B. Secondary
Viable seeds of many woody species may not germinate for considerable lengths of time, even when con-
ditions are ideal. This dormancy condition prevents seeds in their natural habitat from germinating in un-
seasonal times. Readily germinable seeds should be stored promptly and properly until sown. This usu-
ally requires keeping the seeds dry and storing them in a refrigerator in sealed plastic bags or other sealed
containers. In unseasonal times, seeds should be sown in a greenhouse or other favorable environment.
When the weather warms sufficiently, seedlings grown inside may be moved to a cold frame for further
growth [8].
VII. SEED TREATMENTS
The most simple and practical approach to overcoming seed dormancy is to sow in outdoor seed beds, al-
lowing nature and its seasonal cycles to provide the appropriate conditions. Cultural practices, including
good seed bed preparation, appropriate seeding rate and depth, and protection from pests, are all-impor-
tant factors for success [8]. Seedlings are usually allowed to grow from one to two seasons in beds or con-
tainers and then transplanted to more permanent field locations or to larger containers [8]. However, good
cultural practices may not always be reliable or successful.
Because of numerous interactions of the seed’s heredity expression and the effect of environmental
and other internal factors of the seed, the germination of different kinds of seeds, or even of different seeds
of one kind, can be extremely variable [20].
Treatment of seeds may hasten or induce more uniform and greater germination. It is more often re-
quired with seeds of woody trees and shrubs than with those of herbaceous species. Rudolf [26] found
that out of 400 species of woody plants, 33% had seeds that are commonly nondormant, 43% had seeds
with internal dormancy, 7% had seeds with an impermeable seed coat, and 17% had more than one kind
of seed dormancy.
Without treatment, dormant seeds of many woody species may not germinate or may do so sporad-
ically over a prolonged period lasting 2 or 3 years, resulting in plants of irregular size and age in seed beds
or flats. Treatment procedures usually involve one of two types: scarificationorstratification. A combi-
nation of both procedures may be required for seeds with more complex dormancy (Tables 2 and 3).
A. Scarification
Scarification is any treatment applied to seed to enhance germination [41].
- Abrasion
Hard seed coats can be scratched or abraded with a file, sandpaper, or abrasive wheel or cracked with a
hammer or vise grip. A small mechanical tumbler lined with sandpaper or filled with sand or gravel may
be more practical for larger amounts of seed [42]. The quantity of seeds in the tumbler should be suffi-
cient to allow all the seeds to be abraded. For very large quantities of seeds, a concrete mixer containing
coarse sand or gravel may be quite effective. The sand or gravel must be a size that can be easily screened
from the seeds [42].
Commercially designed machines are also available for scarifying large quantities of seed. These
scarifiers usually abrade or scar the seeds between two rubber-faced surfaces or impel seeds against
roughened surfaces such as sandpaper. The severity of the abrasion or impact must be controlled to pre-
vent damage to the seed [34].
- Acid
Concentrated sulfuric acid (H 2 SO 4 commercial grade, specific gravity 1.84) is often used because it is
very effective. Caution is advised when using acid. NEVER ADD WATER TO ACID! Goggles and pro-
tective clothing should be worn. Care must be taken to avoid spilling. Skin that comes in contact with acid
must be washed immediately under running cold water.
Using about twice the volume of acid over the seed in a glass container, stir gently with a glass rod
during treatment. Duration of acid exposure will depend upon seed coat thickness. Fifteen minutes to 3
hr or more of exposure is required, depending on the species. Carefully pour off the acid and rinse seeds
GERMINATION AND EMERGENCE 63