baby's bath water) might be a safe compromise.

[cranberry]

Thanks for all the advise guys, all taken on board.