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Why Plants Don't Bloom

J. Robert Nuss, Ornamental Horticulture

Under the correct set of conditions, all plants will flower at some point in their life cycle. The form and characteristics of the particular flower will depend upon the genus of plant.  A flower can range from the extreme beauty of an orchid to the near insignificance of a holly blossom.  However, all flowers have their own degree of beauty if size is not considered.

It might be well to first consider some of the factors necessary for flowering in an effort to better understand why flowering may not occur. First of all, what is flowering?  It is a series of biochemical changes which alter the pattern of cell differentiation from leaf, bud, and stem tissue to pistil, stamens, and accessory parts Q petals and sepals.

The plant's environment plays an important role in flower development.  Definite factors are nutrition, light, and temperature.  It has been known for many years that the application of nitrogen will reduce flower production.  The present knowledge of growth regulators indicates that anything reducing the growth of a plant will also tend to increase flower initiation.  The length of day under which a given plant grows will influence the flowering response.  Some plants flower when the day is short, others when it is long; and a third group are not effected by day length.  Finally, a certain amount of chilling or cold is needed on some plants before the flower buds will open.  Examples would be such plants as azaleas and crocus.

If all the environmental conditions are correct there is no reason why a plant will not go ahead and produce viable flower buds.  However, even though there are flower buds present, there is no guarantee that flowering will occur.  There are several events which might interrupt flowering.  Cold injury is rather common.  This can be an early freeze in the fall or a late freeze in the spring.  In both cases the plant is too tender.  Another type of cold injury results after a warm period in midwinter.  Growth can be started, only to be killed by subsequent cold.

Other events to consider would be drought injury.  The buds or plant can be dried out to a point where they are killed either in the fall or during a hard winter.  Mechanical damage is often overlooked.  Ice or wind can knock some of the larger buds from a stem. Another problem can be animals, particularly when there is snow cover on natural foods.  Finally, we may inadvertently prune off the flower buds at the wrong season.

On the other hand, there are several factors which might prevent the flower buds from forming.  Heavy pruning might encourage vigorous growth, which tends to discourage flowering. Also, heavy fertilization will often reduce the number of flowers if carried out while buds are being formed.  The same holds true for excess moisture during this bud development period. It might be that a particular plant is too young to flower or that the wood has matured past the flowering stage. When old wood is the problem, maintenance practices can generally help.

One final point we should keep in mind is that the flowers may come at an unusual time.  The native Witch Hazel blooms in January or February.  Also on some plants the flowers are very small and almost insignificant. The greenish flowers of the Japanese Holly are a good example.  Therefore if we are able to supply the proper environment for a plant and know what to look for, most of our wood plants can be a valuable addition to the landscape.

Where trade names are used, no discrimination is intended and no endorsement by Cooperative Extension is implied.

J. R. Nuss, Prof. of Ornamental Hort
Department of Horticulture
Penn State College of Agricultural Sciences
103 Tyson Bldg., University Park, PA 16802
(814) 865-2571