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.
Stratification (cold treatment )
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.
The Bog Method
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
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.