chapter 19
               Plant Propagation
                 UW-EXTENSION MASTER GARDENER MANUAL: FOUNDATIONS IN HORTICULTURE
                                                           Introduction                                 Plant breeding 
                                                                        any gardeners plant seed        The terms “plant breeding” and 
                 In a nutshell…                                         in the ground and watch         “genetic engineering” are often 
                 •  Propagating plants is a fun way                     it grow. Others browse          confused. Both are methods of 
                    to create new plants.                  Mthe garden center for                       developing new plants with desirable 
                 •  You have to think about plants         varieties of plants with little thought      characteristics. Genetic engineering is 
                    in a different way if you plan on      to where they came from. Some divide  essentially a type of breeding. 
                    saving seeds.                          plants in their gardens to improve           Plant breeding has been practiced 
                                                           vigor or to share with a neighbor. In        for thousands of years. It involves 
                 •  We’re talking plant sex: You           studying plant propagation you will          pollinating the flowers of a chosen 
                    need to understand how                 learn how to affect a plant’s growth by      plant with pollen from another 
                    plants reproduce to be able to         manipulating environmental growing           chosen plant, both with desirable 
                    effectively propagate them.            conditions, resulting in more plants.        characteristics. The seeds produced 
                 •  For issues not covered in this         In gardening, plant propagation refers       are then planted and the resulting 
                    chapter, contact your county           to the many ways of starting new             plants are evaluated for their quality. 
                    Extension office:                      plants. These various processes of           Promising plants are “selected” for 
                    counties.uwex.edu                      multiplying or perpetuating a plant          their desirable characteristics or to be 
                                                           species may be by natural or artificial      used for further breeding. With plant 
                                                           means. This chapter introduces               breeding, the same pollination could 
                                                           concepts and techniques for growing          theoretically occur naturally; human 
                                                           new plants from seed and by asexual          involvement directs which two plants 
                                                           methods.                                     are combined.
                                                           Learning                                     Genetic engineering is a relatively new 
                                                                                                        technology that involves manually 
                                                           objectives                                   inserting the DNA from one organism 
                                                                                                        into the cells of another. In some 
                                                              Understand the biology involved in        cases, the gene inserted into a plant 
                                                          1plant propagation.                           is not from another plant, but from 
                                                               Know the conditions for starting         a different organism altogether. 
                                                           2seeds.                                      For example, Bacillus thuringiensis 
                                                               Demonstrate techniques for               is a bacterium whose DNA is often 
                                                           3asexual propagation.                        inserted into plants to provide pest 
                                                                                                        control. Genetic engineering involves 
                                                                                                        a recombination of genes that could 
                                                                                                        not occur in nature without human 
                                                                                                        involvement.
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          UW-Extension Master Gardener Manual: Foundations in Horticulture
                                      Patents, trademarks, and trade                         Propagation basics
                                      names                                                  Plants can be propagated in two main ways: 
                                      Plants developed through traditional breeding          sexually and asexually. Sexual propagation 
                                      or genetic engineering have a unique, desirable        is the recombination of plant genetic material 
                                      characteristic that can be patented by the             to form a genetically unique individual. This 
                                      government. A patent gives the recipient               generally involves the floral parts of a plant, 
                                      the right to exclude others from asexually             pollination that results in the formation of seeds, 
                                      reproducing, selling, or using the plant for a set     and starting plants from seed.
                                      time, usually 20 years. Patent holders can sell        Asexual propagation produces new plants 
                                      licenses to producers who are authorized to            that are genetically identical to the parent plant 
                                      propagate the plant, and it is illegal for those       by taking a vegetative part of the parent plant 
                                      without a license to reproduce and sell the plant.     (stems, roots, leaves, or other non-reproductive 
                                      Of the hundreds of thousands of plants available,      plant parts) and causing it to regenerate into a 
                                      only a small number of them are patented. For          new plant.
                                      a plant to be patented, it must be distinctly 
                                      different from existing cultivars. Patents are not     Sexual propagation: 
                                      awarded for plants found in the wild.                  from seeds
                                      Trademarks are words, acronyms, phrases, logos, 
                                      or symbols that identify the source or origin of       Propagation by seed is a common method of 
                                      a plant or type of plants. A trademark does not        producing new plants. Sexual propagation may be 
                                      give exclusive rights to the plant as a patent does,  cheaper and quicker than other methods, and it is 
                                      but it prevents others from using the trademark.       a way to obtain new cultivars and hybrid vigor. 
