What To Do In The Garden In September

Although the growing season is slowly coming to an end, David Coton can suggest quite a few jobs that need to be done over the next few weeks, helping you make the most of what's left of summer and preparing for the arrival of autumn.

Created by David Coton on Tuesday, 29th of August, 2017.
Updated on Tuesday, 27th of August, 2019.


Ensure that the garden is full of colour for another month or so by supporting the stems of late flowering perennials - asters, sedums and rudbeckia.  Fill any gaps in the border with chrysanthemums and other autumn flowering plants. Remember to continually deadhead flowers and feed baskets with high potash fertilizer.

Planning Ahead

For the best display next spring, make sure all your daffodil bulbs are planted by the end of the month, preferably in a location that catches lots of sunshine and has good drainage. Plant at least two times their depth with the point facing up, group them together one width apart, firm in and then water if the ground is dry.

Buy specially prepared Hyacynth bulbs that are designed to flower at Christmas. Plant several bulbs together in large bowl in free draining compost and cover in grit until only the tips are showing. Store in a dark cool place and water perhaps a couple of times before December. When shoots appear, bring into a bright warm place. Use a large bowl for a single amaryllis bulb and work the soil around the roots and place the bulb on top, then leave in a warm dry place.

Plant containers for autumn and winter colour replacing summer flowers that are past their best. Experiment by using a variety of colour and foliage, pansies, viola, bulbs such as grape hyacinth, small green shrubs such as euonymus, heathers, hebe and skimmia, evergreen sedges and ferns such as hart's tongue.

Plant out spring flowering Hellebores and Pulmonaria so that they establish themselves during the autumn.

Azaleas, Rhododendons and Camellias grown in containers might be too dry, water well over the next few weeks and this will avoid buds falling off in the spring.

Trim hedges now and they will not need to be cut again until the spring. Make sure that they have a chamfered top to let in maximum sunlight. Wear safety glasses, use sturdy and stable ladders, and if you are using electric cutters fit a RCD.

Herbaceous perennials can be divided to prevent clumping and to revitalise them. If shrubs have outgrown their location or need to be moved for any other reason, this is the best time of the year to re-position them. 

Harvesting and Sowing

Focus on ripening the fruit you have, dispose of small fruit that clearly won't ripen and remove leaves that are shading the fruit.

Keep picking courgettes to prevent them becoming too big and to extend their season.

Close up of sweetcornHarvest sweetcorn, check ripeness by gently opening and seeing whether the kernals are yellow and juice is milky. Eat straightaway. Don't let Runner Beans become to long and tough.

Lift and harvest maincrop potatoes and store in a dry, cool environment.

Remove old canes from summer fruiting raspberries and also weak new growth. Tie in vigorous new shoots equally spaced apart. Autumn fruiting raspberries usually need support, this will prevent them from flopping over and make picking the fruit easier.

Note how the fruit on the outside and higher up on an apple tree tends to ripen first, pick those apples that come off easily in the hand and, if you can't eat all of them, store any that aren't bruised in a cool dark place.

Once pumpkin skin is hard and the stalk woody and your squash sounds hollow, bring them into a warm room (about 20ºC) to 'cure' for a fortnight. They should then be ripe and can be stored long term at about 12ºC in the dark.

There's still time to sow fast growing crops such as rocket and also winter purslane, perpetual spinach and rocket to be picked through the winter until early next year. Thin turnips that were sown a few weeks ago.

Pinch out basil flowers as they rob the plant of energy and the leaves will become less tastier and coarser.

Sow hardy annuals such as calendula, nigella and papaver in soil that has been dug over and is weed free.

Winter broad beans such as 'Aquadulce Claudia' can be sown in fertile ground that won't get waterlogged.

Plant garlic as it needs about one month under 10 degrees to take. Select the largest cloves from a bulb and bury pointed end up in at least 1” soil and about 6” apart.

Tidying and Feeding 

The first leaves will be falling soon. These need to be collected and preferably composted into leaf mould.

