After sowing seeds, dividing plants and taking cuttings, care and attention is needed until the new plant is established and growing strongly. Advice on aftercare is given for each method of increasing plants.
SEEDS
Increasing plants from seeds
Are there many types?
There is a wide range of seeds, from dust-like to winged and plumed, and some are fleshy or hard (see below for details and their special needs when sowing). Sowing seeds is the main method of increasing plants, and usually the least expensive. It is often the key to capturing the attention of young children and turning them into gardeners. They are likely then to grow up into people who appreciate plants and respect the environment.
HARVESTING SEEDS
Although most gardeners buy fresh seeds of vegetables, hardy annuals, half-hardy annuals and greenhouse plants each year, some people like to harvest and save seeds from plants that have flowered. However, the plants that result from such seeds can sometimes be variable (gathering seeds is described below). In addition, where a plant is a hybrid – this is indicated by an x between the first (generic) and second (specific) names – its seeds will not breed true to the type; neither will those of varieties that are F1 hybrids (see box on opposite page for the meaning of this term).
TYPES OF SEED
Seeds can be grouped into six main types, and this has an influence on the way they should be sown.
• Dust-like: These very fine seeds soon lose their ability to germinate, and therefore are best sown while fresh. They include seeds of Begonia and Meconopsis. You need only press them into the surface of the compost.
• Hard-coated: Lathyrus odoratus (Sweet Pea) is an example; crimson and purple-coloured varieties have especially hard-coated seeds. To encourage rapid germination, chip the hard coat with a sharp knife on the side of the seed opposite the ‘eye’ (a process called ‘scarification’).
• Fleshy seeds: Seeds of some vegetables, such as beans and garden peas, have fleshy seeds; encourage germination by soaking them in water for a day or two before sowing. Aesculus hippocastanum (Horse Chestnut), Castanea sativa (Sweet Chestnut) and Quercus (Oaks) have fleshy seeds.
• Oily seeds: These include Magnolia seeds, and they soon lose their ability to germinate; you should sow them immediately after gathering.
• Winged seeds: Trees such as Acer pseudoplatanus (Sycamore), Fraxinus (Ash) and Tilia (Lime) have winged seeds; you can remove the ‘wings’ when you are cleaning them, and sow the seeds in the normal way.
• Plumed seeds: These include Erigeron and Scabiosa (Scabious); sometimes, if the plume is still present, they can be difficult to sow at the desired depth.
GATHERING SEEDS
When harvesting seeds, it is essential to choose a dry, sunny day and to keep the seeds of different species separate. The ‘parent’ plants should be healthy, free from pests and diseases and representative of their kind. Always gather the seedheads or pods before they begin to open. It is better for seedheads and pods to dry out slowly in gentle warmth, rather than quickly in a high temperature.
1 If the whole plant is nearing maturity, you can pull it up, invert it, place it in a thin paper bag and hang it in a dry, airy shed (see left). Alternatively, spread individual seed-heads and pods on sheets of paper and place them near a window so that they can ripen in full sun.
2 Once the seedheads are dry, clean the seeds by placing them in a sieve and gently rubbing or tapping (see left). When dry, place them in paper bags or other containers; then label and store them (see opposite page).
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:
| VEGETABLE | VIABILITY |
| Asparagus | 3 years |
| Beans | 3 years |
| Beetroot | 4 years |
| Broccoli | 5 years |
| Cabbages | 5 years |
| Carrots | 3 years |
| Cauliflowers | 5 years |
| Cucumbers | 5 years |
| Lettuce | 5 years |
| Onions | 1 year |
| Peas | 3 years |
| Peppers | 2 years |
| Pumpkins | 4 years |
| Radishes | 5 years |
| Spinach | 5 years |
| Squashes | 4 years |
| Sweetcorn | 2 years |
| Tomatoes | 4
|