What to Do in the Garden in September
Living North's gardening expert Ross Pearson shares his advice on what needs to be done in the garden this month
The garden responds in kind. Colour shifts subtly, foliage begins to thicken, and the tempo of everything seems to settle. This is no longer the showy season. Nothing is desperately clamouring for your attention. Instead, it offers a different kind of satisfaction, the sort that comes from taking stock, making space, and preparing soil for what’s to come. Seed heads appear where flowers once were, stems lean a little more, and foliage looks a bit, well, knackered.
It is also the time for us gardeners to take a breath. Not to stop, because there is still plenty to be done, but to observe things more closely. To notice what worked well, where the gaps are, which combinations sang, and which were simply rubbish. There is time now to think without the urgency of spring or the height of summer distracting the eye. You’ve seen what worked and what didn’t, which plants earned their keep, and which ones coasted through on looks alone. There’s time to think before acting, which always feels very grown-up in a garden. And the jobs ahead like cutting back, shifting things and tucking compost into empty beds feel less like chores and more like gentle pottering. Nothing dramatic. Just good work, done in good weather, with the odd pause for tea and the satisfaction of knowing what you are doing will help shape the garden next year. The year may be turning, but it hasn’t turned yet. So, lace up the boots, man your wheelbarrows and let’s get cracking.
Hylotelephium spectabile (aka Sedum)
There are show-offs in every family. In the world of late-season perennials, sedums are unashamedly your charming, child- and responsibility-free relative who turns up fashionably late to everything and annoyingly steals the show.
Hylotelephium spectabile, or the sedum as it’s usually known, comes into its full glory in September. Its fat, fleshy leaves hold water like a camel and form the perfect stage for the star turn: flat clusters of dusky-pink flowers that hover somewhere between architectural and absurd. Butterflies love them. So do bees. And so should you. There are many varieties – ‘Autumn Joy’ being the most classic, but ‘Matrona’ is worth a punt for its bronzy stems and a certain moody sophistication.
Plant: They thrive in full sun, well-drained soil, and keep perfect company with grasses, asters, or anything that leans a little toward the wild side. Earlier this year I moved a very large, mature clump later than would be advisable with no ill effects. Who doesn’t love a plant that won’t wither at the sight of a spade?
Care: The seed heads, if left, will stand proud through winter like sculptures. Covered in frost on cold mornings, they’re unexpectedly beautiful. Don’t let their easy-going nature fool you. Sedums are workhorses and they’re precisely what a September garden needs, a little structure, a little surprise, and a splash of unapologetic colour when everything else is winding down.
Dividing Perennials
If your border looks a bit like a band that’s had one hit too many, tired, overgrown, and just slightly off-key, then now is the time to gently take it in hand. Perennials like daylilies, hostas, and geraniums benefit from being divided every few years. Don’t overthink it. Spade in, lift the clump, and tease it apart into generous chunks. Replant with a bit of peat-free compost, water them in, and walk away like a hero. They’ll thank you next year with renewed vigour and perhaps a touch less floppiness.
Keep Deadheading
There’s a temptation, in September, to start hacking back like someone possessed. Hold your horses. While it’s good to keep deadheading roses and annuals to extend their flowering, there’s no need to blitz everything. Leave some spent flowers for the birds and the bugs. Let the odd seed head stand; they might look tatty now but in the depths of winter they will look effortlessly statuesque. Gardening isn’t just about control, it’s also about knowing when to let go.
Reassess Your Borders
This is one of those gentle September tasks that is oddly satisfying. Take a notebook (yes, a notebook, ditch the phone) and walk around the garden with a critical eye. Where are the gaps? What never quite worked? Where do you need more height, more colour, more drama? You’re not planting now, you’re planning. Sketch out ideas. Take photographs. Promise yourself to move that floppy phlox in spring. This is dreaming with intent.
Lawn Care
If your lawn looks like it’s hosted a festival, don’t panic. September is an ideal time to scarify, aerate and top-dress tired turf. Rake out the thatch, spike some holes (a garden fork will do if you’re feeling retro), and sprinkle over a fine top-dressing mixed with a bit of grass seed. Water it in and let the rains do the rest. Avoid mowing too short now, let it fluff up before winter.
Clear Spent Veg
This is the month when the allotment starts to look tired. That’s fine – the party’s nearly over. But don’t just rip everything out in a fit of zeal. Clear away what’s obviously finished, mangled courgette plants, collapsed bean poles, spent salad crops, but leave what’s still giving. Chard, kale, and leeks will keep going well into the colder months. As you clear, add goodness back. Spread well-rotted compost where crops have finished, or sow green manures like phacelia or mustard to keep the soil covered and nutrient-rich. It’s like giving your beds a nice warm bath and a cosy blanket before they hibernate.
Lift Maincrop Potatoes
If you haven’t already, now’s the time to get those maincrop potatoes out of the ground before the slugs move in en masse. Choose a dry day if you can, it makes the whole process infinitely more pleasant. Let the tubers dry for a couple of hours on the soil surface before storing them somewhere cool, dark, and frost-free. Paper sacks are better than plastic… nobody likes a sweaty spud.
Think About Fruit
It’s a good time to assess how your fruit bushes have performed. Blackcurrants can be pruned after harvesting (remove about a third of the oldest wood), and any tired raspberries can be gently shown the door. If you’re thinking of planting new bushes or trees this winter, start planning now. Order bare-root plants from reputable nurseries; they’ll arrive in late autumn, ready to settle in.
Net Brassicas
If you haven’t netted your brassicas by now, you’re braver than most. Or you have made peace with the pigeons. Either way, it’s worth doing, and a simple structure of canes and fine mesh will do. The pigeons are getting hungrier by the day, and kale is their equivalent of a Michelin-starred buffet.
– Final Thoughts –
September is not the end, it’s the beginning of the garden’s quieter conversation. It’s a time to reflect, reset, and enjoy the deep, golden hues of the year as it begins its gentle descent. Walk the garden slowly. Smell the dampness in the morning. Listen to the rustle of leaves beginning to drop. Take pride in what’s grown, what’s flourished, and even what has failed, because in gardening, there’s no such thing as waste. Only compost. And if you find yourself standing next to a late-flowering dahlia with a mug of something warming, wearing your old comfy jumper and thinking about what might go where next year, well then, you’re doing it right.
