This Month in the Garden - September

Make the most of the late summer in September ...

This Month...

Continue with dead heading and weeding to extend the flowering season and keep soil nutrients and moisture for your plants and not the weeds.

Sowing and Planting:

Bulbs make a fine display planted in containers or borders, especially daffodils, snowdrops and tulips in springtime. They are one of the easiest and most rewarding garden plants to grow. Most spring-flowering bulbs should be planted by the end of September with the exception of tulips which should be left until November. Look out for new varieties as well as much loved old favourites. When planting daffodils in containers its worth planting two layers of bulbs, slightly staggered one above the other. This will ensure a spectacular display. Plant the bulbs deeply enough to allow you to plant winter and spring bedding, such as winter pansies, primroses, violas and wallflowers on top. 

Sweet pea lovers may find that sowing seed in autumn produces stronger plants. Do not soak the seeds as they are liable to rot. Use Seed and Potting Compost and sow the seeds in root trainers, sweet peas tubes, pots or trays. Cover the containers with glass or put them in a propagator and keep at around 15 C (59 F). When the seedlings appear transfer them to a cold frame. Pinch out the growing tips when the plants are about 10 cm (4 inches) high.

Once summer bedding has gone over, plant up containers/baskets/fill gaps with autumn and winter bedding such as winter pansies, Violas, Cyclamen, Wallflowers and Sweet Williams.

This is also 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.


Now’s the time to go around your garden collecting seeds from perennials and annuals. Collect seed heads in paper bags and leave them in a warm place to dry for a few days, before cleaning and storing in small envelopes. 

Shrub roses and ramblers can easily be propagated from stem cuttings at this time of year. Take a length of stem about 30cm (12 inches) long and trim it off just below the bottom leaf. Remove the soft tip. Take off all but the top two or three leaves and push the cuttings into a well dug trench in the garden to about half their length. They should be left for twelve months to root and develop.

Continue to take cuttings of tender perennials.

Click here to visit our seed & propagation website page.


In the south of England you can still sow quick maturing salad crops such as summer lettuce, radish, rocket, sorrel, chicory and fennel. If you’re sowing out of doors this month you can speed up germination by putting a cloche over the seeds.

Continue to sow spring cabbage, turnips, Oriental vegetables and overwintering onions.

Sow green manures such as crimson clover and Italian ryegrass to act as a soil improver and to cover bare areas. When dug in, they conserve nutrients and improve soil texture.

Pick autumn raspberries.

Dig up remaining potatoes before slug damage spoils them.

Ensure all vegetables are watered well during dry spells. A consistent supply of water will aid healthy development, and help to avoid diseases, disorders and bolting.

Prune soft and bush fruit such as plums, gages and damsons immediately after harvest.

Cover autumn-fruiting blackberries and raspberries with netting to keep off the birds, but check daily to ensure no animals or birds get trapped.

Lawn Care:

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.

Aerate and apply an autumn lawn fertilizer to nourish your lawn through the winter months. Autumn lawn fertiliser is high in potash and phosphates which will better protect the grass from frost and icy conditions. High nitrogen spring/summer feeds will encourage top growth which is soft and easily damaged by frosts which is not ideal for autumn lawn feeding.

You can continue to re-seed bare patches on your lawn. It’s also a good time of year to prepare the ground for sowing a new lawn, while the earth is still warm.

In the Greenhouse:

Damping down usually becomes unnecessary as the month progresses. It is best to do any watering or damping down earlier in the day so that the greenhouse is dry by evening. Dampness during the cool nights could be a recipe for a fluffy grey mould (Botryis) and damping off seedlings. (Damping off is a disease of seedlings caused by several different fungi and fungus-like organisms. This disease causes emerging seedlings to collapse, often submerged in a mass of white fungal growth. It is particularly a problem when sowing seed indoors or under glass.)


Continue deadheading, watering and feeding hanging baskets and planted containers to keep them going. Divide herbaceous perennials. Keep up with watering of new plants using rain or grey water if possible. 

Prune late summer flowering shrubs such as Philadelphus (Mock Orange) and give evergreen hedges a final trim to make sure they are in shape for winter. Prune climbing roses once they have finished flowering; sideshoots from the main branches can be cut back to a couple of buds. Any dead, diseased or spindly growth should be cut out and new young shoots tied in to the supports, from the base. If there is an old, thick and woody, unproductive stem, it can be removed from the base to stimulate more vigorous growth.

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.

September is an ideal time of the year to apply biological controls for use on vine weevil. Grubs will be starting to hatch, and soil and compost temperatures are now suitable for the nematodes to be effective. Target vulnerable plants, such as fuchsias, succulents and containerised plants.

Click here to visit our Pest, Weed & Fungal Control page for information.