How To Successfully Grow Dahlias

Certainly dahlias are worth a section on their own. These tuberous rooted, half-hardy perennials gladden the heart of thousands of gardeners with their variety of shapes, sizes and colours. The reason, maybe, is that they’re quite easy to grow, being happy in most soils and requiring the minimum of attention. Not only that, they will flower continuously right through from July until the first frosts of autumn, providing a positive riot of colour the while!

Soil preparation is necessary. Dig over the site in winter or early spring, mixing in peat, leaf mould, manure or compost. Go easy, though, on poultry manure because this tends to boost plants into too much growth at the expense of the flowers. Additives should be mixed in just under the surface of the soil because dahlias make their roots in that area.

There are precise groups of dahlias, some of these sub-divided into types which include single, anemone, and paeony flowered. The most popular types, however, are those with flat, wide petals; those known as cactus, with petals which roll backwards in a quill; small two-inch wide pom-poms shaped like drumsticks; and the ball-shaped varieties which have a big range of size and colour.

Then there are the decorative types which fall into ‘Giant’, ‘Large’, ‘Small’ and ‘Miniature’ categories. The cactus varieties, too, are sub-divided into ‘Giant’, ‘Large’, ‘Medium’ or ‘Semi-cactus’. All this is somewhat bewildering, so much so that a National Dahlia Society has been formed as an acknowledged authority on classification of all the types. But names and categories aside, with dahlias it’s very much a case of paying your money and taking your choice.

Dormant tubers are the answer for a normal garden display. They bloom early and produce a maximum of flowers. You can start tubers in pots for flowers in May, or, planted under cloches, removing these at the end of June, you’ll have a good showing in July. But for best results plant the dormant tubers outdoors in May, after danger of frost has passed. You’ll get a good showing from July onwards.

Tubers come in two types – the ground root and the pot-grown tuber. The ground root results from years of growing outdoors without restriction. These will increase to excess and poor flowers will result. So it’s better to divide them up every second year, making sure each portion has growth buds present. Incidentally, dahlia buds aren’t found on each separate tuber, but at the base of the stems. If in doubt about division put the roots in a greenhouse and let the shoots develop; this will show the best way of dividing the tubers.

The pot-grown tuber, produced from cuttings and grown in pots during the summer, is the type offered by most garden shops.

The dahlia plant is formed by rooting dahlia cuttings and these flower later than plants grown from tubers.

It’s quite easy to keep dahlia tubers to plant out year by year. When the first frosts of winter blacken the leaves of the plant the foliage should be cut to about nine inches above ground level. Then, with a garden fork, lift the tubers out of the ground, taking care not to spike and damage them during the process. Shake off the soil and stand the tubers upside down somewhere dry and well ventilated and frost-free. They must be thoroughly dried out and the stems retrimmed to just above one tuber before they are stored – for example, packed in dry peat, in boxes. The peat will act as a protection against frost and it will also absorb any excess moisture. It makes sense, too, to store them in a deep frame, packed with leaves as a precaution against frost, and sited against a south wall. The frames should be weighted down with mats or something similar so that they’ll stay in place when the wind blows hard.

Stored tubers ought to be inspected every month. Any parts which look as though they’re rotting must be cut away. You can buy preparations in powder form which will seal the wound. If you keep your tubers covered, and this isn’t strictiy necessary provided they’re placed in well-ventilated, frost-free conditions, for goodness’ sake don’t fall for the ‘out of sight out of mind’ formula and forget about them! They’ll need a monthly inspection just the same. A temperature of between 40° and 50°F is ideal for storage conditions, by the way.

One more point. Always label tubers before you put them to bed for the winter, otherwise you may forget which are giants, which are pom-poms and so forth.

You can, if you like, take a chance and leave the tubers in the ground all winter, if this promises to be mild or if you live in a very sheltered part of the country.

After storing, plant the tubers out at the end of May, by which time all danger of frost should be passed. Put in stakes to support the plants beforehand, not afterwards or you may damage the tubers. The top of the tuber should be about two inches below ground, and two feet apart for pom-poms, a little bit more for ball dahlias, and at least three feet for the giant types.

The usual way of propagating dahlias is to take cuttings. Take these from shoots which grow from the base of the stems which are attached to the tuber. Take the cuttings when they’re three inches long, removing the lower leaves and trimming them cleanly just below a joint. Dip the cuttings in a rooting compost and pot them in sandy compost. When plants are established, pot on to five-inch pots. Incidentally, don’t forget to leave enough space at the top of the pots so that you can water properly, and do plant firmly. And when your plants are really in action, when buds are pea-sized, remove them, allowing the centrally placed bud to remain. If left they’ll run amok and poor quality blooms will result… and then what will the neighbours say?

Dahlias come in a big range of colours, sizes and shapes. Their height varies from three to four feet down to those which grow to about eighteen inches (I.e. the Border variety, bottom right). Treat them right and they’ll flower through from August until the first frosts of winter. The basic types are illustrated below, but there are several variations of each.

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