What to do in your garden this month

This monthly guide is geared to London gardens and their unique conditions. Compiled by the RHS Wisley Plant Centre team
Dahlia 'Gallery Rembrandt'
Continue to dead-head dahlias, like this 'Gallery Rembrandt' variety, and give a high potash liquid feed to encourage later flowers

Must do in your garden this month

* September is the time to repair your long-suffering lawn after the dry summer. Rake out any build up of “thatch” and then apply an autumn lawn food to re-establish a strong root system for the coming winter.

* It’s bulb-planting season. Narcissus and daffodil should be widely available. Perhaps this year, if you haven’t done so already, buy varieties that are early-, mid- and late-flowering and plant them together for a succession of flowers.

For expert advice on the huge array of new bulb varieties, visit homesandproperty.co.uk/outdoors.

* Continue to dead-head dahlias and give a high potash liquid feed to encourage later flowers. In protected areas you should be still getting flowers in late October.

* Late-flowering clematis varieties will also benefit now from a dusting of fish, blood and bone to build them up for next year’s flowering. Remember the feed roots are about 50–60cm away from the base of the plant, so a ring of feed hoed in around this area will give the best results.

* As vegetable crops start to go over, pull out the host plants and compost them, then prepare the ground for sowing next spring. A crop of Aquadulce broad beans can be sown now for an early crop next June.

* During the hot weather slugs and snails will have been dormant and with the lowering temperatures and increasing early dew levels vigilance is now needed in watching out for damage by these emerging pests.

* As summer tubs and baskets start to fade, turn them out and check the soil for vine weevil grubs before adding the contents to your compost heap. The best way of dealing with the grubs is to empty containers out on to an area and spread the contents for the birds to rake through. The resident robin at the RHS Wisley Garden Plant Centre waits patiently every autumn for them to empty out the display baskets!

* Be prepared for early frosts by getting some horticultural fleece material which you can use if an overnight temperature dip is forecasted. You can just drape it over vulnerable plants and so keep them flowering for longer.

* As roses start to drop their leaves, be ready to rake them up to stop any fungal spores entering the soil and laying dormant to start up again next spring. The heat from a compost heap properly maintained should kill the spores off.

* Ornamental grasses should be at their best this month so visit gardens to get inspiration and names of exceptional ones to use next year if you haven’t discovered them yet.

Planting bulbs
© John Trenholm/RHS
It's bulb-planting season, so choose your favourites, or try some new varieties

Nice to do in your garden this month

* Rooted strawberry runners should be ready to be detached from their parent plants. Put them in a sheltered position for the winter and check occasionally for pests. These are your fresh supplies for planting next spring.

* Get books out on planting combinations and use them to plant up good colour mixes of spring bulbs in conjunction with your existing herbaceous plants. A really good early spring combination is emerging mahogany-coloured Peony shoots coming up through pale-yellow dwarf narcissi.

* Iris rhizomes should be available in pre-packs in garden centres. Remember when you plant them to make sure the rhizomes sit on the soil surface so they can be baked by summer sun to encourage flowering.

* Remember to layer your compost heap with compost accelerator as you add plant material, also if you are adding lots of lawn clippings make sure you add other bulkier plant material to open up the clippings to aerate the compost.

* Your winter baskets should be planted up by now to get them rooted for the winter display. At the end of the month it’s the turn of the tubs and containers which should have more compost to insulate developing root systems. Remember to add two or three layers of bulbs to the compost as you start to plant them up so that you get a continuous display of spring flowers. Large-flowered daffodils go in the bottom of the pot; next add a layer of double early tulips; and finally add a layer of crocus near the surface of the compost.

* In your greenhouse any green tomatoes can be ripened by hanging a ripe banana among the trusses. The ethylene gas produced by the ripe banana should start the ripening process in the tomatoes.

* Plants that have been outside and are now returning to the glasshouse or the house will benefit from a spray over with a weak plant food to give the leaves a spritz before the dry air of being taken indoors. Remember humidity is a key to healthy indoor plants.

* Plant up a container for outside your back door with scented winter plants such as Sarcoccoca, Christmas box, white cheerfulness and fragrant leafed thyme.

* Finally, plant up prepared Hyacinths for Christmas displays. They should be individually potted in 9cm pots and left outside in a sheltered place until the roots are fully developed before you plant in bowls. Growth must start before the end of September to get flowers for Christmas.

All images provided courtesy of the Royal Horticultural Society. Visit the online print shop at www.rhsprints.co.uk.

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