                                      Trade names identify a company name, but do            Seed propagation results in a lot of genetic 
                                      not specifically identify a plant or product.          variability, so offspring may not have the exact 
                                                                                             characteristics of the parent plant. Seedling 
                                                                                             variation is quite high in some plants; many 
                                                                                             ornamental plants do not come “true” from 
                                                                                             seed. Other plants are more true to type. Many 
                 All-America selections                                                      vegetables and annual flowers are easily grown 
                 All-America Selections (AAS) is a non-profit                                from seed. Some perennials can also be grown 
                 organization that tests and introduces                                      from seed, but may not flower the first season.
                 significantly improved new flowers,                                         Pollination and fertilization
                 bedding plants, and vegetables grown                                        Pollination and fertilization are processes that 
                 from seed. AAS tests are conducted at trial                                 result in the formation of new seeds. 
                 grounds throughout North America with                                       •  Pollination is transfer of pollen to the female 
                 official AAS judges supervising the trial and                                  flower parts by wind or pollinators, such as 
                 evaluating each entry. AAS Winners have                                        bees or other insects. 
                 been tested for home garden performance                                     •  Fertilization is the union of the male and 
                 and are quite reliable because of these                                        female reproductive material. 
                 unbiased, independent tests. AAS Display 
                 Gardens in the U.S. and Canada are open                                     •  The stamen is the male portion of the flower 
                 to the public to provide gardeners with                                        that produces the pollen. 
                 opportunities to view the most recent AAS                                   •  The dust-like pollen is contained in the 
                 Winners.                                                                       anthers, the sacs at the end of the filament. 
                                                                                             •  The typical female pistil consists of an enlarged 
                                                                                                ovary (containing the egg) at the base, a 
                                                                                                columnar style and the stigma, the organ that 
                                                                                                receives the pollen on the end. 
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                                                                      PLANT PROPAGATION
           When pollen grains land or are placed on the        The embryo is a new plant resulting from the              chapt
           stigma, they germinate to form a pollen tube that   union of pollen and egg during fertilization. 
           grows down the style to the ovary, allowing the     Cotyledons, or seed leaves, are attached to the 
           male reproductive material to move to the egg       embryo. Monocotyledons (monocots), such 
           (figure 1). Once the male reproductive material     as grasses, have one cotyledon; dicotyledons 
           fertilizes the egg, seeds can be produced. To       (dicots), such as beans, have two cotyledons. 
           understand these processes, it is important to      A mature seed contains enough stored food (or 
           know the parts and functions of a flower (see       energy source) for seed germination and early 
           chapter 1, Botany).                                 seedling growth. The cotyledons of dicots usually 
           FIGURE 1. The parts and functions of a flower       contain this food reserve, while some seeds like          er 19
                 stamen                       pistil           monocots have a mass of food reserve called an 
                                                               endosperm. 
                                                               Seed coverings are the seed coat and parts of 
               anther                        stigma            the fruit or seed pod. These structures protect 
            filament                           style           the embryo and food reserve inside the seed and 
                                                               sometimes prevent germination until conditions 
                                                               are suitable.
                                                  ovary        Selective pollination
            petal                                              Four seed types can be produced by selectively 
                                                               pollinating plants with specific parents: inbred 
                                                               lines, F1 hybrids, F2 hybrids, and seed mixtures.
                                                               Inbred lines
                                                 sepal         Inbred lines are created when plants from a single 
                                                               parent line are self-pollinated or interpollinated 
           Anatomy of a seed                                   so they become nearly identical after several 
                                                               generations. These flowers or vegetables are 
           A seed is usually made up of three basic parts      often easier and faster to breed and produce. 
           (figure 2):                                         Common self-pollinated, non-hybrid, and 
           •  The embryo                                       purebred annuals and vegetables are suitable 
           •  A food supply                                    candidates for saving seed. 
           •  The outer protective covering                    •  Some vegetable seeds that can be easily 
                                                                 saved include lettuce, beans, peas, herbs, and 
           FIGURE 2. Anatomy of a seed                           heirloom tomatoes. 
