Pollination for the Home Gardener
The home gardener faces an almost bewildering array of problems: the cost of land has reduced the amount of space available for gardening to a minimum; new varieties of plants, often hybridized for maximum production, are expensive and require a substantial amount of knowledge for successful cultivation; and the often indiscriminate use of insecticides and herbicides has curbed the population of beneficial insects, seemingly without making great headway with the horde of pests that return to haunt the gardener yearly.
Gardens still flourish in every nook and cranny of the land because of the quality and taste available in home-grown fruits and vegetables, but the economics of gardening are here to stay. It is safe to assume that for the home gardener, the labor factor is one of love, given freely in exchange for the flavor of home-grown fruits and vegetables that have no rival in any commercially-grown product. Through the use of mulches and irrigation, possible with a small plot of ground, even the weather can be controlled to an extent. Other factors of gardening can he controlled as well. The loss or non-production of one plant grown in soil of today's prices is an expense that no gardener can afford. This booklet attempts to reduce one of the risk factors of gardening, pollination, to an understandable and therefore, manageable, element of cultivation.
A flowering plant grows and if the conditions are favorable, produces a bud, which, in its turn, becomes a flower. The flower fades and fruit develops. One of Nature's most fascinating and vital cycles, fertilization resulting in reproduction, has run its course.
Successful cultivation of plants, especially those grown in a confined area such as the home orchard or garden depends upon the development of large numbers of well-shaped fruits. The development of this fruit depends upon pollination and pollination depends upon the flower.
In the plant world there are three basic types of flowers. Male flowers have only male parts and produce pollen. Female flowers have only female parts and produce fruit (See Figs. 1 and 2). Perfect or complete flowers have both male and female parts and produce both pollen and fruit. In order for the fruit to develop, the pollen produced by the male flower part must be transferred to the female flower part. This transfer is called pollination.
Figures 1 & 2
(Left) Blossoms of zucchini squash. The female blossom on the left already contains the form of the squash that will develop if properly pollinated.
(Right) The petals have been removed to show the difference in the flowers. Note the pollen-filled anther of the male blossom on the right
||Figure 3 shows a cross-section of a complete flower to illustrate this process. The sepal is one of the scales that forms the calyx, the outside covering of the bud. Inside the calyx are the petals, variously formed and colored, which have two functions - protect the inner parts of the flower from damage until pollination can take place and attract bees or other pollinating agents to the inner parts of the flower. Next come the stamens or the male parts of the flower and on top of each stamen is a sac-like anther which produces the pollen grains. When the pollen grains are mature, the anther opens and the pollen is discharged. The pollen is transferred from the anther to the stigma, the sticky end of the pistil, or innermost part of the flower.|
When a pollen grain reaches the stigma, it germinates, growing down to the ovary where it unites with an ovule which then develops into a seed. When every seed natural to the fruit is fertilized, the fruit develops perfectly. The less complete blossom fertilization, the less perfect the fruit.
Lopsided apple resulting from incomplete seed formation due to inadequate pollination
If the pollen transfers from the anther to the stigma of the same flower or to flowers of the same plant or other plants of identical genetic material, it is called self-pollination. (Editor's note: it would be more accurate here to use the term self-fertilization. The term self-pollination is oxymoronic when used with flowers that need help from a pollinator.)
The pollen of many farm crops such as grains is light and dry and is carried long distances from anther to stigma by wind-pollination. The pollen of other plants such as legumes, fruits, and many vegetables is moist and sticky and too heavy for air currents and must be transferred from anther to stigma by a bee or other pollinating agent. This process is called cross-pollination and provides a much greater genetic variety than self-pollination or the often haphazard wind-pollination.
Cross-pollination gives the plant much greater opportunity to produce mutations and adapt itself to new environments. It is because of this advantage that plants have developed flowers to attract cross-pollinating agents such as bees. Some plants have developed mechanisms to lessen or entirely prohibit self-pollination. These plants may have staminate "male" and pistillate "female" flowers on different parts of the same plant (monoecious), as in the squash or cucumber, or on separate plants (dioecious), such as persimmon, holly trees, and some nut trees. Other plants increase the chances of cross-pollination by having stamens and pistils ripen at different times; that is, the pollen of a flower may be ready but the stigma of that same flower is not ready to receive the pollen, or the reverse may be true.
