Understanding how seeds germinate and grow into healthy seedlings is critical for successful crop establishment. This is a brief summary of seed and seedling biology and recommendations for producing healthy seedlings. Few decisions are more important to successful vegetable production than choosing the right seed. Seeds should be of high quality, clean, and purchased from a reputable seed company. Take care to choose varieties that are well adapted to the area, and suit local consumer preferences.
Certified organic growers are required to use certified organic seed and seedlings with only a few exceptions. All fully developed seeds contain an embryo and, in most plant species, a store of food reserves, wrapped in a seed coat.
Seeds generally "wake up" and germinate when soil moisture and temperature conditions are favorable for them to grow. But not all seeds have the same germination requirements, so it is important to know what each seed type needs. Seeds need the proper temperature, moisture, air, and light conditions to germinate.
All seeds have optimal temperature ranges for germination Table 1. The minimum temperature is the lowest temperature at which seeds can germinate effectively. The maximum is the highest temperature at which seeds can germinate. Anything above or below this temperature can damage seeds or make them go into dormancy.
At optimal temperatures, germination is rapid and uniform. All seeds need both moisture and air to germinate. Good seed-to-soil contact is very important. A fine-textured seedbed with little compaction is recommended for direct seeding in the field.
For greenhouse transplants, soilless media should be moist and fluffy. The soil or growing media must contain enough moisture so that the seed can take up water to begin the germination process. But if the soil or media are too wet, or too compacted, there will not be enough air around the seed to "breathe". Like any other living organism, seeds need oxygen for respiration, and that oxygen comes from air in the soil. Not all seeds have the same light requirements.
Most seeds germinate best under dark conditions and might even be inhibited by light. A few other seeds need light to germinate. But once seeds have germinated and broken through the surface of the soil or growing media as seedlings, they all need sunlight to grow. Table 1 shows optimal soil temperatures for germination for common vegetable crops. When a dry seed comes into contact with moist soil or growing media, the seed begins to take up water through the seed coat.
As it takes up more water, the seed expands and the seed coat cracks open. The embryo inside the seed is made up of a small shoot and a small root. The root is the first to emerge from the seed. As it grows, it anchors the plant to the ground, and begins absorbing water through the root. After the root absorbs water, the shoot begins to emerge from the seed. Most of the vegetable plants that we grow are "dicots".
Dicots have two seed leaves in the shoot that emerge from the germinating seed. As the sun reaches up high in the sky, your cannabis will want to as well. Make sure all of your plants are outside by the Summer Solstice.
The weather will start to turn and the sun will begin descending in the sky as your plants fatten up with sweet, sticky buds. It might be tempting, but wait until around the Fall Equinox to start harvesting. Everything should be cleaned up, dried, and curing well before the Winter Solstice. Be sure to keep a grow journal to track the progress of your plants. Looking back on your notes will help you learn from mistakes and maximize the quality and quantity of your buds.
Take meticulous notes on when and how you perform each step, as well as what the weather is like. Other notes can include how much water you give plants, at what intervals, and how much nutrients you give them.
Pictures will also give you a better sense of how your plants look along the way. The first marijuana plant stage begins with the seed. A cannabis seed should feel hard and dry, and be light- to dark-brown in color. The tap root will drive down while the stem of the seedling will grow upward.
Two rounded cotyledon leaves will grow out from the stem as the plant unfolds from the protective casing of the seed. These initial leaves are responsible for taking in sunlight needed for the plant to become healthy and stable. As a sprout, the seed will initially produce leaves with only one ridged blade. Once new growth develops, the leaves will develop more blades 3, 5, 7, etc.
All seeds have optimal temperature ranges for germination Table 1. The minimum temperature is the lowest temperature at which seeds can germinate effectively. The maximum is the highest temperature at which seeds can germinate. Anything above or below this temperature can damage seeds or make them go into dormancy. At optimal temperatures, germination is rapid and uniform. All seeds need correct moisture to initiate internal processes leading up to germination.