                                                               •  Annual flower seeds that can often be 
                                plumula                          successfully saved include cleome, salvia, and 
                                hypocotyl     embryo             nicotiana.
                                radical
                                micropyle
                                cotyledon
                                seed coat
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                                      F1 hybrids                                               Seed saving
                                      F1 hybrids are created by crossing two inbred            Seed left over in a package after planting can be 
                                      parent plants—often that differ in several               saved for next year’s garden, usually with little 
                                      important traits—resulting in uniform, often very        loss in germination, if stored properly (see “seed 
                                      prolific plants. Control of the cross-pollination of     storage”). 
                                      these plants is critical for hybrid seed production.     You may also choose to save seed from plants 
                                      These crosses are made to develop qualities like         you grow in your garden from one year to the 
                                      good vigor, heavy yields, uniformity, disease            next. Saved seed may not produce plants that are 
                                      resistance, and other desirable traits. Hybrids          the same as the parent plant. Cross-pollination 
                                      are often more vigorous than either parent,              in some crops may result in altered genetic 
                                      but cannot breed true. Seeds collected from F1           characteristics, so new plants grown from these 
                                      hybrids will not produce plants identical to those       seeds might have any combination of new 
                                      from which they were collected.                          characteristics, such as fruit size, blossom color, 
                                      F2 hybrids                                               shape, or flavor. Some vegetables that are self-
                                      F2 hybrids are the result of self-pollination or         pollinated and therefore are good seed-saving 
                                      indiscriminate pollination of F1 hybrids. These          bets include beans, eggplant, peas, and tomato.
                                      plants are more variable than the original hybrid        Seed storage
                                      but may maintain some of the characteristics of          It is important to store seeds properly to maintain 
                                      their parents. Plants grown from seed saved from         their viability. Seed is a living product that, once 
                                      F2 hybrids can be variable and unpredictable.            harvested, is constantly in decline. The storage 
                                      Seed mixtures                                            life of seed depends on both environmental 
                                      Seed mixtures contain seeds collected from               conditions and the plant species. Most flower and 
                                      plants—generally flowers—that vary only in a             vegetable seeds will keep for one year without 
                                      single trait, such as color. Field grown mixtures        special protection, and many will remain viable 
                                      come from plants of different colors growing             for up to 5 years if stored properly (table 1). The 
                                      together, which can result in slightly variable and      best conditions for seed storage are just the 
                                      unpredictable color mixtures. Formula mixtures           opposite of those required for germination—
                                      blend seed in predetermined proportions                  cool, dark, and dry.
                                      from plants of different colors that were grown          In general, the drier the seeds, the longer they 
                                      separately to produce a constant and predictable         will last. A relative humidity of 30% is ideal. The 
                                      balance of colors.                                       highly variable environment in the average 
                                      Obtaining seeds                                          home allows far too much (or too little) moisture 
                                                                                               exchange for long-term storage in paper 
                                      Seed selection                                           envelopes, cloth bags, or cardboard boxes. Place 
                                      Purchase good quality seed from reputable seed           seeds in an airtight container such as tight-
                                      companies that produce seed with controlled              sealing glass jars or resealable plastic bags. To 
                                      genetics and store seed properly.                        help reduce moisture in the container, you can 
                                      TABLE 1. Storage life of flower and vegetable seeds
                                        LONG-LIVED SEEDS                    MEDIUM-LIVED SEEDS                  SHORT-LIVED SEEDS  
                                        (5 OR MORE YEARS)                   (UP TO 5 YEARS)                     (1 TO 2 YEARS)
                                       beets, broccoli, Brussels sprouts,   basil, beans, calendula, carrot,    alyssum, aster, blanketflower, 
                                       cabbage, cauliflower, cilantro,      celery, chard, dianthus, dill,      coleus, corn, cosmos, delphinium, 
                                       cucumber, lavender, lettuce,         eggplant, forget-me-not, lupine,    leek, onion, pansy, parsnip, phlox, 
                                       melons, mustard greens, oregano,     marigold, nasturtium, parsley,      spinach, strawflower
                                       peppers, radish, sunflower, tomato,  peas, pumpkin, sage, snapdragon, 
                                       turnip                               squash, sweet pea, thyme, zinnia
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