Get It Growing News For 11/21/2003
By Dan Gill
LSU AgCenter Horticulturist
Botany lessons often help gardeners understand some of the underlying reasons why plants behave the way they do.
When growing a plant that is expected to produce fruit, knowing something about the reproductive workings of the plant is in the gardener’s best interest. Otherwise, you could be in for disappointment.
Plants that are grown for their attractive flowers need only to bloom well to make us happy. We even deadhead blooming plants by removing faded flowers to prevent seed formation and encourage more flowers.
Flowers contain the sexual organs of plants and are produced by plants in an effort to reproduce themselves. When fruit or seed production is the goal, the sexual nature of flowers and their function become very important to the gardener.
The strategies plants have evolved for blooming and pollination are incredibly varied, and gardeners need to be familiar with any quirks associated with the plants they are trying to grow. For those plants that we grow for their attractive or edible fruit or seeds, how successfully the plant carries out its reproductive efforts has a direct effect on obtaining the desired fruit or seeds.
Note that in botany and horticulture, the term fruit basically indicates the structure a plant produces that encloses the seeds. For example, peppers, green beans, tomatoes, squash, peaches, holly berries, okra pods, apples, rose hips and almost anything we refer to as "seed pods" all actually are the fruit of various plants. For fruit to be produced, a plant has to carry out its reproductive efforts successfully.
The parts that make up flowers can vary greatly from one type of plant to another. The basic plan includes male and female parts in the same flower along with nonsexual parts such as petals.
The stamens, which are the male parts, produce pollen that carries the male germ cell or sperm. The female parts, called the pistil, hold the ovules or eggs.
When pollen is transferred to the pistil of a suitable flower, pollination takes place. If all goes well, this leads to the fertilization of the eggs by the male germ cells. The growing embryos form within seeds and stimulate the development of the surrounding ovary into the fruit. (Admittedly, in a few kinds of plants, seedless fruit is produced without fertilization).
That sounds simple enough; so what could possibly go wrong?
For one, weather conditions can interfere. Temperature extremes can cause the pollen of some plants to lose viability and thus prevent pollination. For example, that’s why tomatoes produce little fruit in mid summer. Fruit trees that bloom over a relatively short period of time, such as peaches, apples and pears, can suffer loss of production if the weather is bad while they are blooming– not to mention how devastating a late freeze during blooming could be.
When growing fruit trees, you also must know which are self-pollinating and which are self-sterile. Apples, pears and plums are self-sterile, meaning that the pollen a plant produces will not fertilize its own eggs. Pollen from a different cultivar of the same kind of fruit tree must be transferred to the flowers (cross-pollination) for fruit to form.
Certain types of plants produce some flowers that have only male parts (staminate flowers) and some that have only female parts (pistillate flowers). For these plants, only the female flowers on the plant actually will form the fruit. Cucumbers are a good example. I often hear from a distressed gardener concerned that most of the flowers are falling off without making cucumbers. Knowing that they are male flowers relieves the stress.
So some plants produce flowers with both male and female parts, and some produce separate male flowers and female flowers on the same plant. Have plants taken the next step, and are there species that produce some plants with all male flowers and some plants with all female flowers? The answer is, yes. Hollies, swamp red maples, papayas and date palms are just few of the plants that bloom that way.
These plants have adopted a sexual reproductive strategy used almost universally by animals. There are male and female members of the species. Male and female plants of the same species appear identical except for one great difference – only the females bear fruit.
That means if you want a holly that will produce red berries, it has to be a female. If you want a swamp red maple that will produce the wonderful burgundy fruit in the spring, it has to be a female. The only sure way to know you are getting a female is to choose a plant that has fruit on it, or a named variety that is a female clone, such as the Savannah holly.
So keep in mind, whenever you are growing a plant that you expect to produce fruit, the more you know about its reproductive habits, the more successful you are likely to be.
Get It Growing is a weekly feature on home lawn and garden topics prepared by experts in the LSU AgCenter. For more information on such topics, contact your parish LSU AgCenter Extension office or visit our Web site at www.lsuagcenter.com. A wide range of publications and a variety of other resources are available.