BEES AS POLLINATING AGENTS
Cross-pollination is carried on mainly by insects, especially by honey bees, bumblebees, and to a very limited extent, other bee-like insects. The honey bee, of all insects, is most peculiarly adapted to the task of cross- pollination. Most insects lie dormant during the winter period and in spring come out only in small numbers, until increasing generations have reestablished the dominance of the species. The honey bee, however, lives over in large numbers among the combs of the beehive where they cluster together during cold weather, consuming the honey stored in the combs during the previous season to furnish heat and energy during the winter period. Early in the spring, the queen bee begins to lay eggs and new bees begin to grow. The urge for food has assumed sizeable proportions when fruit bloom arrives.
Bees gather nectar and pollen from flowers for food for their own use and cross-pollination is entirely incidental to this search for food. Of all the insects visiting flowers, the honey bee is the best adapted to act as a carrier of pollen. The body and legs are covered with heavy, branched hairs which catch and hold the pollen grains. The hind legs of the honey bee contain pollen baskets, somewhat concave spaces fringed with long curved hairs. The bee collects pollen, which will be a major food source for the emerging young bees in the hive, and packs it into the pollen baskets as shown in Fig. 5, Fig 6, Fig 7, and Fig 8.
Figure 5. Bee, showing pollen basket
Figure 6. The pollen grains are packed tightly with the feet.
|Figure 7. Pollen laden bees are common in the spring|
|Figure 8. You can learn to identify pollen sources|
During this process the moist and sticky pollen grains become lodged in the body hairs of the bee and may fairly cover her as she flies to another flower of the same species (See Fig. 9).
|Figure 9, The pollen lodged in the body hairs will be transferred to other flowers.|
If the bee should brush against the stigma of the next flower visited and brush off some of the pollen grains held in her body hairs, the act of cross-pollination will be completed (See Fig. 10)
|Figure 10, A honey bee seeks nectar from the
base of flowers whose ripened anthers dust the bee with pollen.
Pollen is carried among the hairs on the body of the honey bee to another flower of the same species.
Here the bee may brush against the stigma leaving some pollen, completing the act of cross-pollination.
Diagram by Charles W. Gouget
Bees also have a habit which is of utmost value from the standpoint of cross-pollination. They are flower-constant, that is, when working on blossoms for either nectar or pollen, bees seldom visit more than one kind of flower at a time. In other words, a bee that has started to gather nectar from apple blossoms will continue to gather nectar from apple blossoms until that period of foraging has ended. This constancy is of great importance as it ensures cross-pollination only within the kind of fruit being visited.
Finally, the honey bee is the only insect which can be distributed through the garden or orchard at the will of the owner. It is the only pollinating agent which is practically under his control. With proper attention to orchard and garden planting, to provide pollinating varieties discussed further on, the use of the honey bee will help ensure a satisfactory set of fruit and seed under most circumstances.
THE VALUE OF THE HONEY BEE AS A POLLINATING AGENT
Fruit and nut trees, berries and vegetables often fail to bear or produce high yields because self-sterility is very common. Self-sterile means that the plant cannot develop seed when pollinated with its own pollen. It occurs in many varieties of apples, most varieties of pears, probably in all sweet cherries, in most varieties of native and Japanese plums, and in some varieties of European and domestic plums and prunes. Even fruits which are considered to be self-fertile, that is, capable of setting seed with pollen of their own kind, will, to a high degree, set a better crop of fruit if cross-pollination occurs.
Many experiments have been conducted in attempts to set a value on the pollinating services provided by bees. Most of these experiments have produced dramatic results.
In the W. R. Roach Company orchards of Michigan, a McIntosh apple tree was screened to keep bees away from it. Throughout the rest of the orchard, bees had previously been placed in groups. The screened tree set twenty-five apples while its nearest neighbor forty feet away, where provision had been made for cross-pollination, set over 1200 apples.
In another experiment in the same orchard, one cherry tree was caged to prevent the bees from reaching it. The harvest was four pounds of cherries. Another tree the same size, exposed to bees, gave a harvest of forty-four pounds of cherries. Forty pounds of cherries is impressive evidence of the value of bees as pollinators.
