Autumn is a great time of year for collecting seed, and sowing it. Many tree and shrub species can be sown in autumn, in fact they need a winter chilling before they can feminists in Spring. This requirement for cold exposure is called cold stratification.
Leave trays of sown seeds in a sheltered spot outdoors over the winter.
Watch out for signs of germination in Spring and then bring them into the green house.
A covering of horticultural grit will help to reduce the growth of miss in the surface of the compost.
Ciaran The Gardener 