Vegetable Seed Production
Vegetable seed technology
Although some vegetables like potatoes are vegetatively propagated,
most are established from seeds. Using quality seeds is a prerequisite
for successful vegetable production. Although many of the F-1 hybrid seeds
used today are more expensive than the open-pollinated seeds used in the
past, vegetable seeds are still a rather small investment compared to
other production costs.
It is generally unwise to cut costs by saving a few dollars on seeds
of a substandard cultivar or by purchasing lower quality seeds. Cutting
corners on seed costs will generally end up costing even more because
of lost revenues from lower yields. Like so many other areas of agriculture,
seed handling practices have changed dramatically over the years. For
generations, farmers saved their own vegetable seeds and maintained their
own cultivars. More recently, seeds were often obtained from local agricultural
retailers. Today, vegetable growers are faced with a wide array of seed
treatments and cultivars that may be purchased from sources around the
There are many companies that sell vegetable seeds. However, the number
of companies that actually grow their own seeds and develop new cultivars
has been steadily decreasing over the past 50 years. Like other industries,
the seed industry is rapidly becoming highly specialized.
For example, some companies specialize in retail sales. Of these companies,
there are those that specialize in the home garden trade and others who
deal with commercial growers. Some seed companies specialize in seed production
and cultivar development and do not retail the seeds they produce, while
other companies are involved in all aspects of the seed trade. Several
companies do not sell seeds but specialize in coating seeds produced by
other companies. Some companies specialize in specific crops such as the
Hollar Seed Company which only produces cucurbit seeds and wholesales
them to companies specializing in retail sales.
Many of the large vegetable seed companies are multinational. Very few
of these companies are privately owned. Many are owned by other large
multinational corporations. For example, Petoseed, Royal Sluis, Asgrow
vegetable seeds and several other seed companies are now all owned by
the Mexican Company, Seminis.
Seed Act specifies minimum standards for vegetable seed quality
and labeling. Each state also has a seed law that is similar to
the federal seed law. All vegetable seeds sold commercially must
meet standards for minimum germination percentage, be true-to-type, and
not exceed tolerances for inert matter. State seed laws may have additional
restrictions on noxious weed seed content and package labeling requirements.
germination tests used to verify viability are conducted under optimal
conditions for each species as specified by the Association of Official
Seed Analysts. >>
However, these tests provide little information about the vigor of seeds.
A simple definition of vigor would be the ability of the seeds
to germinate under stressful conditions. Unfortunately, there
are no minimum standards for seed vigor in either the state or federal
State Seed Labs
Each state has a lab that will test for viability, purity, and freedom
from noxious weed seeds. The Virginia State Seed lab is in Richmond. These
labs will also test seed samples from the public for a small fee. In most
cases, state and federal agencies monitor vegetable seed sales to ensure
that they conform to state and federal standards. Most prepackaged seeds
far exceed the minimum requirements established by the state and federal
seeds laws. For example, by the Virginia State Seed Law, tomato seeds
must have at least 75% germination to be sold in the state. Most tomato
seeds purchased commercially will have germination percentages of at least
Many states have seed certification programs. Certified seeds
are carefully monitored during production and are certified to be true-to-type,
of high germinability, and to contain low percentages of weed seeds and
inert matter. Generally, only agronomic crops are entered into
seed certification programs, however, vegetables may also be included
in the program. For example, California at one time certified the production
of 'Charleston Gray' watermelon seeds.
Untreated seeds are rarely used by commercial growers. Many growers
hybrid seeds >> that are more expensive than the open-pollinated
seeds used in the past.
Many growers are willing to pay more for treated seeds to insure the
best possible stand establishment.
- Pesticide applications are one of the more common
seed treatments used today. A light coating of fungicide is usually
applied to the seed surface. A brightly colored dye is sometimes added
as a reminder that a fungicide has been applied. Systemic insecticides
have also been used as a seed treatment for certain crops.
- Inoculation of legume seeds with rhizobium to improve
nitrogen fixation after germination is another common treatment.
and pelleting >> are two widely used seed treatments, particularly
with small-seeded species. Coated seeds have a thin layer of material
such as clay or diatomaceous earth added to make the seeds larger but
not to change the overall shape. Seeds are coated to make them easier
to handle, to deliver chemicals, to improve soil contact, or to inoculate
seeds with microbes The exact composition of coating material is a carefully
guarded secret by the companies who develop them. Pelleted seeds have
been coated until they are round. This makes seeds easier to handle
and plant, particularly when planters that utilize belts with prepunched
holes of a specific size are used. To make identification easier, coated
seeds are often color coded, so cultivars or types are not mixed at
planting. One successful pelleting treatment splits upon hydration and
does not pose a barrier to radicle growth or limit oxygen availability
to the seeds.
- Film coating is another recent innovation. Many
coating materials are very dusty. However, film coatings are made of
the same materials used by the pharmaceutical industry to coat pills.
These coatings are water soluble but dust free.
- Pregerminated seeds, particularly celery, have been
marketed by some companies in Europe. One company marketed pregerminated
celery seeds in the United States briefly during the mid-1980's,
but they are no longer sold in this country to my knowledge because
the are very perishable.
- Fertilizer treatments should not be applied to seeds,
such as legumes, that are sensitive to high salts. However, some seeds
are relatively tolerant of salts and additions of very small quantities
of fertilizer with low salt index can boost early seedling growth. Research
suggests that some matric priming materials, such as diatomaceous earth,
boost early seedling growth because mineral nutrients are absorbed by
seeds >> derived from tissue culture and coated in gelatinous
material have been developed but are expensive, difficult to ship, have
a short shelf-life, and are excessively variable for commercial use.
