do you always water your trays etc before sowing cos i never quite know whether to do it before or after sowing
Yes! For seed, No for cuttings!
The reason I water first is the water sometimes washes the seed in to little clusters which is something I don't want, more so if I have meticulously laid them out individually.
Although I have not been asked why do I lay them out like this? it helps with pricking out and it helps to keep seedling roots tangling with each other.
Why do you mix some seeds with silver sand?
When sowing seed that are dust size you usually can't see if you have spread them evenly whereas you can see the sand.
Why do you put vermiculite on some seeds?
Some seeds require light to germinate and covering with vermiculite still allows light through.
Then you ask why cover?
You may never have noticed but when a surface sown seed germinates the tap root can lift the seed off the surface. The vermiculite is just heavy enough to hold the seed in place until it gets a hold in the compost, plus the vermiculite acts as an insulating blanket and keeps the seed just a bit warmer which in turn assists germination.
how do you know which seed to cover with compost/vemiculite and which do not?
Normally this information is on the seed packet! i.e. to cover or not to cover!
To add to the above information have a read of this page on my website;
http://tinyurl.com/yy5xkl