In field soil this is generally about percent of field capacity. A fine-textured seedbed and good seed-to-soil contact are necessary for optimal germination. Aeration in the soil media allows for good gas exchange between the germinating embryo and the soil.
Seeds respire just like any other living organism. They need oxygen and produce carbon dioxide CO 2. This carbon dioxide needs to be able to move away from the seed. If the soil or media is not well aerated due to overwatering or compaction, the CO 2 will not dissipate and seeds can suffocate.
Not all seeds have the same light requirements. Most seeds germinate best under dark conditions and might even be inhibited by light e. However, some species e. Don't confuse seed light requirements with what seedlings need. All seedlings require sunlight. Seedlings will become leggy and fragile and will not produce to their potential if they do not have sufficient light.
Soil temperatures should be taken by inserting a soil thermometer inches deep into the soil surface and noting temperature. Adapted from Kemble and Musgrove Some viable seeds might not germinate.
Many seeds have developed a dormancy or sleep period. Seed dormancy is a condition that prevents germination even under optimal environmental conditions. Why would it benefit seeds to not all germinate when conditions are right? In nature, staggering germination keeps some seedlings safe from possible bursts of bad weather or herbivores that might eat them.
Seeds of plants that grow best in the spring have self-selected to germinate only after cold winter temperatures have passed. For seeds to come out of dormancy, we have to break their physical or chemical dormancy factors. Seeds might have a hard or thick seed coat physical dormancy.
This can be broken by soaking or scarifying scratching the surface the seed. Other seeds have internal chemical or metabolic conditions that prevent germination chemical dormancy. Factors affecting seed dormancy include the presence of certain plant hormones--notably, abscisic acid, which inhibits germination, and gibberellin, which ends seed dormancy. For example, the membrane within the seed coat of some seeds forms a barrier that is permeable to water but not to oxygen.
Cool temperatures also allow the seed to digest some of its food reserve, giving it energy. For these seeds, putting them in the refrigerator for a specific period of time allows them to gain sufficient oxygen and energy to germinate Colorado Seed Laboratory To find out whether or not your seed is viable, do a germination test.
Wrap seeds in a moist paper towel, wait days, and count how many seeds germinate. Illustration 1: Steps of seed germination. If you save your seed from the year before, think about this: the life of a seed can be cut in half by an increase of just 1 percent in seed moisture or by an increase in storage temperature of just a few degrees. A simple rule of thumb is that the sum of the storage temperature in degrees Fahrenheit and percent relative humidity should not be greater than The primary root, called the radicle, is the first thing to emerge from the seed.
The primary root anchors the plant to the ground and allows it to start absorbing water. After the root absorbs water, the shoot emerges from the seed.
In dicots, the shoot has three main parts: the cotyledons seed leaves , the section of shoot below the cotyledons hypocotyl , and the section of shoot above the cotyledons epicotyl. The way the shoot emerges from soil or growing media follows two main patterns. In some plants, the section of the shoot below the cotyledons elongates and forms a hook, pulling the cotyledons and the growing tip through the soil.
Once it reaches the surface, it straightens and pulls the cotyledons and shoot tip of the growing seedlings into the air. For example, beans germinate this way. This is called epigeous germination. In other plants, only the section above the cotyledons expands, leaving the cotyledons underground where they soon decompose. This is called hypogeous germination.
Peas, for example, germinate this way Raven, Ray, and Eichhorn In monocot seeds, the primary root is protected by a sheath coleorhiza , which pushes its way out of the seed first. Then the seedling leaves emerge covered in a protective sheath called a coleoptile Raven, Ray, and Eichhorn After the shoot emerges, the seedling grows slowly while the storage tissue of the seed diminishes. Soon, the plant develops a branched root system or taproot. Then, true leaves that look like the leaves of the mature plant appear.
These leaves, unlike cotyledons, photosynthesize light into energy, allowing the plant to grow and develop. We know that seeds need optimal amounts of water, oxygen, temperature, and light to germinate.
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