While some crops are dramatically increased both in quantity and quality through the use of bees as pollinators, for other crops, bees make the difference between having a crop and no production at all! Caging experiments with cantaloupes and cucumbers have shown that bees must have access to the plants to transfer the pollen - no honey bees, no cantaloupes or cucumbers!
Figure 11 This picture tells a pollination story that every gardener should be aware of. The light-colored, undeveloped fruit at the right was a female blossom that opened when there were no male blossoms open. The blossom was not pollinated and the fruit failed to develop. The developing fruit on the left was a female blossom that opened when male blossoms were also open and there were bees to complete the cross-pollination. Result: one fine Zucchini squash in the making.
There are almost five million colonies of honey bees (Ed note: less than three million today) in the U.S. and each of these colonies may contain up to 80,000 bees, all from the same queen. These honey bees produce about 200 million pounds of honey every year but for every dollar the beekeeper realizes from his bees, the public benefits by $100 from their pollination activities. Honey and beeswax production is a small item when compared to the total value of all agriculture. But when the value of bee pollination, crops aided by bee pollination, and crops dependent upon bees for seed are all added up, the value is equal to about one-third of all the U.S. agricultural production.
Studies indicate that about 90 crops in the U.S. depend upon bees at least to some extent for pollination, and bees, overall, are credited with over one-third of the food we eat because of their pollination of farm crops. Bees also contribute to the overall environmental balance by pollinating many seeds, berries, and fruits used in food chains of wildlife.
WILD BEES AS POLLINATORS
In an earlier day there were enough wild bees to successfully pollinate field and garden crops but this is not the case today. As agriculture developed and more land came under cultivation, the nests of the wild pollinating insects were destroyed. Heavy grazing of land took a further toll, as did the elimination of rail fences and hedges. Planting of large areas to a single crop, forest and grass fires, and the automobile and paved roads added to their destruction. Housing developments and entire suburbs mushroomed out from cities and brought once natural habitats of pollinating insects under immense changes. The final step was the widespread use of insecticides, which destroyed beneficial insects as well as those which were harmful, and the use of herbicides, which not only was harmful to wild pollinating insects, but destroyed their sources of food and habitats. Practically every agricultural practice, whether in a farm field or on a city lot has contributed to the destruction of wild pollinating insects.
With the decline of the wild insects, more and more of the pollination task fell to the honey bee, the only insect which man can move from place to place and control for this purpose. Today it is estimated that more than 80 per cent of all pollination required for set of fruit and seed crops is accomplished by honey bees.
Vine crops (squash, cucumber, cantaloupes, watermelon, pumpkin) have all three flower types. Most cantaloupes and related melons produce staminate (male) flowers as well as hermaphroditic (perfect) flowers, while most cucumbers and watermelons have both staminate and pistilate flowers. They all have many seeds and each seed was formed by the union of the contents of a single pollen grain and a single ovule. Inadequate pollination will result in underdeveloped and misshapen fruits. In the case of cucumbers and other plants where the sexes are produced in separate flowers, there will be no fruit set at all unless bees are present to perform cross-pollination.
Figure 12, In this closeup of a cucumber vine in bloom, the female fruit-producing blossom is open and ripe for pollination but the surrounding male blossoms have already closed. Fruit will not develop here unless other male blossoms are open, elsewhere on the same vine or nearby on other vines and there are adequate numbers of honey bees to transfer the pollen from the male to the female blossoms.
As illustrated by the cucumber shown in Fig. 12, most of the vine crop flowers are only open for brief periods of time. Male flowers usually appear first, followed by the fruit-producing flowers. The timing of the act of pollination is crucial. Remember also, as in the case of melons, that the fruit produced nearest the crown of the plant is often sweeter, larger, and better-shaped than those produced elsewhere on the same vine. To obtain the choicest fruit, which after all is one of the goals of the home gardener, it is necessary to provide adequate numbers of honey bees to transfer the pollen as soon as the fruit-producing flowers appear.
SMALL FRUIT POLLINATION
Most of the berries such as the ones listed below depend upon bee pollinators to produce high yields and well-developed, full-fleshed berries that are the pride and joy of the home gardener:
Berry flowers have many pistils and each must receive its grain of pollen before it can contribute to the size, shape,and taste of the fruit to come. The degree of response to insect pollination differs with variety. The drawings below from the Washington State University will help illustrate this point.
