Falling at the end of summer and the beginning of autumn, September can be a month of contrasts. Early September days are often warm and sunny but the end of the month can signal the start of autumnal storms. September is a time for harvesting, tidying, and preparing the garden and greenhouse for the cooler, more tumultuous months ahead.
Many summer flowering plants will have finished blooming by September, but you can still get colour from later flowering plants like anemones, echinacea and rudbeckia. In terms of harvesting the fruits and vegetables of your labour, the garden in September can be a bumper month for crops.
Keep reading to discover the jobs to do in your September garden and what flowers and vegetables you can plant now.
Gardening in September: what you should be doing in the garden now
Summer’s not quite over and early September can bring high temperatures and dry days so don’t pack the watering can away just yet! As well as harvesting crops, keeping your grass in tip-top condition and continuing with weeding, there are many other September gardening jobs to keep you busy. Here’s our list of garden tasks for September:
- The rate of grass growth is dependent on the weather and a warm September will mean you’ll still be needing to mow the grass regularly.
- Keep on top of watering your grass, especially if you’ve sown grass seed or laid new turf.
- Continue to keep weeds in check. Depending on the size of your lawn you can hand weed or use a spot weedkiller. Keeping your lawn healthy and well-watered is the best defence against weeds
- You can give any worn-out grassy areas a refresh by watering, applying an autumn lawn feed and over-seeding if necessary.
- Don’t stop watering! If rainfall is sparse, keep watering potted plants and vegetables.
- September is the time for many crops to be harvested. Onions, apples, pears, cucumbers, beans, raspberries, cherry tomatoes, courgettes and potatoes can be picked now.
- Get seed harvesting! As well as picking fruit and vegetables, you can carefully harvest seeds from your favourite flowers. Cornflowers, poppies, nasturtiums, marigolds and snapdragons are all easy plants to collect seeds from. Place the harvested seeds into an envelope and don’t forget to write what seeds are inside! Hand-collected seeds make excellent presents.
- Divide clumps of perennials that have finished flowering like bleeding hearts, lily of the valley, day lilies and peonies. You can also lift and divide large lavender plants by cutting the root ball into two.
- Add colour to borders with plants like late-flowering anemones, rudbeckia, sedum and asters.
- Plant colourful autumn containers to keep your garden looking beautiful.
- If you have a pond, September is a good time to place a net over it to catch any falling leaves.
- If you’ve brought houseplants outside to enjoy the summer sun, it’s time to bring them back indoors.
- Growing pumpkins or squash? They won’t be ready to harvest just yet, but you can help to boost their growth by removing any leaves that are shading the fruit, covering them with a thick blanket on cooler nights and fertilising the plants.
- Give the greenhouse a good clear out before winter. Make sure that it’s in good condition too and make any repairs as necessary to see it through the winter months.
- You can plant herbs to grow over autumn and winter.
- September is a good month to give the greenhouse windows a wash.
- Move any tender perennials into the greenhouse. This needs to happen when temperatures fall below 12-15ºC so, depending on where you are in the country, this may be next month.
- There are several flowers that you can grow in your greenhouse and plant directly outside this month. See the ‘Flowers to plant in September’ section below for more details.
What to plant in September
Although the temperature will start to fall in September, there are still plenty of flowers and vegetables that can be grown this month, both outside and under cover.
If you’re wondering what to sow in September, here’s our pick of the bunch to plant in your garden, greenhouse or allotment:
Vegetables to plant in September
September can be an excellent month for vegetable growing; the combination of still-warm-from-summer soil and cooler air temperatures is ideal for many vegetable crops.
Broad beans – For an early spring crop you can sow broad beans directly into the ground or start them off under cover, planting the seedlings out after 6 weeks. You’ll need to cover the plants with fleece in freezing weather.
Cabbage – Plant out cabbage seedlings that were started inside. Cabbages will grow best in firm, moist, alkaline soil and will take 4 to 6 months to mature.
Chinese broccoli – Fast growing and perfect for stir-fries, you can sow Chinese broccoli directly into the ground or in pots, keep the soil moist and it’ll be ready to harvest in 6-8 weeks.
Garlic – You can plant garlic outside in September, the plants will overwinter and put out new green shoots in spring.
Onions – Choose onion sets that are suitable for planting in autumn and plant now for an early crop.
Pak Choi – This easy-to-grow plant can be sown in large pots, raised beds or into the ground and should germinate quickly.
Radishes – Super quick and easy to grow, you can sow radishes into September. Sow seeds directly into the soil and you’ll be rewarded with juicy radishes a few weeks later.
Rocket – Plant rocket seeds into the ground or in pots, September is the last month for growing rocket outside but you can continue to grow this delicious leafy green inside during the cooler months.
Salad leaves – You can still enjoy fresh salad into autumn. Sow seeds into pots in a sheltered, sunny outdoor spot or you can grow them in the greenhouse or your kitchen.
Spinach – Spinach sown now will be ready to harvest in the spring. You can sow seeds into the soil or in pots. The plants will need to be covered from October if planted outside.
Turnips – You can sow turnip seeds directly into the soil and harvest the baby turnips in 6 weeks or so.
Flowers to plant in September
These are some of the best flower seeds to plant in September for welcome spring colour:
Calendula – Plant seeds 1cm deep outside where they are to flower for a display of sunshine in June and July.
Cornflowers – Sow seeds undercover in September for early blooms the following year.
Larkspur – You can sow larkspur seeds outside now.
Marigolds – Sow marigold seeds in shallow rows or sprinkle the seeds on top of the compost in pots outside.
Nigella – These beautiful flowers can also be sown outside in the ground or in pots for a burst of spring colour.
Poppies – Poppy seeds can be scattered outside where they are to grow.
Flowers that you can plant in your borders to plug gaps left by spent summer bloomers, brighten dull spots and fill pots include rudbeckia, pansies, heathers, helenium, sedum and chrysanthemums.
If you’re keen to start planting tulip or daffodil bulbs, it’s best to wait a little longer until October or November.
From harvesting tasty fruits and vegetables to preparing your garden for the cooler months, September is a rewarding month in the garden.
It’s a great time to get organised too, you can plant vegetables to enjoy in a few weeks’ time and get ahead in your spring garden by sowing pretty flower seeds.