Although the Dahlia originated in Mexico, it flourishes in all sorts of climate, but it is doubtful whether it flowers better anywhere than in our country. In all kinds of weather, it can be relied upon to produce an eye-catching feature in any garden. The dahlia is not fastidious as to the soil in which it grows, and blooms of high quality can be grown by any novice, it thrives better under some conditions than others, and it repays extra effort and attention.
Dahlias can be grown in an herbaceous border, in mixed beds, or as a dedicated dahlia display, but however they are grown they repay some thought as to planning and preparation. When grown in a permanent herbaceous border, it is important to bear in mind that some cultivars can develop into bushes three or more feet across and four to five feet high. Such cultivars must be given adequate space for proper development, and should be securely staked. Other cultivars produce more modest plants and look well as massed groups in dedicated beds.
Anyone wishing to have a most striking flower bed in front of their home can do no better than fill it with dahlias of different cultivars in harmonious colours which will flower continuously through the summer until the first frost, and will call for admiration from all passers-by.
A wide range of types of dahlia is available these days, ranging from bedding types which can be grown from seed and costing pence, from tubers in plastic bags available in stores and garden centres, to exhibition types from specialist dahlia nurseries or from dahlia societies plant sales. Members of local dahlia societies will be eager to help novice growers to choose and obtain suitable plants, and advise on how to grow them.
Preparing for planting
Although dahlias will grow well in any soil, they thrive best in rich soil with good drainage, and one way to achieve this is to raise the level of the soil by incorporating as much humus as possible. Even though dahlias benefit from copious amounts of water, they dislike standing water, and good drainage should be ensured. Dahlia roots will grow down to considerable depths in searching for water, and it is helpful if the ground is well dug and a dressing of a basal fertiliser incorporated into the soil at least two or three weeks before planting. An organic fertiliser is best such as bone meal, or fish blood and bone, at the rate of three or four ounces to the square yard (two good handfuls) is adequate.
Planting out should not be attempted until all risk of frost is over. This will be late May in the south of the country, but in the north, mid-June might be best. Plants should be well hardened off before planting, although tubers can be planted in mid-April, but precautions must be taken to protect emerging shoots from frost. by earthing up or covering with newspaper overnight. Some growers start the tubers in a greenhouse or cold frame, and when the new growth is visible, the tubers are divided into pieces, each with a growing shoot, and then planted out in late May.
It is advisable to mark out the positions for each dahlia using a cane, the spacing between plants will be determined by the types involved. Large and giant types will require three feet apart while small and miniature types will be happily accommodated two feet apart. Dwarf bedding types can be grown as close as one foot when they will require little staking.
The Planting Operation
Before planting, young plants should be watered well and then laid out alongside their appropriate canes. A hole is taken out by the cane slightly larger than the root ball and the plant set in so that when filled in, the surface of the soil will form a depression around the stem. This is to ensure that any water which is applied can soak down to the roots and not run away. The plant should be tied to its cane and labelled. If soil conditions are very dry, then some water can be given to enable the plant to become established, otherwise it is better to encourage young plants to seek out any water in the lower soil levels. The depth of planting is not critical, but some cultivars of giant and large types benefit from lower planting, in which case the lower pair of leaves is removed and the next pair of leaves is set at ground level.
Newly planted young plants are a great attraction to slugs and snails which can decimate a dahlia bed overnight. It is essential to protect against damage by using slug pellets immediately after planting. At planting time, colonies of aphids can rapidly develop on the tips of plants and it is advisable to give a precautionary spray with a systemic insecticide.
Early Season Care
Once the young plants have become established, they make rapid growth, and it is important that the new growth is securely tied. A common method of supporting rapidly growing dahlia plants is to insert two further canes at an angle to each plant and then tie twine around the three canes at intervals to form an inverted funnel which will hold the plants firmly despite the strongest winds. An alternative method is to use wire or plastic netting with a six-inch mesh tied horizontally to the canes about two feet above ground. The plants grow through the netting and are secure against the strongest winds.
It is important to keep the plants weed free, and regular hoeing also keeps the soil open. However, by the end of June, surface feeder roots develop, and then hoeing must stop. Persistent weeds will then have to be removed by hand. Further weeding can be eliminated by applying a mulch to the soil. A vast array of materials is available for mulching from straw to spent mushroom compost, even old carpet has been used successfully. Before applying the mulch, it is important that the soil is wet, and if no rain is expected, the soil should be given a good watering.
During early summer, the plants will make considerable growth and this will attract heavy infestations of aphids. A big danger is the spread of viruses brought in by aphids, and it is important to set up a regular spraying programme using a range of insecticides. Plants should be sprayed every fortnight, preferably with a different insecticide each time, to ensure that the aphids do not build up any resistance to a single insecticide. Earwigs are often a problem with dahlias as they are difficult to control with sprays. They are best dealt with by trapping using an inverted flower pot filled with straw or a matchbox taped to a cane. Paraffin put in the hollow ends of canes can also be effective against earwigs.
