In September the soil is still warm and rain returns, which makes it a month for harvesting fruit and maincrop vegetables and for planting bulbs, perennials and shrubs.
It is also the main month for lawn repairs, for taking cuttings of tender plants and for bringing them under cover before the first frost.
September is the hinge of the gardening year in Britain and northern Europe. The soil is still warm, rain usually returns after summer, and the first frosts are weeks away in the south but possible before the end of the month in the north and on high ground. It is a month for harvesting, and one of the best for planting.
Warm, moist soil makes early autumn the best time to plant hardy perennials, shrubs and container-grown trees, which root through the winter and need less watering the following summer.
Daffodils, crocuses, alliums and most other spring bulbs are planted in September, at about three times their own depth. Tulips are left until November, which reduces the risk of disease. Hardy annuals such as cornflowers, pot marigolds and love-in-a-mist, sown in the open ground, flower earlier the next year than spring sowings.
In the vegetable plot, winter salads, spinach and spring cabbages go in, and overwintering onion sets and garlic follow from late September. Empty beds are sown with a green manure, such as grazing rye or field beans, or covered with a mulch of compost.
September is the main month for lawn work: raking out moss and dead grass, spiking compacted areas, applying an autumn feed, and sowing seed on bare patches or new lawns. The mower blades are raised as growth slows. Details are given under looking after a lawn.
Deadheading dahlias, roses and late perennials keeps them flowering until the frosts. Overgrown clumps of perennials that flowered earlier in the year can be lifted and divided. Seed is collected on a dry day from plants worth multiplying.
Cuttings of tender perennials such as pelargoniums, fuchsias and salvias, taken early in the month, root quickly and are an insurance against losing the parent plants in winter. Seed heads and hollow stems left standing give shelter to insects and food to birds; the borders do not need cutting down in autumn.
Fertilisers high in nitrogen are not applied to trees, shrubs or perennials after late summer, since the soft growth they produce does not ripen before winter. Evergreen hedges are given their final trim early in the month. New hedges, fruit trees and roses can be ordered as bare-root plants for delivery from November.
Shading is removed from greenhouse glass as the light weakens, and watering and feeding are reduced. Tender plants that have spent the summer outdoors, including citrus, pelargoniums and tender succulents, are brought under cover before the first frost.
A net is stretched over ponds before the leaves fall. Hedges can be cut once the nesting season has ended, and nest boxes are cleaned out. Ivy is left to flower, since it is a major late source of nectar. Bonfire heaps are checked for hedgehogs before lighting, or built on the day they are burned.
Under the guidance issued by the RSPB in 2026, seed and peanut feeders stay empty until the end of October; the reasons are set out under gardening for wildlife.
Clearing spent crops and bedding produces a large volume of material for the compost heap, which is best mixed with shredded prunings or cardboard. Fallen leaves are kept apart and made into leaf mould.