Summer bulbs to lift or leave

A Gladioli flower bulb onion.  PA Photo/thinkstockphotos.
A Gladioli flower bulb onion. PA Photo/thinkstockphotos.

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.