Flowering Habit and Production of Seeds

VICTOR R. BOSWELL.

AMATEUR GARDENERS sometimes ask, "What should I do to get seeds of the plants that I grow in my garden?"

We could give almost as many answers to that question as there are kinds of plants in the inquirer's garden. If one's interest in the question goes beyond the garden to the field, orchard, and forest, we would have to give additional answers.

Before we can answer the question about any plant we must know a good many intimate things about it. The procedure for obtaining "good" seeds of a particular plant is determined by several of its major and most obvious characteristics.

First, we need to know whether the plant is an annual, a biennial, or a perennial one and how long it takes to grow from seed to seed.

We also need to know the nature of its sex expression. Does it produce flowers containing functional organs of both sexes? Are the flowers normally self-fertilized, or are they cross-fertilized? Are the sexes borne in different flowers, and where are the different flowers on the same plants or on different plants? How are the flowers pollinated?

Our point of view in this chapter is that of the purposeful producer of seed rather than that of the incidental "saver" of a few seeds.

Plants that can grow from seed to seed in one season the annuals are easier to grow than those that require two seasons (biennials) or more (the perennials).

Some plants that are perennial in the Tropics, such as cotton, castor-bean, tomato, and lima bean, complete a reproductive cycle (from planted seed to production of mature seed) within one season in a temperate climate. Bad weather then kills them; these perennials thus behave like annuals in the United States.

Conversely, such annuals as spinach, lettuce, wheat, and cornflower (Centaurea cyanus) are hardy enough to go through mild winters in a vegetative state, following planting in autumn. Cold or short days, or both, prevent flowering until spring. These annuals thus may be treated as biennials.

Annuals generally flower in a few weeks to 2 or 3 months after growth starts in the spring. Mature seeds develop in another 2 to 6 weeks. The times differ among species and varieties and depend on the temperature. The time of flowering of many species also depends largely on the length of day.

Some annuals, such as garden peas, tend to mature so fast during hot weather that they flower, produce seed, and die before they develop a plant large enough to yield a large crop of seeds.

Some other annuals tolerate hot weather but are sensitive to daylength. They will flower and form seeds when an effective daylength occurs even though the plants are still young and small. The Biloxi soybean and the cocklebur (Xanthium) are examples.

Spinach and some other annuals are sensitive to both heat and daylength. They "shoot to seed" during warm, long days much too soon to have formed a plant of highly productive size.

All the species that are sensitive to heat or daylength must be planted early in the spring if the plants are to grow large enough to yield well.

Hardy species, including the so-called winter legumes, the winter grains, and certain vegetables, such as spinach, are most productive of seeds in regions of mild to moderate winters when they are planted in the autumn so as to produce seeds the following spring or summer.

Many cultivated annuals present no special problems of adjustment to daylength or to the normal range of growing-season temperatures, once their requirements are known. Among them are various beans grown for food, other legumes grown for forage, annual oilseed and fiber crops, and the grain crops.

The fruit-bearing vegetables, such as tomatoes, peppers, the vine crops melons, cucumbers, squash; and okra, also are in this group. Reasonably early planting ' of all of them encourages the development of larger plants, more flowers, and better yields of seed than late plantings do, other things being the same.

BIENNIAL PLANTS present more difficulties for the seed producer than annuals or perennials do.

Biennials produce only a vegetative phase of the mother plant in the first season. They flower, produce seed, and die in the second season.

Some plants, such as the true clovers (Trifolium), are actually perennials but generally they become relatively unproductive after they produce their first seed crop, in their second year.

They are therefore usually plowed under after their second year. Producing seed of sugarbeets and biennial vegetables is troublesome and costly. It is sometimes feasible to leave the mother roots or plants (such as cabbage and celery) in place where they grow the first season and to harvest commercial seed from them the next season without disturbing them over winter. If the winters are too severe, however, it is necessary to remove the mother plants (or their bulbs or storage roots) of many species from the field in the autumn for artificial protection and to plant them back the following spring.

