Its a big subject to cover you need a book -- :o)
quickly--- plants aim is to reproduce and have found amazing ways of qetting their seed sown, trees for example want theirs spread around as planting too close would cause problems for them-- think of the 'helicopters' of the sycamore, also the shrubs such as hawthorn have a juicy red coated seed which goes through an animal to be distributed ( more difficult for us to do at home for trees and some shrubs, most need a period of cold so that they areready to germinate in the spring) some seeds remain dormant until conditions are right-- think of flanders poppies and the rosebay willowherb that needed soil disruption, and those which need fire --- mother natures wonderful

And just think of the wonders of fungus spores which will sit for years until they have the right conditions! Mushrooms would be absent from familiar places for so many years that when they finally reappeared people thought it was by some sort of process of spontaneous combustion :-)

You've answered your own question really, when you said "some need frosts" so clearly you already know that some need a cold spell, some need heat to grow. Bear in mind that the vast majority of plants we grow here in our gardens were never indiginous species, they were brought here from various parts of the world, where conditions vary hugely too. Which means the seeds will only grow under certain conditions, which vary from plant to plant.

thankyou everyone,,thats sort of helped,, it just seems that plants are such wonderfull things and just wish one could grow them all at once or at any time of year,,,
thankyou everyone xxx nice one

the old gardeners would say " Its the balance o' nature" if you look at what feeds on plants at different times of the year then everything -- including us -- rely on the plants, flowers birds and bees---- amazing