In autumn soil temperatures are still warm enough to encourage root establishment and growth, but not too warm as to stress new plants. Planting in spring risks high temperatures before the plant has had time to establish itself.
As the soil temperature and climate are cooler in autumn, the soil takes longer to dry out after watering meaning. This means it takes less water overall to establish the plant.
Slower Weed Growth
Weeds tend to appear and thrive more so in the warmer months. This year particularly has seen an abundance of weeds due to the temperature and rainfall. Planting when weeds are less active gives your plants an opportunity to become established before having to compete with weeds.