How to Grow And Care For Dahlias

Dahlias are half-hardy perennials, originally from Mexico, introduced into the British Isles about 1789. Very adaptable, they grow well in any type of soil. They are versatile, being used for garden decoration, cut flowers, floral art and exhibition. Few flowers can match them for their wide range of brilliant colours, their wide variety of shapes and sizes, and their long flowering period. They . Tolerate extremes of climate and, even in a poor season, some kinds will produce over one hundred flowers.

Classification

In height dahlias range from the Lilliput type, 1 ft. high, to the more normal types which can reach a height of over 5 ft., although the average is about 3.12 ft.

The sizes of the blooms vary tremendously, from about 1 in. across to over 14 in. There are ten groups as follows:

DECORATIVE Dahlias

Fully double, the petals are broad and usually flat with rounded tips.

CACTUS

Narrow petals rolled or quilled backwards half their length or more, sometimes curving inwards, sharply pointed.

SEMI-CACTUS

Halfway between the previous two, the petals broad at the base and rolled for less than half their length.

(Size: These three groups are divided into bloom sizes as follows: Giant, over 10 in., large, 8-10 in., medium, 6-8 in., small, 4-6 in. miniature, not exceeding 4 in.)

BALL AND MINIATURE BALL

These have a tight honeycomb formation with short petals rolling inwards for half their length or more and rounded at the tips. Ball dahlias range from 4-6 in., miniature ball dahlias are 4 in. or less.

POMPON

Smaller more perfect than the ball dahlias and 2 in. or less in size.

SINGLE-FLOWERED

A single row of petals surround an open centre.

ANEMONE-FLOWERED

In these the flowers have numerous tubular petals surrounded by a single row of flat petals.

COLLERETTES

These have a single inner row of small petals, usually of a different colour from the larger outer row of petals.

PAEONY-FLOWERED

These resemble the singles with an open centre but have two or more rows of petals.

MISCELLANEOUS

In this group are those bizarre dahlias which as far as shape is concerned cannot be put in any of the other groups.

DWARF BEDDING DAHLIAS

These belong to any of the ten groups but must not exceed 2 ½ in. in height.

Site

Dahlias prefer an open sunny position but will still grow well in a partially shaded spot, away from trees. They look glorious when massed in a bed or border by themselves. They also fit in well with other plants in the herbaceous border, if they are placed carefully to use their various heights and colours to best effect. The 1-ft. Tall dwarf kinds will add summer colour to the rock garden, or can be planted in a bed in a retaining wall or even in a window box. Planted in tubs or other containers, they will brighten up a patio, terrace or other paved area.

Soil Cultivation

Single digging is all that is necessary. This should be done in late autumn or early winter on heavy soil, leaving the ground rough for the snow and frost to break it down; light soils can be left until early spring. Every soil benefits from the addition of humus-forming material such as farmyard manure, peat, horse manure, leaf mould, compost, straw, hop manure, seaweed, etc., dug into the top few inches.

A month or so before planting, the soil should be broken down to a reasonable tilth and a top dressing of either bonemeal or a general fertilizer should be raked into the top couple of inches of soil.

Planting Out

Dahlias can be grown either from tubers or green plants. Tubers are the roots which have formed at the base of a plant grown the previous season. They can be planted from mid-April onwards. Space the tall types about 2 ½ ft. apart the dwarf bedding types q ft. apart, and the Lilliput types 1 ft. A stout 4 ft. stake or cane is needed for the taller types and these are put in position first. Plant the tubers 6-in, deep, just in front of the cane. On poor soil put in a couple of handfuls of a mixture of peat and a little general fertilizer, into the hole and put the tuber on this, stem upwards, and fill in the hole with fine soil. Once the shoots appear above ground they are treated exactly as green plants.

Green plants are planted as soon as all danger of frost is over. Canes are put in position first and a hole slightly larger than the plant rootball is taken out just in front of the cane. A planting mixture of peat and fertilizer will help to get the plants away to a flying start on poor soil. Place the plant in the hole and fill it in with soil. Tie the plant loosely to the cane with soft twine then water the plants in well. Place a few slug pellets round each plant.

Summer Management

For the first three or four weeks after planting, hoe the soil between the plants to keep down the weeds. When the plants have developed five or six pairs of leaves, pinch out the growing tip to promote bushy growth. As the side shoots develop after this stopping they will need to be kept tied in to the cane.

The soil around the plants should never be allowed to dry out. Dahlias benefit greatly from the application of a mulch which will lessen the need for watering. Apply this in early July to a depth of about 4 in., completely covering the soil around the plants.

Flowering

The first flowers should begin to appear about mid or late July. Better quality flowers can be obtained by disbudding, which means removing the two small side buds which appear either side of the main or terminal bud. Also remove the two side shoots which appear at the joint of the pair of leaves below the flowering bud. Left to themselves dahlias produce dozens of small poor quality flowers on short stems; a little light disbudding and de-shooting makes an amazing difference.

