September Gardening Jobs

September is the final month of plenty in the allotment – there’s not much to plant, but harvesting and eating your produce will keep you busy! The sun is still warm and there’s time to enjoy the beautiful flowers that are still around before autumn really kicks in.

September marks the shift in the seasons from productive spring and summer to a slower pace in autumn. It’s a busy month, with plenty to harvest and lots of planting and other jobs to do for next year. I also like to take time to just sit in my garden, basking in the final warmth of the summer sun and watching the bees and other insects industriously buzzing around.

If your garden feels a little bare at this time of year, get some ideas for September flowers to brighten things up.

Flowers, shrubs & trees

What to plant in September

You may not see the fruits of your labours until next year, but by planting bulbs and seeds now, you’ll get to enjoy flowers early in spring. It’s also time to think about Christmas (no, really) – plant hyacinths and amaryllis this month to flower in December. Amaryllis 'Temptation' has festive red and white flowers that would look stunning as a centerpiece for Christmas dinner.

• Plant spring-flowering bulbs like daffodils, crocuses, bluebells and fritillaries in containers or in the ground. If you’re short of time, get daffodils in the ground first.

• Hardy summer-flowering bulbs like alliums, lilies and irises can also be planted now, before the weather cools significantly.

• There’s still time to plant colchicums, sternbergias, Crocus sativus and Cyclamen hederifolium for autumn flowers.

• Hardy annuals are easy to grow from seed and sowing them now means they’ll bloom earlier next year. Cornflowers, poppies, nigella, scabiosa and calendula can all be sown now for spring flowers. 

• Plant amaryllis bulbs and hyacinths in September to get flowers in time for Christmas. Find out how in our guide to growing your own Christmas flowers.

• The end of September is usually a good time to plant new perennials, as the ground is warm and moist. Heucheras are a great option for shady borders as their colourful leaves add interest throughout the year – Heuchera ‘Wild Rose’ is one of my favourites. 

• If you sowed biennials such as foxgloves, Sweet Williams and honesty in June and July, it’s now time to plant them out in their final growing positions.

• If you have a spare patch of land, turn it into a wildflower patch. Simply scatter wildflower seeds over prepared soil and protect them from birds with fleece or a deterrent such as shiny CDs or a fake bird of prey.

Propagating and dividing

Propagation is an economical way to grow your garden, but you do need to take cuttings at the right time. September is ideal for semi-ripe cuttings, which can be potted up and then planted out next year.

• Divide early-flowering perennials towards the end of the month, once the days start to cool off. Dig up the plant, use a spade or sharp knife to saw the clump into pot-sized pieces, soak them in water and replant immediately (or as soon as you can).

• You can propagate woody herbs (e.g., sage, rosemary and lavender), climbers, hedging plants (e.g., box) and evergreen shrubs by taking semi-ripe cuttings.

• Take cuttings of tender perennials such as penstemons, verbena, salvia, pelargoniums and heliotropes so you have a ready supply of new plants next year.

Harvesting, pruning and cutting back

• Harvest seeds from flowering plants to plant or store for next year. Once dried, seeds are best stored in labelled paper bags in an airtight container. Keep the seeds in a cool, dark place.

• Keep deadheading dahlias, roses and other flowering plants to extend flowering periods as much as possible.

• Continue to cut back perennials after flowering.

General maintenance

• Keep an eye on the forecast as nighttime temperatures begin to drop. You may need to close greenhouse vents and bring tender perennials inside if early frosts are forecast.

• Lift gladioli corms and store them in a cool, dry place over winter.

• Inspect leaves for notches left by vine weevil. You can remove beetles by hand, use sticky traps or apply nematodes to the soil – early September is the best time to do this.

• Watch out for powdery mildew and remove and destroy any affected leaves immediately.

Fruit and vegetables

What veg to plant in September

There isn’t much still to plant before winter, but it’s worth sowing green manure on any empty beds to protect the soil and add some nutrients back in next year.

• Seeds to plant in September for next year include broad beans, peas and spring onions.

• You can also plant hardy spinach and winter lettuce to harvest over the next few months, and you might just have time to squeeze in another batch of radishes!

• Plant autumn onions and shallots with the tips just poking out of the surface. They’ll be ready to harvest next summer

• It’s your last chance to plant potatoes for your Christmas dinner. Plant tubers in a grow bag in a cool conservatory or porch or a frost-free greenhouse.

• Sow green manure crops such as Italian ryegrass and crimson clover to capture nutrients from the soil. You can dig them in or cover the bed with cardboard in spring.

• Plant out any remaining strawberry plants, so they can get established before the winter

Harvesting

Most fruiting plants start slowing down in September, so if you’re feeling overwhelmed with produce just keep going for a few more weeks – you’ll be grateful for it in a few months when you’re still eating up the fruit and veg in the freezer.