Continue dead heading penstemons, osteospermums, heleniums, dahlias for a succession of new flowers until frost arrives. 

Composter in use in a gardenTie rambling roses against the tree, pergola etc or whatever they are growing over to protect them against autumn winds. Stake dahlias for the same reason.

Cut back the old flowering stems of euphorbia, wear gloves as the milky sap is an irritant. But don't be too eager to cut back perennials as they add interesting structure over winter especially after a frost.

Destroy plants such as lupins and delphiniums that has been affected by powdery mildew. Other plants such as roses can be treated with a fungicide if seriously affected. Particularly susceptible plants can be replaced.

Trim lavender, box and yew. Cut back large plants so they don't smother smaller ones and deprive them of light.

Continue to water trees that were planted in the spring. They need about 18 months of TLC. After rainfall mulch them with 10cm of organic matter to retain moisture.

Dig over vegetable patches while adding organic matter, consider growing a crop of green manure to add structure and fertility to the soil.

Keep feeding pots and containers with a liquid seaweed or similar as the compost will now have lost all its fertility and nutrition.

Improve the soil around trees, shrubs and perennials before winter arrives by lightly forking and mulching with compost. Make sure that the ground in the border doesn't become too dry, clematis, camellias and hydrangeas will benefit from the occasional soaking even if it is just washing up water.

Lawn Care

There is no better time to lay turf, repair patches or sow a new lawn. Make sure the turf is from a cultivated source or you are using the correct seed, rye grass is best for high traffic areas, a rye grass mix is a good all rounder. Dig up patches of worn grass and replace the top layer of compacted earth with a loam/compost/grit mixture to encourage root growth.

Water turf generously each day until it has taken and don't tread on it. 

Scarify the lawn to get rid of moss and dead grass, it might look scruffy but will soon recover.

Give existing lawns an autumn feed, lengthen the cut and aerate with a garden fork, repair bare patches using good quality seed.

Pond Maintenance

Although your pond might not be adjacent to hedges or under trees, falling leaves will inevitably be blown into it. So now is the time to invest in pond netting.

Leaves in a garden pondIf leaves are allowed to fall into the pond they will rot and noxious gases will be released together with nitrates that will encourage algae. Netting is therefore an essential task especially if you have a small pond, and this is also an effective method of protecting fish against predators and fitting heavy gauge netting is a good safety measure if there are children about.

The foliage from aquatic plants will also collect at the bottom of the pond and start to decompose, so cut off dead leaves and cut back and divide any pond plants which have become overgrown.

Filters and Pumps

The flow of water through pumps and filters should begin to be reduced although cleaning and annual maintenance can wait until later in the year.

Water Quality

The quality of your pond water should be regularly tested throughout the year, and September is no exception. Use a pond test kit and take any appropriate action.

If duck and blanket weed are still a apparent, remove what you can by hand and use a pond water treatment such as barley straw to further eliminate the problem.

If we are still experiencing warm weather, keep the pond topped up. If you use tap water to any great extent you may consider adding a treatment such as Blagdon Fresh Start.

Fish Food

With the diminishing appetite of your fish, start giving them a lower protein food and lessen the amount. Uneaten food will contaminate the water and will increase the risk of any disease.

And Finally

Continue to care for wildlife by leaving sticks and logs about for hibernating insects or buy frog boxes, bat boxes and hedgehog houses.

Drop into your local garden centre this week for everything you need for your autumn garden or visit the Autumn Gardening Shop on gardensite.co.uk


See our other Monthly Garden & Pond Blogs

What To Do in The Garden in January What To Do in The Garden in February What To Do in The Garden in March
What To Do in The Garden in April What To Do in The Garden in May What To Do in The Garden in June
What To Do in The Garden in July What To Do in The Garden in August What To Do in The Garden in September
What To Do in The Garden in October What To Do in The Garden in November What To Do in The Garden in December

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