UNLOCKING THE MYSTERIES OF A SEED
In a seed lies the fierce force of life.. The drive within them is stronger than any other on our planet: that to survive. Growing a plant from a seed is one of the most satisfying feelings you can encounter in the garden. It’s like a miracle for me, to plant a seed in soil, then have flowers on the same plant a few months later, and to harvest more seed from it. If that seed came from a seed swap with Internet friends, it’s even more special! There is nothing better than free seeds from great plants. Much of this article comes from Growing Plants from Seeds by John Kelly.
SEEDS AND GERMINATION - What, exactly, is a seed? I don’t mean what does one look like, or where do they come from, or what do they do. I mean what IS a seed? If you really understand seeds and precisely what a seed is, your chances of getting good results with a wide range of seeds are greatly increased. Think of a seed as a combination lock. Sometimes it will wait a long time (maybe even a few years) to make absolutely sure that it has the right conditions to grow in. Generally, it will germinate if its four ‘locks’ are persuaded to open. What are these locks? Water, oxygen, light, and temperature. All four locks must be adequate before germination occurs.
To answer the question "What is a seed?" The reply could be that a seed is a liferaft launched by the parent plant in the hope that it will eventually find itself in a congenial place in which its embryo may develop, emerge and grow to maturity in order to produce yet more seeds. Before any seed can germinate it requires exposure to water, oxygen, the right level of light and the right temperature.
A seed will not be ‘unlocked’ with one watering. If it were, it would risk coming to life in an area much too dry for survival. It needs to ‘know’ that the water supply is adequate to support it, until it can send its roots down to deep layers where there is most likely more moisture. Germination begins when water penetrates the seed coat and initiates chemical changes within the tissues inside. Once begun, these changes can’t be reversed. If the water supply stops and the process is unable to continue, the seed dies. If you water your newly sown seeds and then let them dry out, you’ver probably killed a pot of healthy, eager seeds. They just about double in size in the process of taking up enough water to start germinating. The seed coat stretch slightly and then split, allowing more water and oxygen to come into contact with the contents and assist the growth.
Oxygen is vital to the chemical changes that go on inside as seed as it germinates. These involve the changing of food storage substances into sugars and proteins, and then into amino acids. These amino acids are used to build up tissues of the emerging plant. The process is called respiration, and it cannot take place without oxygen. A well-drained compost will go a long way to keeping a fresh oxygen-rich, airy atmosphere around the seeds. If it’s too sandy, it won’t hold enough moisture, and over-frequent watering will drive out the air for too much of the time; while watering too seldom will allow in plenty of air but not enough moisture. It’s obvious that providing the right conditions is a matter of balance.
Light is another ‘lock’ in a seed. A seed needs to know that it is near the surface of the soil and not too far down for its shoot to reach the sun and air. All seeds can tell is light and dark – a few inches might as well be a few feet. Darkness can have two effects – the seed will either die, or it can go dormant and could live for thousands of years. A few seeds need complete darkness to germinate, but they are very few. Look at seeds of plants that, in nature, live on the floor of a deciduous forest. They are often very small, and need to be sown on the surface so they have maximum light. This is because they ‘know’ that the leaves have not arrived above them and that it is a good time to make their early growth in the maximum light.
Every chemical process has a temperature range within which it can take place. If the temperature falls outside of that range, the reaction doesn’t happen. In plants, the range is narrow. If a seed is too cold or too hot, it will not germinate and some plants have very fine limits to the warmth they will tolerate, while others need much higher temperatures before they will germinate.
SEEDS AND DELAYED GERMINATION – Sometimes when you do all the right things to unlock all the keys, the seed still doesn’t germinate. There are a couple of reasons this could happen: the seed could be dead, or it could be dormant.
Seeds have different kind of different life spans. They will live longer in a cool, dry place than they will in a warm, damp place. Some seeds live only a few days, while others, like Poppies, can live for a thousand years.
Dormancy is another reason for failure. "Dormancy" is a generic term for all sorts of mechanisms that delay germination. Some seeds are dormant early in their lives to ensure they have time to get away from the parent plant. Others have a period of "after-ripening," which means that the seed is shed before it’s fully mature and maturity takes place over different intervals of time. Another kind of dormancy is demonstrated by seeds that will not germinate until they are ‘satisfied’ that certain seasons have passed. Some seeds have a coat that is so dry and hard that it takes a long time for it to break down and allow water to come in contact with the contents, or contain substances that inhibit germination until washed out by prolonged periods of moisture.
Something else to consider when we have failures is that some locks need to be ‘opened’ more than once, the locks may have to open in a specific order, or some locks may have to open simultaneously. Some plants are doubly dormant, like Peonies. They require a period of cool treatment followed by a warm spell. After that they will send out a young root from the seed. Only after further series of alternating temperatures will it send out a shoot.
Not to worry, there are ways of breaking dormancy and accelerating germination. Cold stratification, or giving alternating periods of chilling and warming will work quicker than a winter under snow. Treating the seed coat by chipping, filing, or soaking will help break through the hard seed coat. Providing bottom heat will ‘trick’ the seed into thinking it’s the right season to germinate.
Some seeds that need stratification include Iris, Aster, Rudbeckia, Aquilegia, Buddleia, Cleome, and Lavender. First, soak your seeds in water for 24 hours. Then, place them in a small amount of moist 50/50 vermiculite and peat. This is the mixture you will eventually sow the seeds in, so don’t use so much that the seeds will be deeply buried. Place this in a zip lock baggie and stick in the fridge. They will need 3 weeks to 3 months, depending on what kind of seeds you have. To get an idea of how long they need to be refrigerated, see THE SEED GERMINATION DATABASE. When germination begins, or when you feel it’s right to sow, fill some pots with a soil-less mix and sow the entire contents of the baggie on the surface.
Many members of the Legume family have very hard coats, Cannas are another example of seeds that will need to be nicked or chipped, and then soaked to allow water to reach the contents. Carefully nick seed sides with a sharp knife (don’t cut your fingers!), then soak in warm water for 48 hours before sowing.
Taking some of the mystery out of seeds will make growing your own plants from seeds much less intimidating. I’ve found a great seed germination database online that will tell you which seeds need to be stratified, scarified, or sown in place. Once you start one great plant from seed, you’ll catch the bug and want more. Check out my seed swap page when you feel you’re ready to make the plunge. I’ll be happy to supply the seeds!
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