Pollinating and Fertilising Fruit Bushes and Fruit Trees

 

In simple terms, pollination is the transference of pollen from the anthers (the male part) of a flower to the stigma (the female part) of the same or other flowers. It is a prerequisite to fertilisation.

Pollination may be carried out in a number of ways, but, with fruit crops, insect carriers are the most common and efficient. Of these, the honey-bee is by far the most important. Bees, and many other insects, spend most of their active life visiting flowers in search of nectar and, in doing so, become dusted with pollen grains from the anthers. The pollen is then transferred quite automatically to the stigma of the same flower and to that of others as the insect moves on.

Once a pollen grain has reached a receptive stigma, given the right conditions it will germinate in just the same way as a seed germinates. The ‘root’ of the pollen grain (the pollen tube) grows down through the style and, all being well, reaches and penetrates the ovary. That is the process of fertilisation.

Although the two activities are obviously and closely linked, they are quite separate and it is therefore possible for pollination to occur without fertilisation following; though, clearly, not the reverse.

pollinating fruit treesThe conditions necessary for pollination are mercifully similar to those required for fertilisation. The temperature has to be well above freezing – at least above 40°F (15°C) and the atmosphere should be moist. If it is too cold, the pollinating insects will fail to venture out. If the air is too dry, the pollen will not be released and the stigmas will be unreceptive.

As regards fertilisation; if the temperature is too low, the pollen will not germinate, nor will the pollen tube develop.

The question of temperature can be carried a stage further because the time of year when most of our fruit crops flower is also the season when night frosts often occur. These can have a devastating effect and may completely wipe out a fruit crop for that year by killing the flowers. This is why earlier-flowering fruits, like peaches, apricots and even plums, are unreliable in some parts of the UK, unless they are given protection.

Even the earlier-flowering varieties of many other fruits are susceptible to damage. Probably the only safe ones are the cane fruits (raspberries, blackberries etc.); they flower after the frosts are over.

Little can be done for large fruit trees by way of protection from frost, but small types, young trees and all soft fruits can be adequately protected from spring frosts simply by throwing some fleece or some polythene over them when a frost is likely. Even the netting used in a fruit cage will often keep in sufficient warm air to prevent the temperature dropping too low. If you are using fleece or polythene, though, be sure to take it off the following morning or you will simply prevent the pollinating insects from reaching the flowers!

The danger signs that should alert one to the likelihood of a frost are plain enough; the days are still and sunny and the nights calm and cloudless. When these conditions occur in April and May, beware.

The object of covering the trees etc. is simple; it prevents the warm air next to the ground from rising and disappearing into the wide black yonder.

The state that the underlying ground is in will also influence the degree of damage that an air frost can do. The whole object of the exercise is to help the ground release its warmth and yet to prevent that warmed air from vanishing upwards. Rough ground, therefore, will release more heat than raked ground or grass, simply because of its greater surface area.

Another aspect of pollination and fertilisation that has to be considered is the fact that all tree fruits carry heavier crops when pollinated by another variety of the same fruit. This is called cross-pollination and, in order for it to be successful, the two varieties must be physiologically compatible (most are). They must also have a good overlap of flowering periods.

Although provision for cross-pollination should, if necessary, be made when planting new trees, the lack of a suitable and nearby pollinator is also a possible reason why existing trees are not cropping as well as they should. We have touched on this before, but gardeners in towns are likely to be better off than those in the country as regards suitable cross-pollinating varieties. This is because there is a far greater chance of another tree of the same kind being in the smaller and closer-surrounding gardens and thus providing different and compatible pollen. Any suitable tree within 100 yards should be adequate.

However, important though cross-pollination is, a lack of it is seldom the sole reason for poor fruit crops; the cause is much more likely to lie elsewhere.

Low temperatures are probably the main cause and there’s very little that can be done about that; unless, of course, they are brought about by night frosts.

Cool winds may also lower the temperature sufficiently to keep most pollinating insects tucked up indoors; that is, except the extremely tough and hardworking bumble bee. Clearly, the provision of shelter from cooling winds is going to be beneficial where they exist.

The overlapping of blossom periods is also important. There’s very little point in having two varieties side by side if their blossom periods only overlap by a couple of days or so. If the weather is filthy during the overlap, very little pollination will take place.

Find out from the place where you buy the trees if your choice is good from the cross-pollination angle.

14. May 2011 by admin
Categories: Fruit Gardening, Fruit Trees | Tags: , , , | Comments Off on Pollinating and Fertilising Fruit Bushes and Fruit Trees

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