It results in propagation of those plants which do not produce viable seeds or produce seeds with prolonged period of dormancy. (iv) The plants generated from vegetative means are more uniform and genetically similar to the parent stock.
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Plant propagation is the process of creating new plants. There are two types of propagation: sexual and asexual. Sexual reproduction is the union of the pollen and egg, drawing from the genes of two parents to create a new, third individual. Sexual propagation involves the floral parts of a plant. Asexual propagation involves taking a part of one parent plant and causing it to regenerate itself into a new plant. The resulting new plant is genetically identical its parent. Asexual propagation involves the vegetative parts of a plant: stems, roots, or leaves.
The advantages of sexual propagation are that it may be cheaper and quicker than other methods; it may be the only way to obtain new varieties and hybrid vigor; in certain species, it is the only viable method for propagation; and it is a way to avoid transmission of certain diseases. Asexual propagation has advantages, too. It may be easier and faster in some species; it may be the only way to perpetuate some cultivars; and it bypasses the juvenile characteristics of certain species.
Sexual Propagation
Sexual propagation involves the union of the pollen (male) with the egg (female) to produce a seed. The seed is made up of three parts: the outer seed coat, which protects the seed; the endosperm, which is a food reserve; and the embryo, which is the young plant itself. When a seed is mature and put in a favorable environment, it will germinate (begin active growth). In the following section, seed germination and transplanting of seeds will be discussed.
Approximate Life Expectancy of Vegetable Seeds Stored Under Favorable Conditions
Vegetable Years
Asparagus 3
Bean 3
Beet 4
Broccoli 3
Brussels sprouts 4
Cabbage 4
Carrot 3
Cauliflower 4
Celery 3
Chard, Swiss 4
Corn, sweet 2
Cucumber 5
Eggplant 4
Kale 4
Kohlrabi 3
Leek 2
Lettuce 6
Onion 1
Parsley 1
Parsnip 1
Pea 3
Pepper 2
Pumpkin 4
Radish 5
Rutabaga 4
Spinach 3
Squash 4
Tomato 4
Turnip 4
Watermelon 4
Adapted from J.F. Harrington and P.A. Minges, Vegetable Seed Germination, University of California Agricultural Extension Leaflet, unnumbered (1954)
Soil Temperature Conditions for Vegetable Seed Germination¹
Vegetable Optimum Range (°F)
Asparagus 60-85
Bean 60-85
Bean, lima 65-85
Beet 50-85
Cabbage 45-95
Carrot 45-85
Cauliflower 45-85
Celery 60-70
Chard, Swiss 50-85
Corn 60-95
Cucumber 60-95
Eggplant 75-90
Lettuce 40-80
Muskmelon 75-95
Okra 70-95
Onion 50-95
Parsley 50-85
Parsnip 50-70
Pea 40-75
Pepper 65-95
Pumpkin 70-90
Radish 45-90
Spinach 45-75
Squash 45-75
Tomato 60-85
Turnip 60-105
Watermelon 70-95
¹ Compiled by J.F Harrington, Department of Vegetable Crops, University of California, Davis.
² Daily fluctuation to 60°F or lower at night is essential.
Seed
To obtain quality plants, start with good quality seed from a reliable dealer. Select varieties to provide the size, color, and habit of growth desired. Choose varieties adapted to your area which will reach maturity before an early frost. Many new vegetable and flower varieties are hybrids, which cost a little more than open pollinated types. However, hybrid plants usually have more vigor, more uniformity, and better production than non-hybrids and sometimes have specific disease resistance or other unique cultural characteristics.
Although some seeds will keep for several years if stored properly, it is advisable to purchase only enough seed for the current year’s use. Quality seed will not contain seed of any other crop, weeds, seeds, or other debris. Printing on the seed packet usually indicates essential information about the variety, the year for which the seeds were packaged, and germination percentage you may typically expect, and notes about any chemical seed treatment. If seeds are obtained well in advance of the actual sowing date or are stored surplus seeds, keep them in a cool, dry place. Laminated foil packets help ensure dry storage. Paper packets are best kept in tightly closed containers and maintained around 40◦F. in a low humidity. The door shelves in a refrigerator work well.
Some gardeners save seed from their own gardens; however, such seed is the result of random pollination by insects or other natural agents, and may not produce plants typical of the parents. This is especially true of the many hybrid varieties. See UMaine Extension Bulletin #2750 for information on how to save your own seed.
Germination
Germination will begin when certain internal requirements have been met. A seed must have a mature embryo, contain a large enough endosperm to sustain the embryo during germination, and contain sufficient hormones to initiate the process. In general, do not expect more than 65% to 80% of new seeds to germinate. From those germinating, expect about 60% to 75% to produce satisfactory, vigorous, sturdy seedlings. There are four environmental factors which affect germination: water, oxygen, light, and heat.
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