The first hints of autumn start to appear at the beginning of the month, with touches of gold in the edges of the leaves and a definite sense of slowing down and packing up in the garden. Colourful crab apples are glistening, and apples and pears are ripening, but there is life in the flower garden yet too, dahlias are at their peak, joined by echinaceas, rudbeckias, Michaelmas daisies, helenium and crocosmia, all punctuated by the beautiful plumes of flowering ornamental grasses.
In the vegetable garden the autumn roots and brassicas join the end of summer produce and the Mediterranean greenhouse vegetables, and make every day in the kitchen look like a primary school harvest festival celebration.
September can often feel like summer, but as we reach the autumn equinox we cross into the darker half of the year. Days are noticeably shortening, and nights are getting colder.
Top gardening jobs for September 2023
Clear out old summer bedding plants – which are most probably looking pretty tired now anyway – and plant up your pots, windowboxes and hanging baskets with winter bedding.
You will find a great amount of choice in the garden centre: violas, pansies, cyclamen, heathers, primroses, ivies and even ornamental cabbages that turn vibrant shades of pink in colder weather. Unlike their summer equivalents, they won’t grow much in the cold, dark months to come, so you can pack them in tightly: the rule of thumb is to plant them up as full as you want them to look, rather than leaving any space for growth.
The cut flower garden
Sow hardy annuals now for cutting next summer: cornflowers, marigolds, love-in-a-mist, ammi, larkspur and scabious will all do well sown now. They will, of course, also flower from a spring sowing, but if started now they will form small plants before the weather turns cold. These will bulk up quickly come spring, and produce many more flowers than spring-sown plants, and much earlier in the year. Sow them in rows, directly where you want them to flower, and then thin them out to recommended spacing (check the seed packets) once they have germinated.
Frogs and other pond creatures will start leaving the pond this month and next, seeking out a place where they can overwinter. Frogs want a damp and sheltered spot close to the pond, so build a loose stack of logs or pile of rocks that they can crawl into. Leave plenty of mess and fallen leaves around these areas too, as everything will be made use of by creatures hunting for a cosy nook in which to see out the winter. Then just leave these areas totally undisturbed throughout winter.
Cut and cure pumpkins and winter squashes now. First frosts are likely to arrive in October, and if your squashes are still out of doors they will be turned to mush. Use any sunny spells forecast to your advantage: cut the stems a short way on either side of the stalk, to create T-shaped handles to lift the pumpkins or squashes with, and then lay them out on dry ground or on cardboard or newspaper in full sun. The skins will ‘cure’ and harden, and this will help them to store well. If there is no sign of such a dry spell you can do this in a greenhouse.
Vine weevils are dreadful pests of pots. Their grubs are first laid into the soil in autumn and then eat away at roots all winter, causing plants to suddenly collapse come spring. The biological control ‘Nemasys’ is composed of several species of nematode that prey on these grubs, and it is very effective if applied now, when the grubs are active and the soil is still warm. The nematodes are microscopic and are sold in powder form which is mixed with water and poured directly onto the compost.
This is the first of the bulb-planting months, and the most important to get in first are the daffodils (Narcissi), which need a long time in the ground in order to perform at their best. Plant them into borders and underneath trees. You could also plant some pots of miniature narcissi such as white-flowered ‘Thalia’, golden, double flowered ‘Pencrebar’ or white and gold ‘Jack Snipe’, and have them ready to place either side of a path or by a doorway next spring. Also plant (in the ground or in pots) scilla, crocus, puschkinia, chionodoxa and hyacinth. Wallflowers make good companions to spring bulbs, flowering around the same time, and they can be planted now too.
Extending the season of your flowering borders isn’t just good for the gardener, it is wonderful for bees and other pollinating insects which get a great boost of late season pollen from gardens at a time when the countryside is very lacking. It can set them up for a good winter, and at the same time give us lots of beautiful flowers. If you have gaps and a paucity of flowers this would be a good time to visit a garden centre and see what is still blooming. Seek out heleniums, sedums, rudbeckias, crocosmias, penstemons and asters, which will all brighten up the late summer garden and provide lots of pollen.
How to care for houseplants
If you moved any of your houseplants outside over the summer, this is the time to bring them in: they will not tolerate low temperatures and certainly not even a hint of a frost. They can pick up pests through the summer that would wreak havoc in the house, so check them very thoroughly before they come in. Look on the undersides of leaves for scale insects and aphids, and squash or scrape them off if you find any. Remove the top surface of the compost and replace it with fresh. And turn the pot over and check the drainage holes, particularly for any tiny young slugs. Give them a good watering, allow them to drain, and then take them indoors.
This article is kept updated with the latest information.