Seeds Germination Guide

A method which has proved useful for not only small delicate seeds but for a wide range of types is the Polythene bag method. The seeds should be sown on the surface of the moist compost, covered to their recommended depth if necessary and the container is then placed inside a Polythene bag after which the end is sealed with an elastic band. The bag should ‘fog-up’ with condensation within 24 hours and if this does not occur place the container almost up to its rim in moisture until the soil surface glistens, then replace in the bag and reseal. The bag is not removed and normally no more watering is required until the seeds germinate. However, it is wise, if left for a long period to check the compost occasionally.

The seed container, bag etc. should be placed in a well lit place with a steady temperature. As soon as a fair number of the seedlings emerge remove the polythene bag, lower the temperature a few degrees and provide plenty of light, but not bright sunshine, to ensure that sturdy seedlings develop. It is also helpful to spray the seedlings occasionally for the first 14 days.

Some seeds need a period of moisture and cold after harvest before they will germinate-usually this is necessary to either allow the embryo to mature or to break dormancy. This period can be artificially stimulated by placing the moistened seed in a refrigerator for a certain period of time (usually 3- 5 weeks at around 41 F). With tiny seeds it is best to sow them on moistened compost, seal the container in a Polythene bag and leave everything in the refrigerator for the recommended period. However, larger seeds can be mixed with 2-3 times their volume of damp peat, placed direct into a Polythene bag which is sealed and placed in the refrigerator. Look at seeds from time to time. The seeds must be moist whilst being pre-chilled, but it does not usually benefit them to be actually in water or at temperatures below freezing. Light also seems to be beneficial after pre-chilling and so pre-chilled seeds should have only the lightest covering of compost over them, if any is required, and the seed trays etc. should be in the light and not covered with brown paper etc.

This page is meant as a general guide only as all packets of seeds will be sent with their very own guide to give the best possible germination results.

Soaking is beneficial in two ways; it can soften a hard seed coat and also leach out any chemical inhibitors in the seed which may prevent germination. 24 hours in water which starts off hand hot is usually sufficient. If soaking for longer the water should be changed daily. Seeds of some species (e.g. Cytisus, Caragana, Clianthus) swell up when they are soaked. If some seeds of a batch do swell within 24 hours they should be planted immediately and the remainder pricked gently with a pin and returned to soak. As each seed swells it should be removed and sown before it has time to dry out.

The above mentioned methods accelerate the germination process and help to prevent seeds being lost due to external hazards (mice, disease, etc.) but outdoor sowing is just as effective albeit longer. The seeds are best sown in containers of free draining compost and placed in a cold frame or plunged up to their rim outdoors in a shaded part of the garden, preferably on the north side of the house avoiding cold drying winds and strong sun. Recent tests show that much of the beneficial effects of pre-chilling are lost if the seed is not exposed to light immediately afterwards. We therefore recommend sowing the seeds very close to the surface of the soil and covering the container with a sheet of glass. An alternative method especially with larger seeds, is to sow the seed in a well prepared ground, cover with a jam jar and press this down well into the soil so that the seeds are enclosed and safe from predators, drying out etc.

Some seeds have a combination of dormancy’s and each one has to be broken in turn and in the right sequence before germination can take place; for example, some Lilies, Tree paeonies, Taxus need a three month warm period (68-86’F) during which the root develops and then a three month chilling to break dormancy of the shoots, before the seedling actually emerges. Trillium needs a three month chill followed by three months of warmth and then a further three month chill before it will germinate.

Some seeds can only germinate in standing water. You sow the seeds as per the species and then place the pot or tray in to another container/tray that is constantly filled with water so that the surface of the compost is gleaming. Take care not to water from above. Once there is sufficient germination you remove the seed tray and treat as normal.

Some seeds, e.g. Sweet peas, lpomaea etc., have hard seed coats which prevent moisture being absorbed by the seed. All that is needed is for the outer surface to be scratched or abraided to allow water to pass through. This can be achieved by chipping the seed with a sharp knife at a part furthest away from the eye, by rubbing lightly with sandpaper or with very small seed pricking carefully once with a needle etc.