7 September marks The United Nations’ Day for Blue Skies for Clean Air
16 September marks the UN’s Day for the Preservation of the Ozone Layer
- Clear spent plants and give a general tidying to plots to prevent pests and diseases overwintering.
- Do not compost blight-affected foliage or tubers of potatoes and tomato plants.
- Sow green manures in vegetable beds that are to be left fallow for the winter.
- Keep plants watered in dry spells to reduce stress and the risk of diseases like powdery mildew.
- If your soil is heavy, dig it over to allow time for weathering over winter to break it down and help improve soil structure. Add compost and leaf mulch.
- Allow winter squashes as long as possible to ripen on the plant but ensure they are harvested before the first frosts. While pumpkin and squash are ripening on the vine place boards or tiles below them to prevent the bases from rotting. (After harvesting let the skins harden or cure in the sun to help prolong storage hardiness.)
- Salad greens may be direct sown up to the middle of September, and several of these crops are ideal for containers, where slug control is easier and weeds are fewer. But crops are vulnerable to birds unless netted at this time of year. A top-dressing of nitrogen rich fertiliser in late winter will promote fresh leaves.
- After harvest, ensure that the canes of summer-cropping raspberries have been pruned; cut back to ground level ensuring no stubs are left. Select strong young canes that have grown this year and tie them in along wire supports.
- Tip-prune shoots on gooseberry and blackcurrants affected by gooseberry mildew, ensuring you remove and destroy all fallen leaves to help control the disease.
- Ensure carrots have insect mesh protection as carrot flies are most damaging in late summer to autumn.
- Apply grease bands to fruit trees at the end of September to deter winter moth.
- Plant out tender vegetables such as spring cabbage.
- Establish new strawberry plants while the soil is still warm.
- For cut-and-come-again leaves throughout autumn (and winter, if protected) sow corn salad and fast-growing oriental greens such as pak choi and mizuma.
- Salad leaves to sow now include coriander, parsley, spinach, dill, lettuce, endive, chicory, beetroot, chard, leaf beet, lamb’s lettuce.
- Greens to sow now: radish, turnips, mustard greens, Chinese cabbage, kales, mustard spinach.
- Plant sets of overwintering onions and shallots.
- Onions planted in September will mature next July. Plant them 1 inch deep in drills 2-4 inches apart. The RHS recommends autumn onion sets such as ‘Radar’, ‘Troy’ and ‘Swift.’ (RHS, The Garden, 2016, p.25)
- Sow hardy annuals such as calendula for late-spring flowering next year.
Sow for Early Spring Harvests
- Broad beans. Broad been can be direct-sown from mid-autumn from late September through to mid-spring in sheltered gardens. Sow beans 3 inches deep and 9 inches apart, two to a station. In colder areas broad beans can do well under cloches (dwarf selections do best with this.)
- Spinach. Succession sow every fortnight from late summer to early autumn. Sow seeds thinly 3/4 inches deep and thin to 3 inches apart and finally six inches apart as plants mature. Small plants can be treated as ‘cut-and-come-again’ crops.
- Swiss Chard
- Winter lettuce
- Put up netting to protect leafy crops from pigeon damage.
- Harvest pumpkin and winter squash before the first frosts, once their skins are evenly coloured. ‘Cure’ winter squash of all types in the sun for 7-10 days before storing.
- Harvest sweet corn – kernels contain a milky liquid when ripe.
- Continue to harvest autumn-fruiting raspberries. Fruited canes of autumn cultivars are best left unpruned until February.
- Lift and harvest maincrop potatoes. Store in a cool, dry place. Do not store any damaged tubers.
- Black scabby blotches and cracking on maturing apples and pears indicates scab disease. Affected fruit will not store well but can be eaten.
- Speed ripening of outdoor tomatoes by pulling the plants up and hanging it in a cool shed.
Flower / Ornamental Garden
- Plant spring bulbs such as hyacinth into pots for Christmas flowering indoors.
- Plant crocus, daffodil, muscari hyacinth bulbs outdoors by the end of September. Don’t plant tulip until November.
- Keep deadheading late-season bloomers such as dahlia and salvia to keep them flowering to the first frosts.
- Leave spent hydrangea flowerheads as the old blooms provide winter frost protection; deadhead and prune in early to mid-spring.
- Herbaceous summer-flowering perennials may be cut back, lifted and divided to propagate and rejuvenate them. Replant or pot-up divisions as soon as possible. Water well. If your soil is heavy or wet over winter it may be best to wait; plants can also be divided in the early spring.
- Relocate self-seeded biennials such as foxgloves if they are not growing in suitable locations.
- Plant trees and shrubs at the end of September while the soil is still warm.
- Shrubs can be lifted at the end of September and re-sited elsewhere as required.
- Stop feeding ornamental shrubs in containers so that they don’t put on new growth which will be vulnerable to frost damage.
- Keep camellias well watered to ensure good bud formation next spring.
- To control powdery mildew, remove and destroy infected leaves and also water regularly to reduce stress. The same is true of black spot on roses. Vigilance is key.
- Cuttings of tender perennials can be taken from late summer to early autumn. September is a perfect time to do this.
- Take semi-ripe cuttings of many shrubs. A large range of plants can be propagated this way, including hebes, privet, heathers and viburnums.
- Encourage insect-eating birds to visit your garden by installing a feeding station.
- Leave berries and rosehips on plants to provide wildlife food in winter.
- Late season butterflies like late-flowering plants such as ivy and Michaelmas daisies. In September you might see ‘Small Copper’ (whose caterpillar feed plant is common sorrel); ‘Peacock butterfly’ – who can be seen almost all year long, and ‘Speckled Wood Butterflies.’ which are shade-loving butterflies common to woods and garden hedges.
- If you have a wildflower meadow, now is the time to give it a final cut before winter, aiming to leave it about 3 inches high.
If your wildflower meadow has too much grass growing in it, add annual yellow rattle (Rhinanthus minor), which self-seeds and can help suppress grasses, making it a valuable meadow addition. Simply rake and scarify the soil, scatter seed, tamp down and then water.
The reason is that yellow rattle is a semi-parasite on grass, because it feeds on the chlorophyll produced by grasses, which weakens the grass plants, allowing space for the yellow rattle to shed its seed. Yellow rattle is also good if your soil is too fertile for a good meadow, as it will help keep grasses at bay, giving time for your perennial wildflowers to establish themselves. As an added bonus these plants are bee-friendly, and have yellow flowers followed by attractive papery seedheads that ‘rattle’ if shaken when dry.
- Clean birdbaths with a mild detergent to help prevent the spread of bird diseases.
- Young foxes from late litters are beginning to leave their parents.
- Bats are especially active in early autumn, laying down fat reserves for winter.
- Switch bird feed from protein rich seeds to fat balls to help birds build reserves for migration and/or winter survival.
- Lift fallen leaves from the pond to prevent deoxygenation and a build-up of silt. Leave on the side of the pond in case there are wrigglers that are able to make it back into the water.