When July comes, most dahlias will begin to flower. At this stage, the main growing point should be pinched out in order to encourage the growth of side shoots. This means that the first flowers will be removed, so that if early flowers are needed, the growing point should be removed earlier still. ‘Stopping’ the plant can be done in mid-June if an early display is sought, but for a spread of flowering for exhibition, stopping can be spread over a matter of weeks. Most small and miniature types can be allowed to carry all the side shoots which the plant will produce, but larger cultivars will require the side shoots to be thinned out, and in the case of giants, no more than four side shoots should be kept.
No fertiliser treatment should be necessary through the flowering season. The main requirement of dahlias is an adequate water supply. During hot sunny periods, dahlias will transpire through their leaves enormous quantities of water. Unless this can be replaced rapidly from underground water, the leaves of the plant will flag and the plant wilt. Slight flagging of the leaves during the heat of the day is not serious, but once the whole plant starts to wilt, remedial measures must be taken. An overhead spray may revive flagging plants, but water is most effectively applied during the evening and night. Unless the soil holds water well, a good soaking of the plants once a week may be necessary to keep the plants growing and flowering. A good soaking of the roots is more effective than an overhead spray and small amounts of water given more often.
If a dahlia plant is left to its own devices, each flowering stem will terminate in a flowering bud, with generally two smaller buds alongside it. The two side buds, or wing buds should be pinched out as soon as practical. This will encourage the terminal bud to grow larger and develop a longer stem thus lifting the opening flower well above the foliage. The two side shoots below the terminal bud should also be removed to encourage the growth of the terminal flower and of the stem. If bigger and better blooms are required for show, then more side shoots lower down the stem can be removed. In the case of giants, all the side shoots can be removed, perhaps leaving the lowest to survive to produce a replacement flower later on in the season.
Throughout the flowering period, those flowers past their best should be removed as with most flowering plants, ‘dead heading’ encourages new flowers to develop. The succession of flowers is helped if the plants are fed with a foliar feed and given adequate watering.
Cutting blooms for the house or for show is best done either early morning or late evening. A sloping cut should be made and the blooms placed immediately in a container of cold water. A long stem should be aimed for, so that when arranging the blooms there is plenty of stem length to show the blooms to their best advantage.
Most dahlia growers love to have dahlias in the garden and perhaps to cut some blooms for the house, but few actually intend putting dahlias in a flower show. Even so, all visitors to a flower show are envious of the exhibits with which they are confronted. Many people wonder whether they could in fact match such exhibits? The truth is that with a little effort, such exhibits are possible by a novice.
The first step is to read the show schedule and decide whether the blooms available will fit the class requirements. In many small local horticultural shows, the requirements are not as stringent as in major specialist dahlia shows, and nothing will be lost in entering a few dahlias in the appropriate classes. Judges in all shows are looking for exhibits which match the requirements of the class, which are of good quality, and free from damage or blemishes. These requirements can always be met by a little care and attention. The rest comes from experience, and this will not be gained without entering and matching one’s exhibits with other competitors, so why not give it a go!
Lifting and Storing Tubers
Sooner or later each year a frost comes which blackens the dahlias, and the time has arrived when the dahlias have to be lifted, unless of course you like gambling. In recent years, many dahlias will have survived if left in the ground over winter. Their survival will be improved if covered with straw or peat, and this must be done if plants are grown in herbaceous borders. Even so, plants will develop into large clumps giving rise to a mass of new shoots in the spring, and they are best lifted and divided and replanted in the spring. The major problem is storing these tubers over winter.
In general, tubers will survive a few degrees of frost, providing they are kept dry. Cold and wet conditions are extremely hazardous for storing tubers, but on the other hand, in warm dry conditions, tubers tend to dry out and shrivel. Some happy medium must be aimed for, and in general, a cool temperature (2-3 degrees C) is ideal and a covering of dry peat or vermiculite will stop them drying out.
Once the foliage is cut back after frost, the tubers should be lifted, and the surface moisture allowed to dry out. Some growers then set the tubers up in boxes of peat in a cold greenhouse or cold frame until they start into growth in the spring. All that is needed is protection against frost, and regular inspection against rotting. In the following spring, tubers started into growth can be split into manageable pieces or cuttings taken in order to multiply selected cultivars for next season.
- Tip 1 – Do not wait until frost kills the stem before digging – dig once foliage has been killed by frost
- Tip 2 – Store tubers under greenhouse bench directly with contact with soil either encased in soil (as dug) or washed
- Tip 3 – Cover Dahlia tubers with either: fleece, old blankets or straw to stop frost
Some cultivars do not make good tubers, others make tubers that are extremely large and take too much space on the propagating bench. It is a good idea to leave one or two plants of each cultivar in their pots, and allow them to grow in the pots which are planted in the ground. The plants will develop tubers inside the pots, and because they are restricted their size is more controlled. When the frost strikes, the pots should be dug and the tops trimmed off as with the other plants. The tubers are called pot tubers, and these are the best for propagating from the following season, and are the tubers normally sent out by nurserymen.