What to do in your allotment in September

Sweetcorn (Organic) Seeds - Damaun

Written by Lee Senior

As we head into Autumn, the transformation of our allotments is incredible. There’s loads of spent plant foliage to tidy and, as the month progresses, this increases as summer-cropping vegetables come to an end. It’s a great time to start a compost bin if you don’t already have one. 

September is a month of tidying and preparing for winter. At least the weeds slow down too, so any ground work goes a long way. It’s also the last chance to plant out overwintering cabbage into their final growing positions. If you didn’t have time to start them from seeds, there’s no shame in ordering a few plants! I also try to get my garlic sets in as soon as there’s space. The longer the growing season, the better. 

I ask a lot from my plot over the course of a year so I like to sow quick maturing green manures when I can. The carpet cover stops heavy winter rain from leaching nutrients from the soil. Next spring, when I chop it up and dig it in, the soil gets a much needed nitrogen boost too. Happy growing! 

Allotment flowers in September

  • For earlier flowers next spring, sow sweet peas into modular seed trays and pop them in the cold frame to overwinter. Try ‘True Fragrance’ or ‘Sublime Scent Mix’ for extra strong scented blooms. 
  • Deadhead all of your flowering plants regularly this month to keep them blooming. Enjoy the last glorious month of sweet peas, calendula, nasturtiums and sunflowers before they’re threatened by frosts. 
  • Cut dahlia flowers just before they open and enjoy watching your vase of stunning petals unfurl.
  • Keep an eye on your sunflowers as they produce seed heads this month. Even if they’re staked, they become especially top heavy.
  • It’s time to plant your spring flowering bulbs. Tulips and daffodils brighten up the allotment and make excellent cut flowers.

Allotment vegetables in September

  • Direct sow winter lettuce seeds directly into prepared soil. ‘Winter Density’ is especially tolerant to cold.
  • Sow a crop of speedy winter leaves outdoors for fresh salad in as little as three weeks. I like leaf salad seed ‘Italian mix’ for a fun mix of basil, dandelion, cress, mustard ‘Ruby Streaks’ and wild rocket. 
  • Plant autumn onion sets outdoors to harvest next July. Choose ‘Autumn Champion’ for a reliable brown onion that stores very well. ‘Senshyu Yellow’ and red onion ‘Electric’ both have excellent cold tolerance. 
  • Plant out the last of your spring cabbage plants at the beginning of the month and protect them with netting. Cabbage white butterflies and caterpillars are still active and will strip a crop. Cover your Brussels sprouts, kale and broccoli plants too.
  • Nip out the flowering spike from any leek plants that prematurely bolt in September. Dig these leeks up and cook just like usual.
  • When your peas and beans finish, leave the roots in the ground after cutting and composting the top growth. This allows maximum nitrogen to re-enter the soil from the root nodules.
  • Check for signs of blight as you dig up your maincrop potatoes. Remember to dispose of any infected plant material away from the allotment to prevent spreading the disease. Don’t worry if your top growth is infected; the tubers below ground may be salvageable. 
  • If leaves are shading the fruit of your tomato plants remove them now to help the trusses ripen.

Allotment fruit in September

  • Pick your autumn-fruiting raspberries regularly to get them at their best.
  • There’s still time to soft prune your fruit trees and bushes if they need it. Expose fruit to aid ripening, and reduce any surplus whippy summer growth.

Crops to harvest in September

  • Maincrop potatoes. Eat any knicked or scratched potatoes first, saving the clean whole ones for storing.
  • Courgettes and runner beans should still be cropping well.
  • Start harvesting your turnips
  • Sweetcorn will be ripening this month. Have a peak at a cob to check progress before picking.
  • Pull beetroot and carrots as you need them.
  • Pick your tomatoes as they ripen.
  • Other vegetables in season include: cabbage, calabrese, cauliflower, lettuce, beans, marrow, cucumber, radish and spring onions.
  • Start to harvest apples this month. Gently twist the fruit to remove them from the tree, but if they don’t come away easily, leave them a bit longer.

General September allotment jobs

  • Apply nematodes to control slugs and snails while temperatures are still mild. Moist weather gives the best results. 
  • Sow green manure on your empty beds to keep the soil covered overwinter. Cast handfuls of the seed over a prepared bed and rake over. It adds organic matter and improves the nutrient content of your plot.
  • Build a compost bin to make your own nutrient-rich compost. September is the perfect time to compost all the rich summer growth as it starts to slow. Two bins are ideal so one is always on the go. 
  • Continue to hoe and weed your plot. 
  • Check over your stored summer onions, discarding any that show signs of softness or mould. 
  • Keep on top of watering if you have a late, dry spell.
  • Cut back the top growth of Jerusalem artichokes and harvest the knobbly roots, as needed, from the soil.
  • Audit your allotment shed. Tidy up the pots and compost sacks from the busy summer and check you have enough frost protection fleece for the coming winter.

Planning ahead

  • If your maincrop potatoes showed lots of slug damage this month, make a note to grow Potato ‘Kestrel’ next year. This variety is fairly resistant to slugs, and will give you a crop even if you live in an area that’s especially prone to them.
  • September is a great time to prepare for winter. Pile healthy green growth on the compost heap and pull out perennial weeds. 
  • Order autumn planting garlic sets for putting in the ground next month. 
  • Order shallots for October. ‘Longor’ and ‘Griselle’ are two of my favourites.
Lead image: Sweetcorn (Organic) Seeds – Damaun
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About Lee Senior
Lee Senior is an experienced horticultural writer, RHS Yorkshire in Bloom judge and horticultural consultant. He has also had an allotment for over 25 years. After initially spurning horticulture as a career option, to pursue his boyhood dream of becoming a train driver, Lee soon realised he couldn’t resist getting his hands dirty to make a living. Horticultural College training led, to getting an allotment at the tender age of 18 (in the days when you could actually get a plot quickly). My gardening hero, is Geoff Hamilton” says Lee. “It was Geoff who convinced me that you didn’t have to spray everything that moved in the garden. Watching him on Gardeners’ World in the late 1980’s and early 1990’s was a revelation. I was lucky enough to meet Geoff and I’ve also more recently had the pleasure of meeting Joe Swift. Now over two decades of practical experience has taught me to work with mother nature, not to fight against her and don’t try to tame her, as so many gardeners seem to be on a mission to do. Small-scale food growing is my passion and I can’t wait for my two daughters, one who is 8 years old and the other who is 5 to hopefully pick up the baton in the future. Nothing beats the flavour and satisfaction of growing your own food. You simply cannot buy the same quality and freshness. Everyone can have a go at growing something says Lee, no matter where they live. Lee has also written his two books; ‘Pennine Way, The Highs and Lows’ which is a humorous, personal account of walking this momentous iconic walk. His second book ‘Walking in the Aire’, features 14 short walks in Yorkshire.