Protect your bulbs for more colour next year

DAHLIAS may still be blooming, but many other summer bulbs, including lilies and gladioli, are now past their peak. So, what can you do to give summer bulbs the best chance of returning in future years?

Some summer-flowering bulbs can be left in the ground – crocosmia corms, for instance, just keep on producing year on year and can become invasive – but many more summer bulbs can’t survive British winters.

The general rule with summer-flowering bulbs is to wait until growth has turned yellow and died down, because leaves that are green are still alive and will be providing the bulb with energy it will need for the winter and to flourish next year.

Dahlias should be left until the growth is blackened by frost in autumn, then the stems trimmed back to about 15cm (6in) before lifting the tubers.

Lift gladioli when the foliage is dying down but before the frost can kill off the corms. If you live in a mild area you can often get away with leaving them outside all year round if the ground is well drained.

Once bulbs have been lifted, you need to clean and dry them for storage. Discard damaged or diseased ones, then clean off the soil, dead foliage and any loose skin from the healthy bulbs. Place them on a wire mesh rack, not touching each other, and leave them in a cool, dry, airy place to finish drying.

Dahlias can be hung up in nets in the roof of your shed or garage, or stored in stacking trays with lots of holes in the sides for air circulation.

In mild areas with well-drained soil, you can risk leaving dahlia tubers in the ground in winter. Cut the tops down and cover the area with a 10cm (4in) layer of organic mulch, bark chippings or gravel, for extra insulation.

To prevent disease during the winter, dust lifted summer bulbs with a fungicide and pack them in clearly labelled paper bags, storing them in a cool, dry, airy spot until it’s time to plant them out again. Other bulbs that need to be lifted for over-wintering include begonia, freesia and eucomis.

Lilies in the ground shouldn’t need lifting, although if we have a particularly wet winter they may die off because they don’t like wet feet while they’re dormant. If you have clay soil or poor drainage you may be better off growing them in pots and moving them under cover.

If you are growing them in pots, once blooms have faded, cut off the flower heads, removing the developing seed capsules, but leave the stems. Water and feed regularly to build the bulbs up for next year, either using a liquid feed or a controlled-release granular fertiliser. The stems will naturally die in late summer or autumn and the bulbs can be left in the pots for three or four seasons. After this, plant the whole clump in the border.

Don’t leave them out of the soil for long as the bulbs will dry out.

Cannas add an exotic touch to the garden, their deep green waxy leaves revealing scorching red-orange and yellow flowers. They are often grown in pots and in mild areas can be left outside in a sunny, sheltered position, with the addition of a 15cm (6in) layer of mulch in winter. Be prepared, however, for losses in an extremely cold or wet winter.

In colder areas, pot-grown plants should be moved into a frost-free place, or alternatively lift the rhizomes (creeping roots) once top growth begins to droop in the autumn, cut down the foliage and stems to around 15cm (6in), remove surplus soil, dry and store in trays in multi-purpose compost in a cool, frost-free position over winter.

BEST OF THE BUNCH: RUDBECKIA

THESE bright and cheery yellow daisy-flowered showstoppers with chocolate centres come into their own in late summer through to October, complementing fiery displays matched by red hot pokers or crocosmias, or in containers with purple cordyline.

Many grow to around 60cm (2ft) but there are taller varieties such as R. ‘Herbstsonne’ (‘Autumn Sun’), growing to 180cm (72in) which looks great at the back of a border in front of late-flowering clematis.

They will grow almost anywhere in full sun and reasonably fertile, moist soil. Good varieties include R. fulgida sullivanti ‘Goldsturm’, which produces a profusion of flowers, and the double-flowered ‘Goldquelle’, which grows to around 70cm and looks a bit like a zinnia.

GOOD ENOUGH TO EAT: HARVESTING ONIONS

YOU should be harvesting your onions now, but you’ll know they’re ready when the foliage collapses. Many gardeners recommend that you bend over the tops of onions to ripen them, but this usually happens naturally so you shouldn’t need to intervene. Pick a dry day to dig them up, gently easing the onions out of the ground with a fork, to break the roots’ hold on the soil. Onions need to be dry when stored so if it’s fine, leave the bulbs on the soil to dry off for about a week. If not, cover them with cloches or a sheet of polythene, or lay them out in a cool, airy shed. Once they are dry, bundle them into nets to hang up in the shed, where they will keep best in the light.

WHAT TO DO THIS WEEK

• Clip lavender to clear the dead flowerheads and reshape the plants, ensuring you don’t cut into old wood
• If you’ve been away and your containers haven’t been watered and look like they’ve had it, tip them out and start again, focusing on autumn planting schemes
• Check plants such as roses and honeysuckles for powdery mildew and try to improve the growing conditions by soaking the ground with water and giving them a high potash feed
• As rows in the veg plot become vacant, refill them with sowings of fast-growing varieties of carrots, peas and turnips, as well as lettuce and baby spinach leaves for salads
• Take softwood cuttings from tender perennials including pelargoniums, verbena, penstemons and shrubby salvias and lave them in small pots or trays in the greenhouse
• Harvest greenhouse tomatoes, peppers, aubergines and cucumbers
• Support tall-growing clumps of perennial asters including Michaelmas daisies, which are starting to flop now the flowers are out
• Clip hornbeam, beech, Leyland cypress and thuja hedges before mid-September
• Get your compost heap in order as autumn clearing generates a lot of waste