One of the commonest forms of dormancy found in seeds of trees, shrubs and flowers from the temperate regions is a biochemical control of embryo development, which has to be overcome by chilling.
There are two parts to this process: the imbibition of the seed, and then its exposure to a period of cold. The simplest way to deal with the problem is to sow these seeds in the open ground, where they will receive natural chilling. In a mild winter, however, there will be insufficient cold to overcome the dormancy controls, and so germination will be delayed for twelve months following a further winter's cold.
Thus to be sure of germination an artificial treatment known as stratification is required to complete the chilling process.
To obtain a suitable medium for stratification, first sieve dry sphagnum moss peat through a ^ in riddle. Mix about 4 volumes of this peat with 1 volume of water to produce damp peat that just exudes water when squeezed lightly in the hand. Then mix 4 volumes of this damp peat to 1 volume of seeds to give the seeds plenty of moisture. If the mixture looks compact, add 1 volume of grit to improve aeration. Place the mixture in a polythene bag and tie a label on the outside. Leave for two or three days in the warm while the seeds take up water and swell. The seeds are now ready for chilling. Place the bag in the refrigerator under the freezer box, where the temperature will be lowest (but not freezing). Turn and shake the bag every week to prevent compaction and to maintain aeration around the seeds.
The time needed for the seeds to chill is extraordinarily different and may vary from three to four weeks to 16 to 18 weeks depending on the species.
Many seeds will not be bothered by an excess of chilling period as they simply sit and*wait for the right conditions for germination in the spring, but some begin to germinate regardless of temperature once the required chilling period is complete.
Some seeds with hard or impermeable seedcoats can be prepared for sowing by treating the seeds with hot water. This extracts sufficient "water-proofing" and allows the seed to take up water and swell.
Using a ratio of 3 volumes water to 1 volume seeds, place the seeds in a shallow dish and pour water that has just gone off the boil over them. Do not use more than this ratio of water otherwise the temperature will be too high for too long and this may cause damage to the embryo. Place the dish in a warm environment; leave for 24 hours. If the seeds do not swell, repeat the exercise.
1 Sieve 4 volumes sphagnum moss peat through a riddle.
4 Mix all the ingredients thoroughly. Add 1 volume grit if the mixture looks compact.
2 Add 1 volume water to the peat so it exudes water when squeezed lightly in the hand.
3 Measure out 1 volume seeds and add to damp peat mixture.
5 Place the mixture in a polythene bag. Label and leave in warm area for two to tlyee days to imbibe.
6 Move polythene bag to refrigerator to chill. Turn and shake occasionally to maintain aeration.
Was this article helpful?