Figure 13, Normal and poorly pollinated raspberry. Poorly pollinated raspberry may average 8-23 drupelets, compared to 45-90 in well-pollinated fruits. Normal and poorly pollinated blueberry cross-section. The central fleshy portion does not develop in poorly pollinated berries.
A poorly pollinated berry crop is not worth the garden space. The flavor of the home-grown berry lies in the fleshy portion between the seeds or the drupelets as in the raspberry and if it is poorly pollinated, the berry will likely be small and misshapen, especially in areas where seeds are entirely missing. Blueberry flowers must be pollinated by bees or there is no fruit at all. The central fleshy portion between the seeds in blueberries does not develop in poorly pollinated areas.
The most predominant of the home gardener's berry crop, strawberries and raspberries, will set some small and misshapen fruit in the absence of insect pollination. In some areas the native bee population will be sufficient to take care of strawberry and raspberry crops in the home garden but the gardener should watch his garden closely during the bloom period to make certain that honey bees are present (See Fig. 14 and 15, comparing poor strawberry pollination, and good pollination).Cross-pollination of berry crops are often helped with inter-plantings of two or more varieties and catalog descriptions should be carefully noted for pollination notices and requirements.
|Figure 14, The absence of cross-pollination by honey bees has taken its toll on this strawberry crop. These berries would be a diaspointment for any home gardener. (Photo, courtesy of Larry Connor, formerly Extension Entomologist, Ohio State University.)|
|Figure 15, This strawberry plant has received good pollination.The berries are nicely proportioned, and well developed, indicating that each pistilof the flower received its grain of pollen necessary to develop properly. (Photo, courtesy of Larry Connor, formerly Extension Entomologist, Ohio State University.)|
Many varieties of apples, most varieties of pears, probably all sweet cherries, most varieties of native and Japanese plums, and some varieties of European and domestic plums and prunes are self-sterile. Most of the self-sterile varieties of fruit trees will carry a pollination notice in the catalog description or the nursery salesman will point out requirements as part of his presentation. The following garden fruits and nuts are either partially or wholly dependent upon bees as pollinating agents:
The home gardener must plan very carefully before planting even the smallest orchard. If the total number of trees is limited and if two varieties of some fruits must be planted for adequate cross-pollination, careful planning is essential. In addition to knowing the pollination requirements of the intended varieties, the gardener should know something about bee behavior and the principles of pollination. Bees normally work a restricted area thoroughly rather than move great distances from tree to tree. For the gardener with a limited space this means that the trees should be clustered in one area rather than scattered over the lot. Ideally, every tree of a variety that requires cross-pollination would have a tree of the pollenizing variety next to it. With the advent of dwarf fruit trees the problem is not as severe as it once was as several dwarf trees may be grown in the space formerly required by two or three full-sized trees.
Honey bees fly freely only in warm, sunny weather. In early spring the pollination of many orchard fruits may be greatly limited by unfavorable weather. There may be only a few hours of weather suitable for insect visitations. As wild insect populations are very low at this time of year, it is wise to have an excess number of honey bees available to ensure adequate pollination.
Apple. Many varieties of apples are self-sterile and require another variety to obtain adequate pollination so two trees will have to be planned for instead of one. For the amount of space available in most home gardens, this means very careful planning. Most of the early and late blooming varieties overlap sufficiently in their bloom periods to permit satisfactory pollination of one variety by another but if choosing a variety specifically for its value as a pollinator, be sure to choose one blooming close to the principal variety. Apple blossoms produce more nectar than most fruits and are quite attractive to honey bees in or near the orchard. One colony per acre of mature orchard is considered a minimum.
Cherry. Tart cherries are self-fruitful but the presence of honey bees during bloom will greatly increase pollination and yield. Sweet cherries are self-sterile and must have interplantings of a pollenizing variety and honey bees to pollinate the blossoms. Descriptions in catalogs and nursery representatives are sources for compatible varieties.
Pear. Nearly all varieties of pears are self-sterile and mixed plantings are necessary for pollination and yield. With few exceptions, any one variety is suitable for pollenizing any other variety but a careful check of catalog descriptions for compatible varieties is always wise. Pear blossoms are not as attractive to bees as other fruit blossoms and pears will require more bees per acre to achieve the same pollination and yield as obtainable from other fruits.