Faded blooms should be removed to ensure continuation of flowering. This is particularly important with the single-flowering types which form seed heads very quickly. When cutting blooms for the house use a sharp knife, make a long slanting cut and plunge the stem immediately in deep water; cut in this way, dahlias should easily last a week. Cut as many blooms as you like, as often as you like.

Give the plants an occasional foliar feed. Make sure that all the plants to be saved for next year are clearly labelled with their name (if known), or type and colour.

Lifting and Storing

Lifting dahila tubers

The tubers which have formed at the base of the plants will need to be lifted and stored for the winter. After the frost has killed the foliage cut through the main stem about 6 in. above soil level. With a fork loosen the soil round the tuber then push the fork underneath and lift the tuber.

Remove surplus soil from the roots and place them stem downwards in a greenhouse, shed, garage, or spare room for about ten days to dry. While they are drying the tubers can be prepared for storage. Trim off the thin stringy roots from the ends of the tubers and cut the stem down to about 2 in. Any damaged ends of the roots should be trimmed away and the cut surface dusted with either green sulphur or a mixture of lime and flowers of sulphur in equal parts. Tie the label securely to the stem.

Storing

If a frost-free garage, shed or spare room is available, place the tubers in shallow boxes of peat or dry soil. A cool cellar makes an ideal storage place. Where frost protection cannot be guaranteed, protect the tubers by placing them in stout wooden or cardboard boxes filled with an insulating material such as dry soil, sand, ashes, straw or sawdust.

Inspect the tubers once or twice while they are in store to make sure they are sound. Feel each tuber; if any parts are soft and brown this indicates rot which will have to be trimmed away and the cut surface dusted with sulphur/lime powder. Any tubers with a white fluffy deposit (mildew) will need to be wiped clean with a dry cloth and dusted with sulphur/lime.

Propagation

Dahlias are very easy to propagate, whether from seed, division of tubers, or by cuttings.

Sowing seed

Plants will not reproduce true to type or colour from seed, except for the single Coltness type and the semi-double dwarf bedders.

Sow the seed in March in a heated greenhouse, thinly, in pans or boxes of John Innes seed compost or one of the soilless seed composts, covering the seed with1 in. of compost. Once they germinate they should be pricked out 24 to a box. Grow the plants on coolly and in April move them to a cold frame to harden off before planting them out in late May or early June.

Dividing tubers

A dahlia tuber consists of a stem which is attached to the crown or collar where the eyes or buds are situated; swollen, potato-like tubers are attached to the crown. There are two types of tuber; the ground tuber is usually quite large and is formed at the base of a plant grown outdoors without restriction; the pot tuber is small and compact and is formed at the base of cuttings grown throughout the season in pots.

Before dividing the tuber the eyes must be visible and are coaxed into life by placing the tubers in moist peat or compost in late March or early April in shallow boxes which are placed either in a greenhouse or cold frame or on a sunny windowsill in the house. Once the eyes are visible, cut down the centre of the stem between the buds, right through the tuber. Further division may be possible, depending on the size of tuber and the position of the eyes, but each piece to be planted must contain a portion of stem attached to a piece of the crown bearing an eye, and at least one portion of swollen root or tuber. The divisions can either be planted out in mid-April or grown on in boxes in the greenhouse and planted out in late May.

Taking Cuttings

Large numbers of cuttings can be taken from dahlia tubers; they root easily in a warm greenhouse in a minimum temperature of 60 F (16°C). If any tubers show signs of rot or mildew, treat them as described earlier. The tubers are boxed up in moist peat or compost, or they can be bedded down on the open greenhouse bench, if possible, over some form of bottom heat. Keep the compost moist.

The cuttings are taken when the shoots are 3-4 in. long and are normally placed round the sides of a pot or pan or placed in a seed box in rows.

With a clean sharp knife cut through the shoot just below the lowest leaf joint. Trim off the lower leaves, dip the end of the cutting in a hormone rooting powder then place the cutting 1 in. deep in the compost. Space the cuttings so that the leaves are just clear of each other and water lightly. Place the cuttings in a propagating frame, or bed the pots in moist peat on the open bench and provide shade.

Spray the cuttings with a fungicide to prevent damping off and after a day or so allow them a free flow of air. To lessen the risk of flagging, spray the cuttings with tepid water twice daily until rooting takes place in about 14 days.

Pot the rooted cuttings singly into 3 ½-in. pots of JIP1 or a peat-based compost. Keep the plants in a shade spot in the greenhouse for a day or so before placing them on a shelf near the glass, keeping the greenhouse well ventilated. In April remove the plants to a cold frame, keep the lights closed for a couple of days then progressively allow more ventilation until, towards planting out time in late May or, in the colder areas, in early June, the lights can be left off completely. At all times protect the plants from frost.

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