• Autumn raspberries will be ready to eat this month, along with the last of the blackberries.

• Tomatoes may continue to ripen if it’s a sunny month, but you want to cut any unripe trusses before the weather gets too cold. You can ripen them indoors or make a batch of green tomato chutney.

• This is likely to be the last month to harvest beans, cucumbers, courgettes, peppers, aubergine and sweetcorn.

• Your first leeks and pumpkins may be ready to harvest this month.

• Lift and store any remaining maincrop potatoes. They should keep as long as they dry off before being stored in paper bags.

• Apples of all varieties will be ready to pick this month, as well as late-season pears and plums. Leave figs to ripen for as long as possible.

Fruit bushes and trees

• Prune blackberries and hybrid berries (e.g., tayberries, loganberries and boysenberries) after they’ve finished fruiting. Cut old canes and tie in new canes (the ones that didn’t fruit this year) to supports.

• Check apple and pear trees for canker. If you find any infected wood, remove and destroy it, then sterilize your tools.

General maintenance 

• Remove leaves from tomato plants, to give the fruits the best possible chance of ripening.

• Cut away leaves from around pumpkin and squash plants to let the sun ripen the squashes. Raise the fruit off the ground and keep feeding until you’re ready to harvest them.

• Cover brassicas with netting to stop the birds getting at them and keep a watchful eye for cabbage whiteflies.

• Cut bean and pea plants at ground level once they’ve finished producing, but leave the roots in the ground to decompose.

• Continue to protect carrot crops from carrot fly.

• Check tomatoes and potatoes for signs of blight – if you find any, deal with it immediately to save the crop.

Planning ahead

• Pre-order bare root fruit trees ready for planting in the winter.

• Pot up herbs like parsley, mint and chives and bring them indoors for the winter.

• Collect seeds from squashes, beans, tomatoes, peas and melons to dry and store for next year.

Lawns and hedges

Early autumn is the best time to plant a new lawn from seed, as it has plenty of time to get established before the winter. Growing from seed is more economical than turf and you can choose a seed mix to suit your soil and growing conditions.

• Prepare the ground for a new lawn a couple of weeks before sowing seed or laying turf. Remove any weeds, fork over the soil and level the surface.

• Reduce mowing of existing lawns and raise the blade height as grass growth begins to slow.

• Start autumn lawn maintenance – scarify using a rake or scarifying machine to remove dead thatch and spike the ground with a garden fork or other tool.

• Plant spring-flowering bulbs in lawns. Choose an area which won’t be heavily trodden and which can be left unmown until late spring.

• Give conifer hedges a light trim. Don’t prune leylandii now – that's a job for earlier in the growing season.

• September is a good time to plant evergreen and semi-evergreen hedges like box, yew, laurel and privet.

Other garden jobs for September

Autumn is the best time to carry out pond maintenance jobs as you’ll cause minimum disturbance to wildlife. Ponds rarely need (or benefit) from a deep clean, but you want to remove decomposing vegetation and sludge to keep nitrate levels low. In the rest of the garden, you can get ahead on the jobs that need doing to prepare your garden for winter.  

• Net ponds to prevent them from getting clogged by autumn leaves.

• Tidy up pond plants and remove any rotting leaves and excess vegetation, along with any blanketweed or duckweed.

• Remove some of the sludge and silt from the bottom of your pond – you don’t need to get rid of it all.

• Take advantage of good weather windows to clean out your cold frames and greenhouse ready for the winter.

• Clean out water butts or fit new butts to downpipes ready to collect rainwater.

• Set up new compost bins if necessary, ready to fill with old vegetation and autumn leaves.

FAQ

What to sow in September in the UK?

September is the ideal time to sow hardy annuals such as poppies, scabiosa, calendula, nigella and cornflowers, as well as wildflower seed mixes. Sowing in early autumn means they’ll flower in early spring. You can also sow winter lettuce, spinach and oriental leaves to harvest over the winter and early spring. 

What vegetables can I plant in September?

September is the best time to plant potatoes for Christmas. You’ll need to plant them in grow bags or buckets and keep them in a frost-free greenhouse or conservatory. You can also plant onions, shallots and garlic to harvest next summer and crops such as turnips and spring cabbages to grow over winter.

What flowers can I plant in September in the UK?

If you’re looking for autumn flowers, plant cyclamen, colchicums, and sternbergias. You can also plant Crocus sativus and harvest your own saffron. September is also the time to plant flowers for next year, including spring bulbs, biennials grown from seed (like Sweet William and foxgloves) and new perennials.

Can I plant leeks in September? 

Leeks take a long time to grow and need to be planted earlier in the year. You could try putting small leeks out in September but they’re unlikely to grow much. September is the first month you can harvest leeks if you started them out in February or early spring.