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What to plant in September (and other garden tasks for the month)
The colours are starting to change in the borders. As plants go to seed, the intense green of spring and early summer starts to fade, replaced by shades of gold and burnished bronze. At this time of year, I start collecting seed from some of the annuals and perennials that I want to keep spreading round the garden. The best plants to choose are the species, as you know that the seed will come true; for hybrids and named forms, the resulting plants may well be different from the parent plants.
In my garden, I harvest seed from plants such as Digitalis grandiflora, Dianthus carthusianorum, Cenolophium denudatum and Ammi majus, as well as poppies, honesty and marigolds. The poppies are pot luck, as they may have crossed with other poppies. If you are particularly fond of a named seed strain, such as ‘Amazing Grey’, you will probably have to buy new seed each year in order to keep the flowers true. ‘Amazing Grey’ is a field poppy, so if there are common red field poppies nearby, the chances are that you will end up with something not quite as amazingly grey as the year before.
I harvest the seeds one species at a time, snipping the seed heads off and putting them in trays, which I shall then leave in the greenhouse to dry for a few weeks. Once that is done, I’ll sort through every-thing. It is a job that I love. There is something very therapeutic about shaking poppy capsules or ammi seed heads into an envelope or paper bag and seeing the prodigious amounts of seed you can harvest from just a few plants. If you have too many, you can make your own seed packets and give them away.
Clare's top jobs for September
- Start dividing herbaceous perennials.
- Harvest seed from early summer-flowering perennials and annuals.
- Dig up and store any remaining potatoes.
- Sow hardy annuals such as ammi, cornflowers, cerinthe and scabious for next year.
- Take softwood cuttings from pelargoniums, salvias and fuchsias.
- Sow winter salad leaves, such as mizuna and mustard greens.
- Keep harvesting vegetables, and pick apples and pear.
What to plant for September
Ornamental grasses come into their own at this time of year, many holding their shape well into winter. Woven in with late-summer-flowering herbaceous plants, they bring a mellow glow to the border, as well as movement and structure.
Japanese blood grass has ribbon-like leaves that are bright green at the base, turning crimson at the tips, and looks most striking in late summer. Liking dry, sunny conditions, it reaches 40cm and looks effective planted in drifts towards the front of a border, with heleniums, rock roses or another grass such as Stipa tenuissima. It will also do well in a gravel garden, trough or container.
This mid-height grass is a delight, with its rounded mass of feathery flower spikes that last through the summer until the end of September. However, it is not very robust and can succumb to a really cold winter, so if you live in the north of the UK it may be better to grow it in a pot, which can then be brought inside over winter. It prefers full sun and a soil that does not get too wet.
Also known as pheasant’s tail grass, this is an extremely useful grass for year-round interest, as it thrives in dry conditions, in shade as well as sun. With a height and spread of 1 metre, it has slender fronds that emerge green in spring, turning shades of golden yellow, buff brown and crimson in autumn. If grown in sun, it will produce sprays of airy pinkish flower heads in late summer; in shade, these do not usually appear, but the foliage makes up for it.
Commonly known as Japanese forest grass, this is a tough, versatile plant that forms excellent ground cover when grown in drifts. It prefers dry conditions and well-drained soil in sun or light shade, producing distinc- tive mounds of grassy foliage that emerge a fresh lime green in spring, often turning vivid shades of orange in autumn. It is much favoured by contemporary garden designers, who like to employ it to create an eye-catching contrast to unclipped evergreens or multi-stemmed shrubs.
Panicums are useful mid-sized ornamental grasses, typically reaching 75cm-1.2 metres tall when grown in full sun and well-drained conditions. Handsome cultivar ‘Rehbraun’ forms generous mounds of upright green foliage, which takes on shades of crimson in autumn, topped by clouds of soft reddish- purple flowers from late summer onwards.
This low-growing grass has striking needle- like leaves that turn an intense silvery blue if grown in full sun. Forming hummocks of foliage about 30cm tall, it produces blueish flowers in summer, which fade to gold in late summer and autumn. It is great in a gravel garden or a container with Mediterranean- style plants such as santolina and lavender.
Ten more things to do
- Pick the seedpods and heads of any open-pollinated flowers you want to grow again next year; store the seeds in a cool, dry spot in brown paper bags for sowing next spring.
- Buy spring-flowering bulbs. Choose firm, plump bulbs and avoid any with signs of mould. Plant them as soon as possible so they can start putting down roots. The cool, moist conditions of late autumn suit tulips best so wait until November before planting them.
- Early autumn is the ideal time to plant evergreen trees and shrubs so they get established while the soil is still warm. Water well after planting and should the weather remain dry, water once a week.
- Hardy annuals such as Calendula, Ammi majus, Larkspur, Nigella and Honesty can now be sown directly into the garden soil - this gives your cutting border a head start in Spring. Ensure that the earth is weed free before sowing and raked to a fine tilth. Sow the seeds and then gently rake them into the soil, before watering well. You will be rewarded with an early show of flowers next Spring.
- There are quite a few varieties of autumn and winter vegetables you can plant now for produce during the colder months - winter and spring cabbage, purple sprouting broccoli, little gem lettuce, chicory and Chinese cabbage are a few options.
- Now is an ideal time to start a compost heap in your garden - autumn's fallen leaves, your grass clippings, any teabags, eggs shells or coffee grinds will all ensure you have a wonderful organic rich compost for next spring's planting. Ensure that any good compost that remains in compost bins are used up on the garden during autumn.
- Congested clumps of perennials such as Agapanthus, Euphorbias and Geums can be safely divided in autumn. This will help encourage flowering next year and stop them from taking over your borders.
- Pests and diseases will still be present in the greenhouse - vigilance is still required, treat any you find immediately. Remove and burn any tomato plants that have become susceptible to blight. Take down greenhouse shade netting or scrub off shading paint by the end of the month as light levels start to fall.
- Net ponds and water features before the leaves start to fall, this will prevent debris from rotting in the water and blockages forming on the pumps of water features. Remove any rotting aquatic plant debris to keep the water clean of pond life during the winter months.
- The cut flower garden is still going strong - Dahlias at their peak, grasses will be looking resplendent in the autumn sun and branches will be laden with crab apples. Continue to pick Dahlias, Zinnias and Chrysanthemums regularly. Perennials such as Asters, Japanese Anemones make welcome additions to vases. Try making an autumnal door wreath from berries and seed heads and old man's beard (Clematis vitalba) - a fun project for a warm autumnal afternoon.
1/6Clare sorting through seeds in her greenhouse.
2/6The silvery seed pods of Lunaria ‘Corfu Blue’.
3/6Pink Hylotelephium ‘Herbstfreude’.
4/6Clare’s front garden at this time of year.
5/6Poppy seed heads.
6/6Seed heads of Dianthus carthusianorum.
