Most seed is dormant and benefits from being pre-treated to ensure sufficient and even germination. Different species have different dormancy breakage requirements. Recommendations to break the different level of dormancy are given below but these should be used for guidance only as there is variation in depth of dormancy between different seedlots of the same species.
Non dormant e.g. oak, horse chestnut, sweet chestnut
These seeds are either not dormant at harvest or have a dormancy which disappears naturally during storage or in the soil when sown. They do not require any stratification.
Pre-chilled e.g. alder, birch, many spruces
These seeds are not actually dormant but will germinate faster and more uniformly if given a moist chilling (or pre-chill) at 0-2° C for up to 10 weeks. Soak seed in running water for up to 48 hours, drain thoroughly, place in a polythene bag, tie lightly and mix regularly during storage. The seed can be sown any time after three weeks of treatment.
Semi-dormant e.g. many firs, cedars
These seeds will not germinate completely unless they are given a moist chilling treatment. Use the same technique as that given under Pre-chill.
Mildly dormant e.g. rowan, sycamore
These seeds will not germinate at all unless given a lengthy period of chilling. The medium required is a mix of equal volumes of sieved peat with sharp sand. Mix fresh seed immediately with equal volumes of medium. Soak dry seed in running water for up to 48 hours, drain thoroughly and mix with equal volumes of medium. Dry seed often has more uniform germination if it is kept for 2 weeks at 18-20° C.
Place the seed and medium in a polythene bag and tie lightly. Store at 0-2° C. The number of weeks chilling required varies depending on the Species, e.g. rowan = 16 weeks, sycamore = 12 weeks. Mix the seed and medium twice weekly to allow fresh air to enter the bags.
Deeply dormant e.g. cherry, holly
These seeds are deeply dormant and require a lengthy period under warm and cold conditions before they will germinate.
Natural fluctuations in temperature are most effective, but the conditions can be given artificially using a warm room and refrigerator. The medium required is a mix of equal volumes of sieved peat with sharp sand.
Mix fresh seed immediately with equal volumes of medium. Soak dry seed in running water for up to 48 hours, drain thoroughly and mix with equal volumes of medium. Dry seed often has more uniform germination if it is kept for 2 weeks at 18-20° C.
The number of weeks treatment required depends on the species. e.g. cherry = 29 weeks, holly = 64 weeks. Mix the seed and medium twice weekly to allow the seed to breath.
Leguminous e.g. lupin, broom
These seeds are typical of legumes. A high proportion of the seed exhibit a condition known as hard seededness where a fine layer of wax prevents seeds from imbibing moisture. The wax must be punctured, e.g. by rubbing with sand-paper or by repeated soaking of unswollen seeds in near boiling water. Monitor the effect of treatment by soaking a sample in water - non-hard seed will swell, hard seed will show no signs of swelling. Continue treatment until at least 75% of seeds imbibe water easily.