Home Gardener's Propagation (UK Only). David Squire

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      HELPING SEEDS TO GERMINATE

      Seeds often appear to germinate in the most inhospitable of places, perhaps in cracks between concrete paving slabs and on the tops of walls; seeds of native plants often show this tenacity and adaptability.

      Each seed contains an embryo plant, surrounded and protected by a seedcoat and with a source of stored food. Germination is triggered by the presence of moisture, air and warmth, and when these are present germination occurs. Most seeds also need darkness; a few require light.

      • Moisture: Essential to soften the coats of seeds to enable roots to develop and shoots to push their way upwards through the soil or to the compost’s surface. At the onset of germination, a seed absorbs large amounts of water that stimulates growth; roots develop first, then shoots.

      • Air: All life processes, including germination, need oxygen. To enable oxygen to be available, compost must be well drained to allow air to reach the seeds. There is a desired balance in compost and soil between retaining sufficient moisture and allowing the presence of air; this leads to the practical advice for ‘moisture-retentive but well-drained soil or compost’.

      • Warmth: A suitable temperature is vital to initiate and encourage chemical activity within seeds when moisture and air are present. Seeds vary widely in the optimum temperatures they require. After seeds are liberated from a parent plant, they usually undergo a resting or dormant period that, for many plants, coincides with cold weather, and chilling seeds of some plants will encourage germination (see ‘Stratifying seeds’, right).

      • Light: Its influence on germination is variable and many seeds are able to germinate in both light and darkness. However, rather than just leaving seeds on the surface of compost or soil, it is best to sow such seeds at a depth that enables good root development and keeps them moist. The compost or soil also gives the subsequent seedlings a secure base. However, there are some seeds that will only germinate when exposed to light.

      VIABILITY OF SEEDS

      The ability of a seed to germinate when given suitable conditions (see left) gradually diminishes, and the question many gardeners ask is ‘how long will seeds remain viable?’ This depends on several factors:

      • Storage: The best ways to store seeds are described below.

      • Type of plant: This varies widely; whereas seeds of willows retain viability for only a few days, and those of Cocos nucifera (Coconut Palm) only slightly longer, seeds of Nelumbo nucifera (Sacred Lotus) are claimed to be viable for more than 100 years.

      Usually, it is the viability of vegetable seeds that interests gardeners. Here are indications for a few popular vegetables:

      Storing seeds

      If you are storing seeds gathered from your garden, it is essential first to remove pieces of debris from them; if left, they tend to rot and encourage decay in the seeds. Always collect seeds as soon as they are ripe (see opposite page).

      Both home-gathered and bought seeds (that may have been left over from the previous year) can be stored in a dry, dark, airy place with a temperature of 1–5ºC (34–41ºF). For many gardeners, storing seeds in paper bags in sealed glass or polythene containers in a cool refrigerator is the best solution.

      Stratifying seeds

      This is a way to encourage seeds to germinate by softening seedcoats and allowing water to enter. It involves soaking the seeds, then chilling them for several weeks to simulate their natural period of dormancy. It is used mainly for large, hard-coated seeds of shrubs and trees, including those of Amelanchier, Cotoneaster, Euonymus and some viburnums. Traditionally, the seeds were put between layers of sharp sand and left outdoors during winter, hence the name ‘stratification’.

      F1 hybrids

      In recent decades, seed companies have offered an increasing number of vegetables and flowers as F1 hybrids. This means that they are a first filial generation, the result of a cross between two pure-bred parents. Their progeny are large, strong and uniform. However, seeds saved from them will not produce replicas of the parents.