How to Germinate Seeds Successfully

How to Germinate Seeds Successfully

A plant seed is created to grow and will perform that task admirably once given the opportunity. For successful germination seeds need a suitable growing medium, moderate moisture and warmth to sprout, and enough light and space to thrive.

Soaking pea seeds to aid germination

Seed Preparation. Seeds should be stored in dry, airtight container until ready to be used. Check them regularly and discard any that are out of date or have signs of mould or rot. Before sowing it often helps to soak seeds in advance. Soaking breaks down the seed’s defences put in place to survive the winter and radically increases the moisture content, an important requirement for germination. Leave the seeds resting in a small bowl of water for 24- 36 hours before you plan to sow them. The protective seed coating may be scraped beforehand with a sharp knife or sandpaper to assist the water penetration. Clearly the sanding technique is only suited to larger seeds like peas or brans, life is too short to spend an afternoon sanding lettuce seeds.

testing seed viability with a germination test

Seed Viability.  All seeds will deteriorate over time, depending on species and storage conditions, affecting their ability to germinate successfully. Tomatoes, peas and beans can last up to 10 years, brassicas about 5 years and alliums will rarely be usable after 2 years. Seed viability can be tested prior to sowing in order to prevent wasted time and effort. Place seeds between sheets of damp paper towelling, keeping them moist and warm at a temperature of 21C. If the seeds have not sprouted after two to three weeks replace them with a fresh batch.

Conditions for Sowing. Germinating seeds need a warm, moist environment to initiate sprouting.  Most seeds will require a temperature around 18- 20C, although lettuce prefers a lower temperature, around 15C, for germination. They can be sown in a propagator to maintain this environment but a pane of glass or a plastic bag over the seed tray may be sufficient. A soil thermometer can be used and ventilation adjusted to regulate the temperature. The soil should be kept moist but not soaked.

Fine seed compost

Seed Compost. Seeds should be sown in fine compost containing minimal nutrient content. Most soils and garden composts are too rich and heavy to promote germination.  John Innes is a specially formulated compost mix containing a light, loamy growing medium with added sand and fertilizers. It is possible, with some practice, to make your own seed and potting compost. This can be achieved with use of vermiculite, leaf mould, sharp sand or coir mixed into your sieved growing medium to the required balance and consistency.

Sowing Methods. Small seeds can be broadcasted by scattering them thinly over the surface of the compost. They may be mixed with a fine, dry sand before sowing to obtain an even distribution and provide an easily visual indication of where they have landed.  After scattering, sift a layer of compost or fine vermiculite over the seeds. Larger seeds can be sown individually, known as station- sowing. Gently press each seed into the surface of the compost to a depth of 2cm or into a hole made by a dibber. Sow one seed to each plug if using modules or 2cm apart in a tray.  Small seeds can be managed easily by sliding them along a fold of paper with a pencil and guided into their sowing position. Some gardeners insist on sowing long thin courgette and seeds on their side to prevent water collecting and causing rot,  other gardeners though, seem to disagree.

Modular seed trays

Sowing Indoors. Seeds sown indoors, on a windowsill or a greenhouse, will enjoy the benefit of a controlled environment suited to successful germination. The correct temperature can be maintained according to a plant’s individual needs and moisture levels easily monitored and adjusted accordingly. A propagator or heat bench can be used to provide a warm, humid environment allowing planting to be started early in the growing season. Indoor sowing provides protection from pests, weeds and adverse weather conditions which could delay germination or damage fragile seedlings.

Sowing Outdoors. Seeds sown outdoors are generally sown in long drills to aid identification when thinning or transplanting young seedlings. As with indoor sowing, cover small seeds with a light compost and plant larger seeds to a depth according to the guidelines on the seed packet. It is worth bearing in mind that if the seeds are not to be thinned or transplanted then the seed spacing will be the final growing position of the mature plant. Environmental conditions play a big part in sowing outdoors, wait for a suitable soil temperature before planting and avoid adverse weather while sowing. In dry weather remember to water the bed before sowing. If possible protect the seed beds with a cloche or fashion mini greenhouses from cut down water bottles.

Thinning carrot seedlings

Thinning. As the seedlings develop it may be necessary to thin them to prevent overcrowding. Many plants tolerate transplanting, particularly onions, leeks and salads, and will benefit from the extra space. Small carrots have distinctive foliage and are easy to thin, with the baby carrots making a delicious snack. Some seedlings like beetroot grow in a clump and can be thinned easily by snipping the unwanted plants with nail scissors, avoiding root disturbance.

Tools and Equipment

Sieve - a fine mesh sieve is ideal for removing any large stones and grading compost into a suitable tilth for sowing.

Dibber -
this useful garden tool makes a perfect shaped hole for dropping a seed into without disturbing the surrounding compost or seeds.

Thermometer - maintaining the correct soil temperature is important for seeds to sprout.

Modular Cell Tray - available in a range of sizes for repeated sowing of plug plants.

Root Trainers - these deep cell modules are designed for peas and beans, allowing them to develop strong healthy roots without being disturbed.

Trays - general purpose soil trays for broadcasting seeds and supporting modular cells.

Propagators - perfect for creating the optimum environment for successful germination, available heated or unheated.

Seed Tin - a dry, airtight container is required if you are saving seeds or have leftovers from the previous year.