Perlite, vermiculite, what's the difference?

As a new gardener, I'm a bit confused by all the products on offer. Could somebody please explain to me the difference between perlite and vermiculite. From reading the packets, they seem to do the same thing but I don't imagine that can be correct.

At the moment I am mixing my potting compost with perlite to make it lighter in texture and covering newly sewn seeds with vermiculite as it says on the seed packet to do this, but I don't know why.

Also, if I could please throw in one more question, almost all the seed pavkets say cover the newly sewn seeds with a plastic bag until they germinate, why is this? Is it for heat retention or moisture retention or both?

As my greenhouse is already 30 degrees in the day time ( I am in Turkey )should I be doing this?

Thank you, from a very novice gardener.

 

http://gardenerscorner.co.uk/forum/threads/grit-perlite-or-vermiculite.49152/
Thread above explains the difference, the bag is for moisture retention and heat, I would think your problem is providing enough shade.

 

Thank you. I see that there are lots of different opinions but I've got the drift. You are right about the shade . Have sunscreen netting as curtains on all 4 sides and across the top for shade which does prevent seedlings burning. This sort of stuff is very cheap here so can afford to be quite generous with it.

Didn't manage to successfully raise more than a quarter of the seeds I planted last year because of the extreme heat so this year I am being much more careful and shading everything. Don't yet know if I will do better this year but am gradually learning from past mistakes.

 

See also this recent thread:
http://gardenerscorner.co.uk/forum/threads/when-to-use-a-plastic-bag-for-seeds.50206/#post-653179

Yes and No!

Yes, because you need to retain humidity to help [most] seeds to germinate.

However, within a greenhouse that is already hot you risk that the temperature in the bags gets even hotter.

Google for the optimum temperature for germination and make sure you achieve that. If greenhouse is too hot you will need to germinate them in your house, and then as soon as they have germinated and have small shoots they can move to somewhere with better light; you need to do this promptly after germination because if they are left in poor light the new seedlings will grow tall and weak (so called "leggy"). A greenhouse, with some shade if it is hot & sunny so they don't wilt!, should be fine once germinated.

High temperatures can induce dormancy in [some] seeds and prevent it from germinating (because it will think it is mid-Summer rather than Spring when it wants to germinate, normally)

 

Thank you Kristen. Your reply anout dormancy has helped me understand whats goingbon withnmy seeds. Seeing seeds is particularly challenging here because spring comes so early, already all the geraniums and osteopermums are in full bloom - but nothing happens at all between early June and September when temperatures climb to the 40's and there is zero rainfall for 3 months.

In October, we have a second spring and everything which has been totally dormant during the summer bursts into bloom again.

I think that I need to sew my seeds at least a month before the suggested date given on the packet.

Although the greenhouse is not heated, the temperature rarely drops below 12 degrees in the winter and by February, it's usually around 18.