Seed quality at planting time pertains to a seed’s ability to germinate, develop a normal root and shoot and emerge through the seed bed without deleterious effects to the developing seedling. Here’s the bottom line, planting high quality seed will typically result in good stand establishment in your garden plot.
While you are in the process of purchasing planting seed, make sure that seed was harvested and processed in the season immediately preceding the season you are planning for. Also, check the packet for the seed’s anticipated germination rate. The germination information allows for the gardener to estimate the seeding rate. However, when seed germination is reported as <75%, it’s an indication that overall quality and vigor of the seed has dropped. In other words, 75% of the seed may germinate (by definition) but will the seed have enough food reserves to permit the seedling to emerge through the seedbed? If you are saving your own seed from last season, be sure to perform a seed germination test before planting.
SEED GERMINATION and SEEDLING EMERGENCE
There are basically two sequential events that take place once seed are placed in a moist seedbed. The first event is seed hydration. When the exterior surface of the seed comes in contact with soil moisture, water is attracted to the seed surface as well as to other water molecules. In a sense, the seed becomes encapsulated in a water like shell. After being fully hydrated (approx. 1 – 3 days) the seed will begin to absorb soil moisture into the seed’s interior. The seed then begins to swell, food reserves found within the endosperm (food storage tissue) become available to the developing seedling and many physiological processes (metabolic activity) are activated. Shortly thereafter, rapid development and elongation of the seedling’s shoot and root occur. In the garden, we typically experience germination and emergence taking between 4 to 14 days depending on the type seed and plant species.
To clarify an important point, please allow me to elaborate. The seed’s endosperm and embryonic plant are formed within the ovary (female flower) following pollination and fertilization of the female flower. Pretty cool, huh?
MONOCOTS and DICOTS
In the plant kingdom, there are two basic plant types in regard to how seed food reserves are stored, the number of embryonic leaves present, seedling emergence and the eventual root system. Of course, this post will address each type in reference to typical garden vegetables. Just so you know, there an estimated 60,000 species of monocots!!
Examples of Monocots (monocotyledons) are rye, wheat and corn. The seed of these type plants store food reserves within the seed’s endosperm and cotyledon. During the emergence phase, the coleoptile (diagram) moves straight upward and penetrates the soil above. Soon afterward, the epicotyl (diagram) emerges from the coleoptile and gives rise to the plants first true leaves. Meanwhile, the root (radicle) begins to grow downward giving rise to a fibrous root system.
Examples of Dicots (dicotyledons) are bean, soybean and spinach. A dicot seed typically stores food reserves within the cotyledons. During the emergence phase, the stem (hypocotyl) is seen coming up through the seed bed in an arched position. It is preparing to lift the attached cotyledons and upper stem (diagram) through the seed bed. Although the cotyledons are short-lived, they will also produce photosynthate. The root grows downward giving rise to a branched and tap root system.
Should you have the desire to save seed from one year to the next, know that it is easily accomplished. Most vegetable seed will retain good vitality when stored under dry (low humidity) and moderate temperature (60F – 70F) conditions. I store my seed at home in a kitchen cupboard. Since my home is kept between 65F to 73F, all year longw, seed saving is doable. Even so, I don’t attempt to save seed once it has reached two years past it harvest or purchase date.
One last point, seed are alive! Even in a seed’s so-called dry state, they continue to respire at very low rates. Poor storage conditions will hasten respiration leading to a decline in the seed’s overall quality.
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