Why do plants fail to flower?

Press, 19 September 1980, Page 6

Why do plants fail to flower?

GARDENING

M. Lusty

Disappointment’ is understandable when plants fail to flower. This naturally means that there will not be any fruit, which can be doubly upsetting,, yet the reliance on the presence of the former in order to achieve the laiter is sometimes not appreciated.

A lack of flowers can be caused by a number of factors which may be deduced and overcome in many instances. There are also far less obvious reasons and causes, which in some cases cannot be readily explained. Young plants often take a number of years to establish themselves, and during this time they may produce very.few, if any, flowers. This: may be more pronounced in some of them; for instance, magnolia campbellii may take seven .to eight years to begin to bloom. The method of propagation can greatly influence the onset of flowering. Vegetatively produced plants —those which have been grown from cuttings or by means of grafting — invariably become fieri-. ferous earlier than those raised from seed. The difs ference may sometimes be several years, for example the walnut. Excessive vegetative growth induced by too much nitrogen availability (or even an imbalance of nutrients) can inhibit

flowering. All the plant’s energies are directed towards leaf and shoot development at the expense of flower bud formation. Over-stimulus in this way is very often brought about by over-feeding, either at one time or by continuous application. Sometimes, it could even be the case that the general soil conditions are too rich for a plant which perhaps thrives in a far less fertile medium. It is also true that a lack of a nutrient or nutrients occasionally is responsible for this situation developing. A less obvious factor is the environment in which the plant, is growing. A sub-optimum condition can be caused by the amount of sunlight reaching a plant. Most plants which are grown for their flowers (and fruit) require plenty of light. This is one of the possible reasons why many indoor plants fail to produce flowers since they are kept in too dark a position, begonias providing a fairly common example.

The hours of light to which a plant is subjected

can have a direct bearing on the rapidity with which it comes into bloom and also the number of blooms produced. This is another factor utilised by propagators who are thus able to force plants to coincide with a planned flowering schedule — poinsettias and potted chrysanthemums are examples of plants which are specially forwarded for Christmas.

Many plants, especially some of the fruiting kinds require a certain number of hours of cold temperature to enhance flower bud initiation. Where com ditions are too warm there is less blossoming and consequently less fruit.

Low temperatures can also have a delaying influence on many plants, particularly where this recurs over a period of time. They may be insufficient to kill the plant but they can do enough damage to its metabolism to damage bud formation.

This effect Can reveal itself by sudden bud or flower drop or later on still in the fruit which may also drop or be very dry. Such occurrences are not unfamiliar to citrus growers. Observant growers will also have noticed that in some years forsythias fail to produce flowers on the upper regions of the branches while the lower portions appear normal. This is quite possibly the result of excessive cold. Peaches can likewise be severely limited in their flowering capacity by extreme cold and the same may be said for various others. . •.

Low summer night temperatures can often limit the cropping potential of a variety of crops particularly if there is considerable variation between that of day and night. Cucurbits, peppers and tomatoes are prime examples which fall into this category. Strong winds, especially the north-easterly, can seriously impair fruit set if not flowering with the thrashing about of exposed vegetation. Runner beans > very commonly suffer on this account. Good drainage is of considerable importance to the well-being of most plants. Very few indeed are tolerant .of waterlogged conditions for long, and initially nutrient uptake suffers which in turn affects the plant in many ways, with gradual death of the roots only the beginning of the end. Conversely, dryness presents the other extreme and some plants are particularly sensitive to a lack of moisture; again flowering suffers. It is not unknown for the cause of scarcity of bloom to be due to the over-zealous

application of pruning equipment.

It is necessary to appreciate that flowering occurs on growth of different age and whereas roses and grapes respond to heavy annual removal of shoots, flowering quinces, winter sweet and apples do not,

when taken on a year to year basis. As a golden rule always find out something about the flowering habit of any plant before cutting it back if you wish to maintain continuity of blooms. Although we are concerned mainly With failure to flower in this discourse, fruiting has been mentioned briefly throughout.

Where flowering occurs on a regular basis but no fruit eventuates then there is a possible need for cross-pollination, particularly so with hazel nuts, pears, cherries and most plums. Finally consider disease, the activities of insect pests, frost damage and in isolated cases genetical abnormality when faced with the problem of failure to flower.