If mother roots or bulbs are to be selected for good type, they must be harvested and selected in the autumn and stored over winter. It is wise to reselect them for good storage behavior when they are removed from storage in the spring and before they are planted in the seed field.

In the second season, the flowers of biennial vegetables develop on a strong stalk that arises from the apex of the stem within a bulb, atop a root, or within a rosette of leaves. Stalks also may arise from strong lateral buds, especially if the apex has been injured. The flower stalk generally begins to develop deep within the mother structure during early winter to midwinter. The flower parts, too, start development in many species during midwinter to late winter, completely out of sight.

Whether a flower stalk will form, when it will emerge, and how prolific it will be all depend on the interplay of several factors.

For a good yield of seed, the mother plant must have developed to the required size and physiological state in its first season. It must go through a requisite period of low temperature, not too cold but just cool enough. One to two months at 40 to 50 F. is effective for most biennial crops.

The weather must be moderate when the mother structure resumes visible growth. The daily mean temperatures should not be much over 70 . Freezing of the tissues at any time does not help induce floral development but may hinder it. Long days in the second season favor flowering in beets and some other species.

Species and even varieties within species differ in their requirements and in their responses to these several factors. Flowering and seed production are generally satisfactory when mother plants have been grown to market stage (or nearly so) and then allowed to go through a winter cold enough to keep them from growing but not cold enough to damage them visibly.

Production difficulties of various kinds are most likely to be encountered in sections where the winter gets so cold that artificial storage is necessary or is so mild that flower stalks fail to form. Planting the mother crop too late the first season may mean failure of floral induction. Planting too early or too late may mean winter injury.

Storing mother bulbs or roots near the freezing point from autumn harvest to spring planting will largely or entirely prevent floral initiation during storage and it may prevent flowering and seed production in the second season.

Hot weather immediately after the emergence of flower stalks can interrupt floral development and cause a resumption of vegetative growth in such plants as beet and cabbage. It may cause sparse or abnormal development of flowers. If the days are long enough, however, the adverse effects of high temperature are less serious on long-day seeders, like the beet, than if high temperature occurs during shorter days.

To avoid the high costs of harvesting, storing, and planting mother bulbs, roots, and plants, seedsmen sometimes produce seed of a biennial plant by the seed-to-seed method. They leave the mother plants in place to go to seed the second season. Because they thus have no opportunity to rogue out off-type bulbs or roots, they must maintain strict control of type and uniformity through the stock seed to assure satisfactory quality of the commercial seed.

Cabbage is produced seed-to-seed by sowing stock seed in late summer and letting the plants go through the winter in the rosette stage and shoot to seed in the spring without ever forming heads.

Cabbage seed also can be grown from the stumps of selected plants from which typical heads have been harvested, without moving the stumps. The practice is feasible only in regions of mild winters and with stumps of a crop harvested in autumn or winter.

Most of these biennials flower from early to late spring and produce mature seed from midsummer to late summer, depending on the species and the climate where each is grown.

THE REQUIREMENTS for flowering and the times of flowering of perennials are no less diverse than those of annuals and biennials.

Many perennial grasses and most of our forest and fruit trees flower early in the spring. Some perennial grasses, such as sugarcane, and trees and shrubs, such as filbert (Corylus americans) and Osmanthus, flower in late autumn to early spring. Perennials of some kind or another can be found in bloom all through the growing season.

The seeds in many perennial grasses and herbaceous ornamentals mature 2 to 3 weeks after bloom. They must be harvested promptly before they fall from the plant and are lost.

Some perennials, such as hollyhock, produce flowers and seeds successively over many weeks, and the seeds must be harvested repeatedly lest they be lost. Others, such as asparagus, hold their fruits firmly until autumn harvest, although they flower and form fruits over many weeks.

Most of the cultivated, herbaceous, seed-bearing perennials begin flowering and producing seed a year or two after they are grown from seed. One, the ornamental "century plant" (Agave americans), takes 10, 20, even 50 years or more to flower.

Seeds of some fruit trees are required for growing rootstocks, and seeds of forest trees for planting in nurseries of ornamental, windbreak, and timber trees.