Horticulture Principles and Practices

9.7 PURCHASING SEED
Select seed cultivars that are adapted to your locality. Extension agents can assist you in
making the right choice. Select fresh seeds if possible, and have them ready to plant on
time. Seeds should be purchased from a reputable grower or store. The date of harvest is
usually printed on the seed packet. Mail-order purchases are available through a variety
of outlets. Seed companies produce seed catalogs on an annual basis. Some small seed
companies may provide seed at a lower cost to growers. However, more established
companies provide a variety of information on the seed packet to guide the grower with
limited knowledge about growing plants.
9.8 SEED COMPANIES
The seed industry was introduced in Chapter 1. The seed market is very lucrative
worldwide. There are numerous small seed producers, some specializing in vegetables,
specialty crops, and ornamentals. Being a lucrative area, mergers and acquisitions have
characterized the seed industry in the past two decades, some of the recent shuffling
including the acquisition of Novartis by Monsanto in 2005, and prior to that Syngenta
(formerly Novartis/Astra Zeneca), Pioneer incorporating Dupont, and the merger of
Monsanto and Pharmacia. These behind-the-scene corporate maneuverings notwithstanding,
growers of horticultural crops deal with the smaller seed companies that
specialize in their crop or plant species of interest.
9.9 SEED DORMANCY
Seed Dormancy
The failure of viable seed
to germinate under
adequate environmental
conditions.
All seeds do not germinate, even when optimal conditions are provided. A physiological
or structural adaptive mechanism called dormancy imposes further restrictions on the
requirements for germination. Seeds germinate only after the dormancy is overcome or
broken. Dormancy is desired in the wild, where plants depend entirely on nature for survival.
It prevents germination in the face of adverse weather, which will kill the vulnerable
seedlings after emergence. Structural dormancy is imposed via the seed coat
(seed coat dormancy) (e.g., Camellia and redbud). Hard seed coats are impermeable to
the much needed moisture that is critical for germination. The seed coat may be softened
before planting by one of several methods, such as scarification, a method of mechanically
scratching the seed coat (by, for example, tumbling seeds in a drum containing
coarse material). Seeds may also be scarified by soaking them in concentrated sulfuric
acid or household bleach for a period.
Physiological dormancy (embryo dormancy) occurs when the embryo requires a
special treatment to induce it to start active growth. A cold temperature application
(called stratification) of about 1 to 7°C (34 to 45°F) is commonly required to break the
dormancy. Woody species like holly (Ilex spp.) and magnolia (Magnolia grandiflora)
require this treatment. Seed to be stratified is soaked in water for about twelve to twentyfour
hours prior to placement in a sterile medium container such as a polyethylene bag
to hold in moisture. The medium should permit good aeration to occur. Effective media
include coarse vermiculite, sphagnum moss, coarse sand, or a mixture of equal volumes
of peat and perlite. Seed may be wrapped in cheese cloth prior to placement in the
medium to eliminate the need for cleaning the seed after the treatment. Stratification in
the fridge takes about three to four months to complete.
A number of chemicals in plants inhibit germination of seeds while they are still
embedded in the pulp of the fruit (e.g., in tomato and strawberry). In some species, such
as Pinus and Ranunculus, the fruits are shed before the embryo fully matures. Such
296 Chapter 9 Sexual Propagation