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Gardening in Italy?→ September’s almanac for the Italian climate
ALMANAC · UK CLIMATE

The garden in September

September is one of the best months of the gardening year. The soil is still warm and moisture returns, which makes it ideal for planting: roots grow through autumn and plants start spring already established.

Nights are cooling, though, and tender plants need a plan. Most can stay out until the end of the month in the south, but the first frost can arrive in cold gardens before October.

UK and similar cool temperate climates. In the north and in frost pockets, bring tender plants in early in the month.

AT A GLANCE

Spotlight: bringing tender plants indoors

The right moment depends on the plant's minimum, not the date. Tropical plants that summered outside — Chinese hibiscus, gardenia, gerbera, crotons, warm-growing orchids — should come in once nights fall below about 10°C. Tougher Mediterranean plants such as bougainvillea, oleander, plumbago and cymbidium orchids can stay out until just before the first frost; cymbidiums actually need the cool nights to set their flower spikes.

Before bringing anything in, check it carefully: aphids, whitefly, scale insects and mealybugs that are controlled by predators outdoors multiply fast in a warm room. Wash the leaves, remove fallen leaves from the compost surface, and isolate anything suspicious for a couple of weeks.

Indoors, give plants the brightest spot you have — light, not warmth, is what they lack in winter. Most will drop some leaves as they adjust. Cut watering right back: a plant that barely grows through winter uses far less water than it did outside in August.

HibiscusGardeniaGerberaBougainvilleaOleanderCymbidium Moving plants indoors/outdoors seasonally ›

Jobs this month

Autumn planting

Warm soil and cooler air are perfect for new plants. Anything planted now needs far less watering than the same plant put in during spring.

Plant daffodils, crocus and muscari; wait until October for tulips. DaffodilCrocusGrape hyacinth
Plant or divide perennials such as heuchera, bergenia and rudbeckia. Propagation: division › HeucheraBergeniaRudbeckia
Plant evergreen shrubs: pittosporum, fatsia, nandina, escallonia. PittosporumFatsiaHeavenly bambooEscallonia
Sow sweet peas in deep pots to overwinter in a cold frame at the end of the month. Propagation: sowing seed › Sweet pea

Bringing plants in

Tender plants that spent summer outside need to come in before nights drop below their minimum. Check them for pests first, and give them the lightest spot you have.

Bring hibiscus, gardenias, gerberas and dendrobiums in before nights drop below 10°C. Moving plants indoors/outdoors seasonally › HibiscusGardeniaGerberaDendrobium
Bring cymbidiums in before the first frost, into a bright, cool room. Moving plants indoors/outdoors seasonally › Cymbidium
Move yuccas and ponytail palms back inside. Moving plants indoors/outdoors seasonally › YuccaPonytail palm
Check under leaves for aphids, scale and mealybug before plants come in.

Kitchen garden

Main-crop harvests continue. Cleared beds can be sown with green manure or covered to protect the soil over winter.

Harvest main-crop potatoes, apples and pears. TomatoCrab applePear
Plant overwintering onion sets and garlic late in the month. Ornamental allium
Sow green manure on empty beds.
Pick the last cucumbers and remove plants once they fade. Cucumber

Lawn care

Autumn is the best time to repair lawns: warm soil and regular rain help grass seed establish before winter.

Scarify and aerate lawns, then overseed thin patches. Lawn basics ›
Raise the mower blades as growth slows. Lawn basics ›

Sow and plant

Sow
  • Sweet peas (in pots, for overwintering)
  • Hardy annuals in mild areas
  • Green manures
  • Winter salads under cover
Plant out
  • Spring bulbs except tulips
  • Perennials and evergreen shrubs
  • Overwintering onions and garlic
  • Spring bedding: wallflowers, violas

Watch out for

Early frostClear, still nights late in the month can bring the first ground frost in cold gardens.Grey mouldDamp, cooler weather spreads botrytis on dahlias, fuchsias and late flowers.Honey fungusClumps of honey-coloured toadstools at the base of dying trees or shrubs appear in autumn.

Questions

When should I plant daffodils?

September and early October, around three times their own depth. Tulips are planted later, in October or November, which reduces tulip fire.

When do I bring plants indoors?

Before nights fall below the plant's minimum: around 10°C for tropical plants like hibiscus and gardenia, just before the first frost for tougher ones like cymbidiums, bougainvillea and oleander.

Is autumn a good time to plant?

One of the best. Soil is warm, rain is regular and plants root before winter, so they need less water next summer.