Peach. Most varieties of peaches are self-fruitful although the presence of honey bees will increase the pollination and yield. Bees readily work peach blossoms and the only factor the home gardener has to watch closely is to be sure that varieties chosen are self-fruitful and if not, that compatible varieties are planted.
Plum. Most varieties of plums are self-sterile and will require a compatible companion planting. The period of bloom seems to vary widely and companion plantings must have a period of overlapping bloom to achieve pollination.
Taking the pollination requirements carefully into consideration and by choosing carefully among the many varieties offered, the home gardener might well build up a valuable home orchard. By choosing dwarf or semi-dwarf varieties, an orchard of perhaps two pear trees, one tart cherry tree, two apple trees, and two plum trees could be placed well within the confines of the average lot. By working fruit trees carefully into other plantings, the number might be increased to provide a wide variety of home-grown fruit.
One note of precaution. Do not use poisonous spray materials while the blossoms are open and bees are present. Honey bees may be protected by completely dropping poisons from any spraying schedule until after the blooming period. When pollination is in progress, spraying materially affects the germination of the pollen grains by preventing them from obtaining a satisfactory growth. This is not to say that sprays should not be used by the home gardener; rather that they should not be used during the time of active pollination by honey bees, and that they should be used carefully and only after thorough understanding of the directions for application and the effects to be expected from any particular pesticide.
OBTAINING BEES FOR POLLINATION
The commercial fruit-grower has less of a problem than does the home gardener in obtaining adequate numbers of honey bees to ensure good pollination of his fruit trees resulting in maximum yields. The commercial fruit grower contracts for pollination with a beekeeper at a set price per hive of bees and it is then up to the beekeeper to supply the colonies of bees in peak condition at precisely the right moment of bloom, set the colonies in the orchard and then remove them when the pollination service is finished. The home gardener is not likely to have such a service at his disposal and the expense involved for such a small number of trees would be prohibitive anyway.
The home gardener is then left with two choices - he can garden on the hit-or-miss basis and hope that there are enough wild bees in his area to achieve adequate pollination and enough of a yield to make his plantings worthwhile - or he can take positive steps to make his efforts pay off and that is what this booklet is all about.
Figure 16, A small colongy of honey bees has found a congeneal home on one end of a suburban garden. They provide adequate pollination for the fruit trees and garden crops and an abundant supply of fresh honey.
A small colony of honey bees can nestle very comfortably into one end of a garden setting as shown above in Figure 16. I n addition to having a dependable ready source of honey bees for pollination purposes, the gardener has the bonus of fresh honey collected from his own sources, and the fascination of a new hobby that pays for itself.
Hives like the one shown above are available in do-it-yourself hobby kits and hybrid honey bees are available in packages, grown in the South and shipped to all areas of the country to arrive in time for early fruit bloom (apricot and pear and ending with apple bloom some four to five weeks later). Usually each package contains two pounds of bees and inside the package a young queen bee is confined to a separate small queen cage suspended by a wire, and a small can of sugar syrup is included to feed the bees en route. Complete instructions for installing the hive and the bees, and handling the bees are available from the Hamilton address or any one of the branch addresses on the back cover.
In summary, bees are an essential link in one of Nature's most fascinating and vital cycles, fertilization resulting in reproduction, resulting directly or indirectly in the production of food upon which we depend for our very existence. Years of study and research have brought us to an understanding of this vital cycle and to an understanding of our dependence upon the honey bee for its pollination services. Recent years of study and research have brought us the hybrid honey bee, especially bred for gentleness and added capacities for production. We must still, however, provide the vital connection in Nature's cycle of reproduction, and that is, provide the bees in sufficient quantities in the areas in which we want them to work for us.
*Howard Veatch, Director, Dadant Publications, A Division of Dadant & Sons, Inc., Hamilton, IL 62341. Other Dadant Publications: The American Bee Journal, First Lessons in Beekeeping, American Honey Plants, and The Hive and the Honey Bee. The use of information from many sources is herewith acknowledged. Printed in the U.S.A. for Dadant & Sons, Inc., Hamilton, Illinois.
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(Beeswax candles, beekeeping supplies and equipment, beekeeping books, and The American Bee Journal are available through Dadant & Sons, Inc.)