Flowering
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.
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.