Early autumn is the most productive few weeks in the gardening year. The soil is still warm, there's usually moisture about, and almost everything you plant now establishes roots before winter and races away in spring.
Here's what's worth doing between now and the first frost — roughly mid-September to late October in most of the UK.
Divide overcrowded perennials
Clumps of hardy perennials — hostas, daylilies, geraniums, asters, ornamental grasses, rudbeckia — lose vigour and flower less once they've been in place three or four years.
- Lift the whole clump with a fork.
- Split it into fist-sized pieces, keeping healthy roots and shoots on each. Use two forks back to back, a spade, or an old bread knife for tough crowns.
- Discard the tired, woody centre. Replant the vigorous outer sections at the same depth, water in well.
You get free plants and stronger flowering next summer.
Plant spring bulbs
Get these in while the soil is workable:
- Now to end of September: daffodils, crocus, snowdrops, alliums.
- October into November: tulips — planting them later reduces the risk of the fungal disease tulip fire.
Plant at roughly three times the bulb's own depth, pointy end up, in free-draining soil. In heavy clay, sit each bulb on a handful of grit. Plant in generous groups, not single lines, for the best display.
Sow hardy annuals and sweet peas
Hardy annuals sown now — calendula, cornflower, larkspur, poppies, ammi — overwinter as small plants and flower weeks earlier and bigger than spring-sown ones. Sweet peas sown into deep pots now and kept in a cold frame or unheated greenhouse build strong roots for an early, vigorous display.
Lift and protect tender plants before frost
Frost will kill these, so act before the first one:
- Dahlias, begonias, cannas, gladioli: once frost blackens the foliage, lift the tubers or corms, dry them off, and store somewhere frost-free in dry compost or sand.
- Pelargoniums ("geraniums"), fuchsias, salvias: bring pots into a frost-free porch, greenhouse or bright windowsill, or take cuttings now as insurance.
- Borderline-hardy plants staying outside (tree ferns, bananas, agapanthus in pots): mulch the crown thickly, wrap with fleece or move pots against a house wall.
Tidy selectively — not everything
- Cut back collapsed, slimy or mildewed growth, and anything diseased (bin it, don't compost).
- Leave standing seedheads and hollow stems on grasses, sedums, echinacea and teasel. They look good through winter and shelter ladybirds, lacewings and other beneficial insects. Cut them in late winter instead.
- Rake fallen leaves off the lawn and out of pond and border crowns, but pile them somewhere to rot down into leafmould — the best free soil improver there is.
Look after the soil
Spread a 5cm mulch of compost or well-rotted manure over bare soil and around perennials and shrubs. Worms work it in over winter, it protects soil structure from heavy rain, and it suppresses weeds. Don't dig it in — let the soil do that.
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