The late-summer garden is all about planting perennials, collecting seeds and ordering bulbs – and there are still lots of blooms to enjoy, too.
In September, the garden starts the seasonal colour shift to sunset shades of yellow and gold, with ornamental grasses and late summer flowers like helenium, rudbeckia and chrysanthemums taking centre stage in the landscape.
It’s the season of abundance and a time to make the most of the garden in the warm September sun before cooler weather arrives.
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Hopefully you’ll still be reaping the rewards of long months of sowing and growing. In the vegetable garden it’s time to pick those plump squashes and the last of the summer tomatoes, courgettes, sweetcorn and beans, as well as harvest apples, plums and pears. It’s also important to keep an eye on brassica plants and make sure cabbages, kale and broccoli are netted to deter cabbage white butterflies and pigeons from nibbling them.
This month is also about looking ahead and preparing for the growing season to come, tidying the garden and getting plants in shape.
It’s the best time to neaten up hedges and give evergreen shrubs like laurel, bay and privet a light trim to get the structure of your garden shipshape. Plants like these tend to be the main interest over the winter months when everything else dies back, so need to look their best.
Flowers to grow in September
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September is a busy month in the flower garden, with plenty of jobs to be getting on with.
“The dahlias have been putting on a beautiful display and will continue their abundance throughout September,” says flower farmer Lowri Johnston of Blodau Caredig in Carmarthenshire. “I’ll also be cutting sunflowers, zinnias, cosmos and calendula, as well as drying the last of the strawflowers and statice. It’s been a fabulous year for drying and it’s great to have rows of dried flowers ready for autumn.”
Propagation for next season is also well underway by September, with lots of hardy annuals being sown including Ammi majus, Scabosia, cornflowers and snapdragons. “Many of the hardy annuals can be started now for earlier flowers next year, with a second batch being sown in the spring, for continuous flowers during the summer season,” says Lowri.
September is also a good time to split perennials. Lift and divide perennials that have outgrown their space. This will refresh the plant and creating new clumps to spread or gift.
“This year I’ll split some perennial grasses, Geum and Echinops, as they have been established a few years and it’s a great way of getting new plants,” says Lowri. “I’ll also be starting lots of new perennials as I’m expanding my perennials patch and now is a great time to do this. Achillea ‘The Pearl’ has been really useful as a filler flower this year, so I’ll be planting lots more of that.”
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In September, Lowri collects sweet pea seeds and also direct sows Nigella seeds straight from their dried pods. “Collect sweet pea seeds by letting them dry on the vine, before opening the dried pods, tipping out the seeds and drying them on kitchen paper in the house for a few days before storing them in a cool dark place. Meanwhile Nigella are always best sown direct in the ground.”
Make sure you have Ranunculus and anemone corms ready to start in October – and that your spring bulb orders have all been done, as it will soon be time to plant them.
“Cosmos and dahlias are in their full glory,” agrees flower grower Julie Woodford of Madge & Ivy in Berkhamsted. “Keep picking these cheerful stems to prolong flowering. As the month progresses, note which dahlia tubers you’d like to lift once the frosts arrive, ready to divide and increase stocks of your favourites for next year.”
Julie began growing violas and pansies for the first time this year and has completely fallen for the antique, peach and mulberry varieties. “When planted closely, they produce longer stems for cutting that last well in a vase. They thrive in partial shade, and by collecting seed throughout the summer, they truly are flowers that give and give. September is the perfect time to sow viola and pansy seeds under cover or take cuttings to ensure cheerful winter flowers as they are surprisingly hardy little plants.”
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Now is also the time to plan and plant spring bulbs, rewarding you with flowers just as the garden reawakens. September is ideal for planting swathes of narcissi, alliums and muscari, while tulips prefer to be planted in colder ground later on in the year.
This is also the perfect moment to take semi-ripe cuttings of lavender, hydrangeas, and herbs such as rosemary. “Cut just beneath a leaf node, strip off excess foliage, and place cuttings around the edge of a pot filled with peat-free compost,” advises Julie. “Water well, keep out of direct sun, and in 2–3 months roots should appear, ready for potting on.”
Vegetables to grow in September
“While we’re past the peak of the growing season, September still offers plenty of meaningful jobs for the productive garden,” says Penny Hemming, head gardener at the Riverford Field Kitchen in Devon.
“There’s just about time for a final sowing up of winter radish. You can do this until the end of September. These hardy roots mature quickly and bring a satisfying crunch to autumn salads.”
Now is a great time to sow oriental leaves too. “Hardy greens like pak choi, mustards, mizuna, and tatsoi thrive in cooler weather and can be harvested through winter,” says Penny. “Sow several seeds in each module to bring on then plant out in their final position. If you have a polytunnel or greenhouse, you can continue growing nutritious leafy greens like land cress, winter purslane and winter salad mixes right through the colder months.”
Penny also recommends planting raspberry bushes now, choosing a mix of early, mid and late varieties. Now’s the time to take runners from this year’s strawberry plants too and pot them up so you have more plants ready for next season.
Garden jobs for SeptemberTidy up flower beds
Keep deadheading to extend flowering and prevent plants putting energy into seed. Clear fading annuals and add them to the compost heap, enriching soil for next season.
“But don’t be too tidy,” says Penny Hemming. “In ornamental beds, leave stems and seed heads standing through winter. They might look a bit scruffy, but they’re a haven for insects. Frost sits beautifully on seed heads, and their hollow stems offer vital shelter to insects. So only cut back where needed.”
Start composting
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If you don’t already compost garden waste now is a great time to start as September’s cutbacks make great compost material. Establish a compost bin and add prunings, leaves and grass clippings. Cover to keep the rain out and the compost warm. “Come spring, you’ll be able to spread three inches of homemade compost over your beds to get them off to a flying start,” says Penny.
Store fruit correctly
“It’s time to harvest and store any apples or pears from trees in your garden,” says biodynamic farmer Jane Scotter, who runs the How To Grow Exceptional Produce course with Create Academy. “This year has been a very abundant top fruit year, so many of us will have an excess. Store in a vermin-proof space that is dark, cool and dry – such as a garage or outdoor shed.”
Enrich the soil
It is time also to start bedding down your garden for winter. “Start by tidying brown, spent stems and giving the soil one last weed,” says Jane Scotter.
“Add a generous top dressing of rich compost over the next couple of months to provide good ground protection over winter and enrich the soil, thus ensuring beautiful, healthy growth next spring and summer.”
Mulch any bare soil with compost to prevent erosion, suppress weeds, retain moisture and feed the soil through winter. Rake fallen leaves and store in netted bags to create nutrient-rich leaf mould that can also be used as mulch once it has rotted down.
Take houseplants back indoors
If you moved houseplants outside for a summer break, it’s time to move them back indoors. Check plants over carefully to make sure you’re not bringing any pests inside and cut off any faded leaves.
Use harvested rainwater from the water barrel to keep them hydrated through the cooler months of the year. It’s fine to reduce the watering frequency now too, as your houseplants will need less through the autumn and winter months.
Clean ponds and water features
Late summer is a good time to freshen up your pond. Check for any build-up of plant debris as this can lead to problems with algae and blanket weed if ignored. Scoop out any floating leaves and cover your pond with netting to keep autumn foliage from trees and shrubs at bay.
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