Anyone used a hotbed for growing in winter?

I've not tried it but was tempted after watching Beechgrove, there's a clip here, hotbed is featured at around 24 seconds :-

BBC One - Beechgrove Garden, 2013, Episode 5, Sowing round carrots, progress in the hot bed and planting low-growing grasses

In that fine program, A Victorian Kitchen Garden, a few years ago they grew allsorts in hot beds. I might give it a whirl after the dreadful start to this years growing season.
Nowt to lose.

I can see the point of using one starting in January but would it be worth using one in say November time for starting off over wintering onions etc and winter lettuce. I noticed my big compost heap is red hot at the moment I could lob a frame on top and maybe utilise it

Your plants need light, not just warmth. The short dark days of winter aren't going to grow much at all

You know what it's like when your seedlings get leggy, due to too much heat and not enough light

yes good point thank you

I have thought about it to make the growing season longer the opposite end. I'd be likely to start it early in spring, when we have lots of light, but would need to make a cover as the frosts are bad.

So really perfect timing, as I'm about to go get a glass door today, and pick up some glass windows soon, and some old hay and make a 'sort of greenhouse' out of them. I could dig up and put some of that powdered manure from the horses winter feeding site in and then put the green house on top.

One problem that comes immediately to mind though, is how deep does the hole need to be, as you know we have rock fairly close to the surface. Some research will be needed I'd say.

Deep! You are ideally looking for 3 feet of FRESH manure! Not sure what your powdered stuff is. I've got a 2ft high raised bed which is waiting for me to barrow in loads of fresh horse muck. Inside the bed is dug down about 6inches, and then I'll mound it up a bit on top. Then on top of that will go basically a cold frame with 4inches of compost and earth at the bottom. That'll shrink as it composts.

'The Book' has details for different season extensions regarding depth. The Victorians topped their's up round the ride of the 'lights'

Although the victorians could manage pineapples (I guess they were just keeping them alive in the heat) and strawberries for Christmas.

Would my rather rubbish sweet potatoes this year have done better in a hotbox? I suspect its lack of heat rather than lack of light thats stopping them from flourishing for me... Need to pick your crop carefully I suspect...

Yip you can extend the end or start early or possibly get right through. Not sure I understand the over wintering onions... they are meant to go through winter aren't they?

Okay thanks. I'm thinking that I might make 9 inches into the ground max, but if I was able to put hay bales around all sides that would raise it again, but 3 feet! Still a small experiment would keep me busy.

From 'The Book' (Northern Hemisphere assumed)

"So, in general (provided it is about 60cm/ 2' deep), a bed made in mid-January will be warmed until the end of March; in mid- February it will be warmed until the end of April; and in mid-March until late May."
First, Jack (2013-01-10). Hot Beds: How to grow early crops using an age-old technique (Kindle Locations 613-615). UIT Cambridge Ltd.. Kindle Edition.

First also suggests digging a 6" deep hole and filling to 12" and treading it down to leave 12" above the soil level for small scale hotbedding.

He also has advice on drought affected areas. Not sure how that affects you down under, but effectively using a shallow hotbox (9") in the ground for fast growing crops and then taking the lid off for other things...

While he says you want 3ft depth, most of his book actually talks about 2ft! I could swear but can't find it, that he might have said 1ft per month of heat needed - So if you want to sow on 1st January and would need more frost protection than a cold frame alone can achieve on 1st March you need 2foot, 1st April 3foot etc. But if you design it with space round the sides of the growing frame you can top up too...

I cant see any reference to using bales as sides but that may just be because you loose a lot of growing space by having thick walls! Would imagine they will insulate it well! You need air to get in to do the composting process but not too much so that you keep the process over time.

Just debating when I will make mine -I have a risk of frist till Mid to Late May, but I think the cold frame can probably deal with that from about Mid-Late April. Probably looking at sometime in January filling it...?