horticulture, stratification is the process of pretreating seeds to simulate natural conditions that a seed must endure before germination. Many seed species have what is called an embryonic dormancyand generally speaking will not sprout until this dormancy is broken.
For seeds of
trees and shrubs from temperate climates, stratification involves soaking and chilling seeds prior to sowing. This simulates natural conditions where the seeds would remain through a winteron cold, wet ground. Seeds will usually germinate promptly and uniformly after stratification. Unstratified seeds may take up to two years to germinate, if they do so at all.
In the wild, seed dormancy is usually overcome by the seed spending time in the ground through a winter period and having their hard seed coat softened up 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, its growth and subsequent expansion eventually break through the softened seed coat in its search for sun and nutrients.
In its most basic form, when the cold stratification process is controlled, the pretreatment amounts to nothing more than subjecting the seeds to storage in a cool (ideally +1° to +3°C; not freezing) and moist environment for a period found to be sufficient for the species in question. This period of time may vary from one to three months.
To accomplish this you merely place the seeds in a sealed plastic bag with moistened
vermiculite(or sandor even a moistened paper towel) and refrigerate it. Use three times the amount of vermiculiteas seeds. It is important to only slightly dampen the vermiculite, as excessive moisture can cause the seeds to grow mouldy in the bag. As such, err on the side of drier rather than wetter. To give an idea, it should not be possible to squeeze any dripping water out of the vermiculite.
After undergoing the recommended period of cold stratification, the seeds are ready to be removed and sown in the nursery bed for germination.
Many sources recommend using
peata combination of peatand sand, or vermiculitewhen cold stratifying seeds. [cite web
last = Dan
first = Meyer
title = Growing Wisconsin Trees From Seed
accessdate = 2008-07-01
publisher=University of Wisconsin College of Agricultural and Life Sciences] [cite web
title=Germination of Tree Seed
publisher=University of Iowa Extension
accessdate= 2008-07-01 ] [cite web
publisher=University of Minnesota Monarch Lab
title=Growing Milkweed] . The medium must be sterile to prevent harm to the
seedby pathogensincluding fungi. [cite web
title=Dependency of Lingonberry Seed Germinating Ability on Seed Age and Storage Method
publisher=International Society for Horticultural Science]
Preparing a stratifying medium
Use of a fungicide to moisten your stratifying vermiculite will help prevent fungal diseases. This should be used as stipulated by the fungicide manufacturer. (Note: a convenient and safe fungicide is Chinosol. It is primarily a disinfectant, non-toxic, and can be used in solution from 0.1% for prevention, to 0.5% for treating an existing infection. It is often recommended for growing succulents from seed, which are generally prone to mold, so it should work well also for any other seed germination. It is not usually sold as a pesticide, but is available from vintner suppliers, as it is used for wine making in small quantities.)
Different seeds should be placed in different bags rather than putting them all into one bag, and large quantities are also best split into several small bags. That way any fungal outbreak will be restricted to only some seeds. If no fungicide is used, a close check should be kept on the seeds, removing any which show signs of mould or become soft and with a decaying smell.
If an outbreak of fungus occurs, remove the seeds and re-apply fungicide, then place them in a new bag with new slightly moistened
vermiculite. Always keep the bag sealed. The stratifying seeds should be checked on a regular basis for either fungus or germination. If any seeds germinate while in the refrigerator, they should be removed and sown.
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 15-20°C. 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.
Soaking the seeds in cold water for 6-12 hours immediately 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 in stratification.
The time taken to stratify seeds depends on species and conditions; in many cases two months is sufficient to break the seed dormancy. After undergoing the cool moist treatment the seeds are ready to plant and will usually sprout in a few days to weeks.
owing and seedlings
seedlings, whether grown in pots or beds, benefit from good air circulation which discourages fungus growth and promotes sturdy stems. Potting and germinating medium/soil is not critical as long as the soil is light as well as lightly firmed down but not heavily compacted. Sterilised potting soil will minimize problems with "Botrytis" or " Pythium" fungal disease. These problems are much more likely to occur if air circulation is poor.
Most seeds need only be planted at a depth equal to their own thickness in order to germinate. Seeds planted outdoors are best planted little deeper to avoid disturbance caused by heavy rainfall. The soil should be slightly damp but never soaking wet, nor allowed to dry out completely.
Wikimedia Foundation. 2010.
Look at other dictionaries:
Stratification — is the building up of layers, and can have several meanings *Social stratification, is the dividing of a society into levels based on wealth or power. *Stratification in archaeology is the formation of layers (strata) in which objects are found.… … Wikipedia
Seedbed — A seedbed or seedling bed is a specially prepared box used to grow plants in a controlled environment before transplanting them into a garden. A seedling bed is used to increase the number of seeds that germinate. Once the seedlings have matured… … Wikipedia
Europe, history of — Introduction history of European peoples and cultures from prehistoric times to the present. Europe is a more ambiguous term than most geographic expressions. Its etymology is doubtful, as is the physical extent of the area it designates.… … Universalium
Life Sciences — ▪ 2009 Introduction Zoology In 2008 several zoological studies provided new insights into how species life history traits (such as the timing of reproduction or the length of life of adult individuals) are derived in part as responses to… … Universalium
Southeast Indian — Any member of the aboriginal North American Indians who inhabited what is now the southeastern U.S. The Southeast was one of the more densely populated areas of native North America, having an aboriginal population conservatively estimated at 120 … Universalium
Seed — A seed Audio IPA|en us seed.ogg|/ˈsiːd/ (in some plants, referred to as a kernel) is a small embryonic plant enclosed in a covering called the seed coat, usually with some stored food. It is the product of the ripened ovule of gymnosperm and… … Wikipedia
Indian natural history — Natural history in India has a long heritage with a recorded history going back to the Vedas. This article explores the history and people involved in this endeavour, with natural history being restricted to the broad fields of paleontology,… … Wikipedia
Sundew — Taxobox name = Drosera image width = 250px image caption = Drosera tokaiensis regnum = Plantae divisio = Magnoliophyta classis = Magnoliopsida ordo = Caryophyllales familia = Droseraceae genus = Drosera genus authority = L. subdivision ranks =… … Wikipedia
List of Cumacea literature — Extensive literature list on Cumaceans. Contents: Top · 0–9 · A B C D E F G H I J K L M N O P Q R S T U V W X Y Z A … Wikipedia
Philip James DeVries — Infobox Scientist name = Philip J. DeVries |200px image width = 200px caption = Phil DeVries field = Biologist work institution = University of New Orleans awards = MacArthur Fellowship (1988) Geraldine R. Dodge Foundation Fellowship (1993)… … Wikipedia