The most common include Fertilizer A major component of most fertilizers is nitrogen. Nitrogen promotes leaf growth in plants. Therefore, if too much nitrogen is applied, the plant will have healthy green foliage, but little or no flowers. Age Most species of trees or shrubs have to reach a certain maturity to bloom. Patience is all that is required for the tantalizing blooms to appear.
Flower buds are less hardy than the leaf buds.
Shrubs that are insulated or protected by snow cover tend to bloom below the snow line. Selecting cultivars that have hardier flower buds can reduce or eliminate this problem. Site Selection Sunlight is a requirement for many ornamental trees or shrubs to initiate flower buds. Many shrubs like lilac require a minimum of 4-6 hours of direct sunlight daily to bloom. If that requirement is not met, the plant will not bloom.