Current research has focused on developing synthetic seeds that are
desiccation tolerant and can be handled like other seeds. Although progress
has been made in developing desiccation tolerant synthetic seeds, it
is unlikely that they will be commercially available for many years.
- Primed seeds have been subjected to a controlled
hydration process followed by redrying. Generally, priming reduces the
time to germination and may improve the seed's ability to germinate
under temperature or moisture stress. Priming does not usually improve
the viability of poor quality seeds. Peppers, tomatoes, and lettuce
show a greater response to priming than some other types of seeds. Since
the seed law does not require that primed seeds be labeled, they seldom
are. Some seed companies advertise seeds as "vigorized" instead
of calling them primed.
sized seeds >> are often available and have been carefully
sorted so all seeds are the same size. Sized seeds often have greater
uniformity of germination. In many cases, large seeds are sold at a
premium, because they are often more vigorous and may produce more uniform
emergence. Some growers prefer sized seeds in order to get more uniform
placement when belt seeders are used. It is possible to buy seeds spaced
at a specific interval on tape. The tape is buried in the ground and
dissolves when wetted.
- "Seed tapes" are used mainly by home gardeners.
Seeds are imbedded in water soluble tape for ease of planting.
Seed Production and Storage
for propagation are generally grown in special production fields by
farmers who specialize in seed production. >>
longevity of seed storage is determined by seed moisture content and
- As a general rule, seed storage life decreases by half for every
5 degree C rise in temperature from 0 to 50 degree C, or for every 1%
increase in moisture content from 5 to 14%.
- Another helpful rule is that the % relative humidity + the
temperature in degrees F should be kept below 100 during seed storage.
- Seeds are hygroscopic and can gain or lose moisture from the air.
If seeds are stored at moisture contents greater than 18%, damage can
occur from heat buildup due to high respiration. Between 10 and 18%,
fungi and mold can grow on seeds. Between 9 and 14% moisture content,
insects may be active.
- For open storage, starchy seeds should be stored at less
than 12% moisture content, while oily seeds such as watermelon
should be maintained at moisture contents less than 9%. Sealed storage
requires moisture contents from 6 to 8%. In some seeds,
storage at less than 4% moisture content can be damaging
due to auto oxidation of lipids. Beans are more susceptible to mechanical
damage when dried to less than 10% moisture content. As a general rule,
the best moisture content for seed storage is about 5%.
For storage at home, temperatures should be low but not below freezing.
In some germplasm repositories, some seeds are now stored in liquid
nitrogen, but seed moisture must be low and carefully controlled to
protect the seeds from damage. Seeds stored properly in liquid nitrogen
should last indefinitely.
- To protect genetic resources, the USDA maintains collections of diverse
cultivars for mainy of the important crops grown in the United States
at the National
Center for Genetic Resources Preservation (NCGRP) - Pictures
>> in Fort Collins, Colorado, formerly called the National
Seed Storage Laboratory.
- Seeds are packaged in many types of containers.
- The best containers can be resealed to keep the moisture content
- Containers made of paper or cloth should be avoided, because they
do not prevent moisture uptake by the seeds, and they are more easily
broken than other materials.
- Small quantities of seed are often sold in packets.
- Foil or plastic, hermetically sealed packets are preferred because
they keep seed moisture content low.
- Self-sealing packets are easy to use and protect the seeds from changes
in moisture content.
quantities of seeds are often sold in metal cans. >> These
provide effective protection from rodents and moisture until opened.
Cans should be supplied with a resealable cap to protect the unused
- Large-seeded crops, such as beans or peas, are often shipped in bags.
Plastic bags are good, because they protect against changes in water
content. When seeds are packaged in cloth bags, they should be placed
in a cool dry place until use so they do not absorb moisture from the
- New cultivars are released by seed companies each year.
- Don't be unduly influenced by glossy pictures and extravagant
claims in a catalog!
- New cultivars should be trialed on a limited basis before an established
cultivar is replaced.
- Many states publish lists of recommended cultivars (the commercial
vegetable production guide for Virginia contains cultivar recommendations).
These are cultivars that have performed well in Virginia over a number
- The All-American Trials test newly released cultivars
from seed companies at a number of locations around the country. If
a cultivar is an All-American winner, it simply means that it has performed
well at a number of locations in the US. There is no assurance that
a new cultivar will be superior to existing cultivars until its performance
has been tested in your area.
Planting Seeds in the Field
Standards of Seed Purity and Germination
Seeds entering into interstate commerce must meet the requirements
of the Federal Seed Act. Most state seed laws conform to the
federal standards. The kinds of primary noxious weeds, sometimes subject
to tolerances, and the secondary noxious weeds listed by the laws of the
individual states differ to a considerable extent. The weed seed regulations
and the tolerances allowed, if any, may be ascertained by contacting the
State Seed Laboratory of any state.
Each container of vegetable seeds must contain or have attached
to it a label that gives the following information:
- Name of kind, variety, or hybrid of the seed. The representation
of kind and variety shall be confined to the recognized name of the
kind and variety. It shall not have affixed thereto words or terms that
create a misleading impression about the history or characteristics
of the kind of variety.
- Full name and address of the person who transports the seed in interstate
commerce or the person to whom the seed is shipped.
- Germination information:
- Percentage of germination, exclusive of hard seed.
- Percentage of hard seed, if present.
- Date of test.
- Statement as to any seed treatment including the name of substance
Small packets of seed for home garden use are not required to meet these
labeling requirements in some states.
The Reproductive Characteristics of Some Common Vegetables
Please refer to this handy reference table
summarizing the reproductive characteristics of many of the important
vegetables we will discuss in detail later in the class. Don't
attempt to memorize this information now, will discuss the detailed life
cycle of each crop separately. At this time please note the various strategies
different vegetables use to reproduce.