In horticulture, stratification is a process of treating
seeds to simulate natural conditions that the seeds must experience before
germination
Germination is the process by which an organism grows from a seed or spore. The term is applied to the sprouting of a seedling from a seed of an angiosperm or gymnosperm, the growth of a sporeling from a spore, such as the spores of fungi, ...
can occur. Many seed species have an embryonic
dormancy
Dormancy is a period in an organism's Biological life cycle, life cycle when growth, development, and (in animals) physical activity are temporarily stopped. This minimizes metabolism, metabolic activity and therefore helps an organism to conserv ...
phase and generally will not sprout until this dormancy is broken.
The term stratification can be traced back to at least 1664 in
John Evelyn
John Evelyn (31 October 162027 February 1706) was an English writer, landowner, gardener, courtier and minor government official, who is now best known as a diary, diarist. He was a founding Fellow of the Royal Society.
John Evelyn's Diary, ...
's ''
'', where seeds were layered (stratified) between layers of moist soil and the strata were exposed to winter conditions. Thus, stratification became the process by which seeds were artificially exposed to conditions to encourage germination.
Cold stratification
Cold stratification is the process of subjecting seeds to both cold and moist conditions. Seeds of many trees, shrubs and perennials require these conditions before germination will ensue.
In the wild,
seed dormancy
Seed dormancy is an evolutionary adaptation that prevents seeds from germinating during unsuitable ecological conditions that would typically lead to a low probability of seedling survival. Dormant seeds do not germinate in a specified period of ...
is usually overcome by the seed spending time in the ground through a winter period and having its hard seed coat softened by frost and weathering action. By doing so the seed is undergoing a natural form of "cold stratification" or pretreatment. This cold moist period triggers the seed's
embryo
An embryo ( ) is the initial stage of development for a multicellular organism. In organisms that reproduce sexually, embryonic development is the part of the life cycle that begins just after fertilization of the female egg cell by the male sp ...
; its growth and subsequent expansion eventually break through the softened seed coat in its search for sun and nutrients.
Cold stratification simulates the natural process by subjecting seed to a cool (ideally ) moist environment for a period one to three months. Seeds are placed in a medium such as
vermiculite
Vermiculite is a hydrous phyllosilicate mineral which undergoes significant expansion when heated. Exfoliation occurs when the mineral is heated sufficiently; commercial furnaces can routinely produce this effect. Vermiculite forms by the weathe ...
,
peat
Peat is an accumulation of partially Decomposition, decayed vegetation or organic matter. It is unique to natural areas called peatlands, bogs, mires, Moorland, moors, or muskegs. ''Sphagnum'' moss, also called peat moss, is one of the most ...
, or sand and refrigerated in a plastic bag or sealed container.
Soaking the seeds in cold water for 6–12 hours before placing them in cold stratification can cut down on the amount of time needed for stratification, as the seed needs to absorb some moisture to enable the chemical changes that take place.
Use of a
fungicide
Fungicides are pesticides used to kill parasitic fungi or their spores. Fungi can cause serious damage in agriculture, resulting in losses of yield and quality. Fungicides are used both in agriculture and to fight fungal infections in animals, ...
to moisten the stratifying vermiculite will help prevent fungal diseases.
Chinosol (
8-quinolyl potassium sulfate) is one such fungicide used to inhibit ''Botrytis cinerea'' infections.
Warm and cold stratification
Any seeds that are indicated as needing a period of warm stratification followed by cold stratification should be subjected to the same measures, but the seeds should additionally be stratified in a warm area first, followed by the cold period in a refrigerator later. Warm stratification requires temperatures of . In many instances, warm stratification followed by cold stratification requirements can also be met by planting the seeds in summer in a mulched bed for expected germination the following spring. Some seeds may not germinate until the second spring.
See also
*
Scarification (botany) – process to improve germination by making seeds more permeable
*
Vernalization – induction of flowering using cold
References
{{DEFAULTSORT:Stratification (Botany)
Horticulture
Plant reproduction