Posted: 06/09/2013 at 09:19
The general wisdom is that autumn planting allows plants to establish a good root system over winter because in autumn the soil is warm enough and moist enough to encurage this and, with most plants going dormant above gorund, there isn't a lot happening to stress the roots as they grow.
Plants that get established in autumn and over winter do not usually need any watering in teh new season. Spring planted plants have to cope with establishing roots while supporting a spurt of energy and growth above ground so can get stressed and will require careful monitoring for watering and feeding.
However, in my own garden I have learned to plant all except the hardiest shrubs and trees in spring as I can lose new plants to hard winters. Normal British winters should be OK unless you're in a very exposed area. If you're worried about marginally hardy plants, pot them on into bigger pots and keep them under frost free shelter for winter then plant out in spring.