September in Your Garden
The chill is in the air this month and the smell of autumn bonfires carries on the breeze but there is still plenty to enjoy outdoors
• Divide early flowering herbaceous perennials such as Astrantia, Hosta and Geranium
• Continue picking autumn raspberries
• Collect and sow seed from perennials and hardy annuals
• Dig up remaining potatoes before slug damage spoils them
• Net ponds before leaf fall gets underway
• Keep up with watering of new plants, using rain or grey water if possible
• Start to reduce the frequency of houseplant watering
• Clean out cold frames and greenhouses so that they are ready for use in the autumn
• Cover leafy vegetable crops with bird-proof netting
• Plant spring flowering bulbs ordered early in the year.
Herbaceous and Annuals
Sowing and planting
Sow sweet peas in a cold frame or the greenhouse for early summer blooms next year.
Sow other hardy annuals (e.g. Consolida, Calendula, Centaurea, Limnanthes and poppies) in situ.
If you sowed any spring-flowering biennials such as Viola, Digitalis (foxglove) or Erysimum (wallflowers), earlier in the summer, they will now need planting out.
This is a good time of year to plant new perennials, especially towards the end of September, as the soil is still warm, but moisture levels are increasing.
Cutting back, pruning and dividing
Don't neglect hanging basket maintenance - a little deadheading, watering and feeding can keep them going until mid-autumn. Once they are past their best, re-plant as winter/spring hanging baskets with spring-flowering bulbs, winter heathers, trailing ivies and spring-flowering plants as above.
Continue to deadhead plants such as dahlias, delphiniums, roses and penstemons to prolong the display and give colour well into the month.
Continue cutting back perennials that are fading and dying down.
Now is a good time to divide any overgrown or tired looking clumps of alpines and herbaceous perennials such as crocosmias. This will invigorate them, and improve flowering and overall shape, for next year.
Take cuttings of tender perennials, such as Pelargonium and Osteospermum. These plants often do better grown from new cuttings each year. If you do not have a greenhouse, then use a light windowsill to grow them on.
Continue collecting and storing seed from perennials still forming seed heads.
Shrubs and Trees
Planting and moving
If the weather is already autumnal, you can now plant and move shrubs and trees without having to worry excessively about their survival and establishment. Shrubs planted now will get off to a flying start next spring, as they will have had all winter to settle in.
Pruning and training
Give evergreen hedges a final trim to make sure they are in shape for winter. This is particularly useful for fast-growing hedges such as leylandii (x Cuprocyparis leylandii). Remember to cut hedges slightly narrower at the top than the bottom – this makes them less liable to snow damage in winter and stops the hedge from shading itself out at the base, which can lead to dead patches.
Take semi-ripe cuttings of evergreen shrubs such as Cistus, Ceanothus and Viburnum.
Thoroughly soak drought-stressed plants and shrubs, especially newly planted ones. As the weather becomes cooler and damper, the soil will better absorb and hold any extra water you give it.
Clear dead leaves promptly once they start to fall, as rotting leaves can be a source of disease in the garden. They are, however, useful on the compost heap and can be shredded first with a shredder or mulching mower, to help them break down quicker.
Collect tree and shrub seeds for sowing next spring, such as Colutea (bladder senna), Laburnum, Morus (mulberry) and Sorbus (rowan).
Order mature or large plants now for planting in October or once the rains have moistened the soil.
Pest and disease watch
Good garden hygiene helps to prevent disease, so it is vital to throw out or destroy diseased leaves. Do not compost them or leave them lying, as this could spread the disease.
Saprophytic fungi (i.e. living entirely on dead matter) pose no threat to living garden plants. Honey fungus may be more common in areas of woody planting, whereas harmless fungi often pop up in areas of damp lawn or on mulch.
Honey fungus fruiting bodies will begin to appear in late September and early October, indicating possible areas of infection. However, there are many harmless fungi that appear at this time, so don't be overly alarmed.
Powdery mildew can still be troublesome in warm, dry, Indian summer weather. Unless it is severe, it will probably clear up once the rains arrive.
Mow less frequently during autumn, and raise the height of cut as the growth rate of the grass slows down. This will help the lawn to withstand the last of the warm, dry weather, and also keep it resistant to treading as the wet weather arrives.
You can harden your lawn up for winter by applying an autumn lawn feed, which is high in potassium. Do this after scarifying and aerating but before applying a top dressing. Do not give summer feeds that are high in nitrogen as this will only result in weak, soft growth, which will be prone to disease in the autumn weather.
Loam and sand top dressings are usually applied at a rate of 2kg per sq m (4.5lb per sq yd), working them into the lawn with a stiff brush or the back of a garden rake. If the proprietary product you use has specific application instructions, then do follow these closely.