RE: Cold Stratification
- Subject: RE: Cold Stratification
- From: M* D* G*
- Date: Fri, 3 Aug 2001 09:32:46 -0700
Propagation Mailing list could help also on this query.
http://www.hort.com/lists/
Per Seed germination Database
http://backyardgardener.com/tm.html look at number 14
SPECIAL TREATMENT
12. Hard Seeds-Chipping
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.
Some of our geranium seeds have already been treated in this way when you receive them.
13. Hard Seeds-Soaking
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.
14. 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 doesn't usually benefit them to be actually in water or at temperatures below freezing.
Light also seems to be beneficial after prechilling 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.
15. Double Dormancy
Some seeds have a combination of dormancies 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.
16. Outdoor treatment
The above mentioned methods (12-15) 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.
We would also recommend you consult No. 6 which contains further practical suggestions regarding the special treatment of seeds.
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