The most banal causes are: received less food, close planting and prolonged "mestorozhdenie" bulbs.
Food
Lilies prefer to live in loose fertile soil. These plants differ endurance. They will adapt and will survive on poor soils. But for good flowering they need to feed and loosen.
Each element is important in the diet of lilies. So, if there is insufficient nitrogen in the spring, the leaves will be pale and small. A lack of phosphorus the size of the flowers, their number in the inflorescence will also be small. Upon receipt of potassium follicles will not gain weight, and they formed the whole stock of food and flower buds. And accordingly, the plants will go into hibernation weakened.
Watering plants in early summer, after flowering and in dry weather is a necessary component of success in the flowering lilies. Lily can not be watered on the leaves, watering is carried out only at the root.
Emerging capsule with seeds in inflorescences of better crop, so plants are not consumed additional power. Of course, seeds can be planted, but will grow out of them a variety of lilies. 
When the vase life of the buds for bouquets also should not be very low to expose the stem. On the stem it is necessary to leave part of the leaves that continue to nourish the bulb until late autumn. Over the summer, the bulb is growing, gaining weight and her health depends on a good wintering and flowering in the new season.
Landing
Planting dates, soil acidity may vary in different species and varieties. A single rule for all lilies is proper depth of planting and spacing plant bulbs. Everyone knows the expression that the depth of planting any bulbs is equal to three heights of such bulbs are always working. 
It is only necessary to maintain a distance between the planted in the soil with the bulbs. This nuance is often missing growers, forgetting that one of the bulbs a few years in the "nest" will be a big happy family. 
Low grade seated not less than 20 cm, the average height of a grade - not less than 30 cm tall lilies and mainly new hybrids (OA, LO, OOT, etc.) require even more area of residence and the distance between them should be between 40 cm and more.
Transplant
In the first year planting bulbs, even if they bloom, the buds are preferable to cut. Peak flowering of lilies falls on the second and third year of cultivation. 
With good care and in the fourth year the bloom will be good. But then the plant dramatically reduces its growth, the flowers become smaller. This is a signal to the florist time to do the transplant lilies to a new location, to share the "family nest".
