Do all greenhouses have to be heated?
I was planning on growing tomatoes, Aubergine, Sweet Peppers, Courgette and Sweet Potatos (do they go in greenhouse) in my greenhouse.
I also plan to grow outside: Blueberry's Strawberry's Leek, Carrots, Spring onions, Parsnip, Lettice and Swede.
Do I need to use a propogator for all seeds to start growing? And what does a propogator really do?
You only need to heat the greenhouse when there is an overnight frost or snow forecast to protect any plants in there such as seedlings, but you could just as easily start these off in the house and save on heating the greenhouse
The "plastic" window greenhouses are susceptible to high winds - as plastic is more flexible than glass, it is not uncommon for panes to get pushed out, so please do make sure it is located in a sheltered spot.
Your outdoor selection of fruit & veg looks fine. As regards sweet potatoes, ideally they are not an easy veg for newbies to try & grow, but there's nothing stopping you from trying - we all have to learn at some time. I can't help notice your location is west coast of Scotland - I'm wondering if you will have a long enough growing period for them or sustained warmth (hence, I understand the greenhouse question now)?
As regards to a propagator, these aid germination by retaining warmth and humidity and is suitable for most seeds. However, carrots & parsnips should be sown either directly outside when the soil temperature is warmer, or into something like cardboard loo inserts so that the roots are not disturbed (otherwise you'll end up with some interesting root shapes
). A heated propagator greatly helps germination of sweet peppers which need a much higher temperature for germination - be warned it can take up to a month before you see signs so don't be too discouraged.