Overcoming seed dormancy : trees and shrubs

Department of Horticultural Science Horticulture Information Leaflet 8704 1/99 OVERCOMING SEED DORMANCY: TREES AND SHRUBS Erv Evans, Extension Associate, Horticultural Science Frank A. Blazich, Professor, Horticultural Science ■ Seed dormancy is nature’s way of setting a time clock that allows seeds to initiate germination when conditions are normally favorable for germination and survival of the seedings. For example, dogwoods produce mature seeds in the fall, but conditions are not suitable for seedling survival at that time. Thus, dogwoods have developed a mechanism that keeps the seeds dormant until spring when conditioas axe favorable for germination, as well as, seedling growth and survival. Viable seeds that do not germinate are said to be dormant. Dormancy can be regulated by the environment or by the seed itself. If a seed is not exposed to sufficient moisture, proper tempei'ature, oxygen, and for some species light, the seed will not germinate. In this case, the seed’s donnancy is due to unfavorable environmental conditions. On the other hand, some seeds may not germinate because of some inhibitory factor of the seed itself. This particular kind of donnancy consists of two general types: (a) seed coat or external dormancy and/or (b) internal (endogenous) donnancy. Distributed in furtherance of the Acts of Congress of May 8 and June 30, 1914. Employment and program opportunities are offered to all people regardless of race, color, national origin, sex, age, or disability. North Carolina State University, North Carolina A&T State University, U.S. Department of Agriculture, and local governments cooperating. Techniques to Break Dormancy Seed Scarification — Seed coat (external donnancy) results from a seed’ s hard seed coat that is impervious to water and gases. The seed will not genninate until the seed coat is altered physically. Any process of breaking, scratching, or mechanically altering the seed coat to make it penneable to water and gases is known as scarification. In nature, this often occurs by fall seeding. Freezing temperatures or microbial activities modify the seed coat during the winter. Scarification can also occur as seeds pass through the digestive tract of various animals. Scarification also can be forced rather than waiting for nature to alter the seed coats. Commercial growers scarify seeds by soaking them in concentrated sulfuric acid. Seeds are placed in a glass container and covered with sulfuric acid. The seeds are gently stirred and allowed to soak for lOminutes to several hours, depending on the species. Various reference books provide appropriate concentrations and durations of treatment. When the seed coat has been modified (thinned), the seeds are removed, washed, and sown. Sulfuric acid can, however, be very dangerous for an inexperienced individual and should be used with extreme caution! Vinegar is safer (but less effective treatment) and can be used for species that do not have an extremely hard seed coat; the technique is the same as with sulfuric acid. For mechanical scarification, seed coats can also be filed with a metal file, rubbed with sandpaper, nicked with a knife, or North Carolina Cooperative Extension Service NORTH CAROLINA STATE UNIVERSITY COLLEGEOFAGRICULTURE&LIFESCIENCES