Learning division

DAHLIAS arrived in Europe at the end of the 18th century, sent over to Madrid by the Spanish settlers in Mexico.

The plant is named after Andreas Dahl, who first regarded the edible tubers as vegetables. Interest switched to its flowers once the first varieties with double blooms were bred in Belgium in 1815 by M Donckelaar.

The new varieties were sent to England and within a few years most of the colours we have today had been developed.

Victorian catalogues listed hundred of varieties with Ball and Small Decorative Dahlias being the favourites at that time. With their long flowering period and large range of flower colour, size, shape and height, it isn't surprising that dahlias continue to be popular today.

Dormant dahlia tubers can be potted up this month to get them going before planting out in May or June. It is a simple job and the tubers need no special treatment apart from a frost-free windowsill, where they will start sprouting.

Choose a container large enough for the tuber to spread out easily and put crocks at the bottom topped with a few centimetres of multi-purpose compost.

Spread the tuber out gently then fill up with more of the compost, shaking and tapping the pot every now and again to make sure all the spaces are filled and there are no air pockets.

Water and label, then put on a light windowsill. The dahlia can be planted out in late May or when the danger of frost is over, by which time it should have grown into a healthy plant with several stems.

Dry dahlia tubers can be bought from most garden centres and DIY stores. They are usually displayed in polythene bags on stands with a picture of the eventual plant and cultural instructions. Look for a firm, healthy tuber with no sign of fungal rot, which can occur if the tubers weren't thoroughly dry before storing.

A tuber can provide more than one plant if several are needed for patio displays or in large borders and there are two ways of doing this. The tuber can be divided by putting it into a tray of peat in March and placing in a frost-free greenhouse or cool windowsill.

Bury the tuber so the point at which the old stem and fat part of the tuber is just exposed - this is where the new shoots will develop.

Once the shoots are about 5cm long, take the tuber out of the compost, place on a firm surface and cut through the old stem and the tuber, making sure there are one or more shoots on each side of the cut. A small saw or serrated blade such as an old bread knife can be used.

More divisions may be made so long as each has a strong growth point, part of the old tuber and some new roots. Plant the divisions into individual pots, water and grow on until planting time.

Dividing the tuber will give two or three plants; cuttings will provide even more.

Plant the tuber in a tray as described above. Once the shoots are 8-10cm long, cut them from the parent plant just above the growing point to allow more shoots to develop.

Trim the cutting just below a leaf joint and dip the end in rooting hormone powder or liquid. Put into a mixture of cutting compost and sand or vermiculite to a depth of 3cm and between 3-5cm apart.

Place in a propagator or on a windowsill. Pot into individual containers once they are big enough and grow on until they can be planted out.

Dahlias are easy plants and will grow in most well-drained soils. They dislike being planted under trees or in soil that gets waterlogged.

A few hours of direct sun each day is preferred but they will cope with partial shade. Tall varieties need staking as they will flop, but the supports can be hidden if the dahlias are grown in a border with other tall plants.

Weekend catch-up

Prune Buddleia davidii hard by taking each stem back to a bud a few centimetres above the surface of the soil. This may seem harsh but buddleias grow very quickly and if left un-pruned will grow into a dense mass of tall stems with all the flowers out of sight at the top of the plant.

Updated: 10:04 Saturday, March 20, 2004