If it has been a good growing season, some of the more vigorous hedges might be in need of a final light clipping; really just a tidying up. Never make this severe or you could end up with bare patches through the winter.
September is a good time of year for planting evergreens and conifers. Because the ground still warm after the summer, but also quite moist, which encourages early root growth and, therefore, quick establishment.
Prepare the ground by incorporating well-rotted garden compost, manure or humus, etc, and plant firmly. Trees and taller shrubs will need good support against autumn gales. To provide support, drive a stake in to the windward side and use a propriety tree tie to secure. Smaller trees and shrubs at can usually be adequately supported using a stout cane or two.
September is also the best month to plant out any trees, shrubs or herbaceous plants that you have been raising from seed.
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Deciduous trees and shrubs in flower:
Buddleia (butterfly bush)
Cotinus (smoke bush)
Fuchsia (many cultivars)