Do not fertilize dahlias after mid-August. When the plants reach a height of three to four inches, pinch the terminal bud just above the second pair of leaves. This will produce two main stems. When flower buds are visible, begin disbudding. This will increase the bloom size of the leader bud and improve the flower stem formation.
Flower buds come in three's.
The central leader bud will produce the largest bloom. There will be a smaller flower bud on each side of the leader bud. Remove these side buds by pinching or cutting to the base of the leaf axil. Further down the same stem, two more buds will be found in the leaf axils and these, too, should be removed. Flowers should be cut when fully opened.