Seed Pod Bursting

The cheapest and most satisfying way to raise plants for a garden is from seeds. A seed is the basic biological unit for the reproduction of all flowering plants. In a seed male and female genes are combined to give rise to offspring that are genetically unique. This enables a plant to evolve and adapt to changes in the environment.

From a gardeners point of view this variation can be desirable in that completely new varieties can be produced  though in some cases it may not be, such as in many fruiting plants or roses where any variation would alter the unique characteristics of different varieties.

Seeds vary enormously in their germination requirements but all need moisture, an adequate temperature, air and in some cases light. Some will germinate freely when conditions are adequate while others have evolved barriers which need to be overcome for germination to occur. Such seeds are said to be dormant. Where the climate alternates between warm summers and cold winter dormancy prevents seeds from germinating as soon as they are ripe. Dormancy also staggers germination, reducing competition between seedlings.

For gardeners, causes of dormancy need to be taken into account when attempting to germinate seeds. Some seeds have coats which contain a waterproofing that in normal conditions would be gradually broken down by low temperatures and by bacteria and fungi in the soil. Physically abrading the seed coat with sandpaper or chipping with a knife allows moisture to reach the seed embryo. This is known as scarification. A vice can be used to crack large nuts. In some cases soaking seeds in warm water will extract the waterproofing, enabling germination.

Some seeds with fleshy coats such as magnolias and sorbus species may have a chemical inhibitor that would normally be removed as it  passes through an animals gut. These seeds need to have the flesh cleaned off the seeds before attempting germination.

Some seeds which come from climates where winters are cold may need to be subjected to a period of cold before germination can occur. This is known as stratification. This can be achieved by sowing the seeds in a damp medium such as sand and refridgerating them for anything from 3 weeks to several months depending on the species.

In parts of the world where bush fires occur such as Australia and South Africa the seeds of some plants may be stimulated to germinate by chemicals in smoke. Germination may also be facilitated by the action of fire in cracking the seed coat.

There is a huge variation in the lifespan of seeds. This is known as viability and is influenced by the conditions in which the seeds are kept.  Some seeds lose their viability very soon after they ripen, while others can retain their viability for years, decades or even in rare cases centuries. Storing seeds in cool, dark, dry conditions can preserve their viability. Exposure to high temperatures or humidity may reduce their viability or kill them.