Scarification and Stratification


 


Before going into the pros and cons of Stratification & Scarification it might be worth while discussing why this is necessary in the first place.


What is Stratification?

In nature, seeds require certain conditions in order to germinate, this is where stratification sometimes comes into play.

Seed stratification is a process whereby seed dormancy is broken to promote germination.


For example: The germination of some seed species is triggered by the seed/s spending a period of time in the ground throughout the winter so that its hard seed coat can be softened by frost and weathering.

This cold moist treatment encourages the seed's embryo to grow and eventually break though the softened seed coat, however the timing of these procedures is critical!

The task/s must be timed to ensure that the environment is favourable for both the emergence, and survival of the seedlings.  

In nature; this timing usually takes place in autumn to coincide with the forthcoming cold temperatures, and / or the microbe activity on the fallen seed.


To be successful, one will have to treat some seed types to a warm, then cold then warm again treatment, and others to a cold period followed by warm one.

Which raises the question: Where can I get the information for specific seed varieties.


In most cases the required information will be written on the seed packet, if not; one should check in reference books, and or go on-line'.


Failing that probably the simplest wayto find out is to determine when the plant/s shed their seeds.

For example: In nature, Spring flowering plants will shed their seeds in late spring / early summer meaning that the seeds lie on/in the soil in the relative warmth of the summer, then they are subjected to the cold winter weather.

In spring as the soil warms up the seeds germinate hence the suggested warm / cold / warm treatment.

Note: These Spring flowering plants are not to be confused with the type of plants that likewise shed their seeds in late spring but go on to germinate in Autumn, then they over-winter as semi-dormant seedlings.

This type of plant is normally classified as a 'biennial' and does not need stratification as such.


Then there are the 'summer flowering' varieties who shed their seed in autumn meaning these seeds will only be subjected to the cold winter weather then they germinate in Spring as the soil warms up hence the need to apply cold / warm treatment.

Other factors that may take place in the wild is that fallen seeds may be covered naturally with fallen leaves and / or dead plant top growth, this detritus will offer some protection, but more to the point it will prevent them from being found and eaten by foraging wildlife.


How to Stratify seeds:


When seeds are purchased they are in a 'dormant' state' or at least they should be!!

If they are not, and they are showing signs of germination, this suggests that the seeds have not been stored properly, and they should be returned to the supplier!

There is no point in trying to grow them on as it is quite likely that any 'embryo' growth will have dried out rendering the seed non-viable!

If they are your own saved seeds dispose of them.


Method

Basically spring and autumn produced seeds require the same treatment apart from the fact that spring produced seed will need a warm period prior to the cold treatment.

Similarly; the cold period can be induced indoors by means of a domestic refrigerator, or by being placed outdoors in a coldframe during the winter.


Sowing:

Seeds can be sown into containers containing a proprietory seed compost on its own or mixed with either Perlite or Vermiculite.

If light is needed in the germination process then vermiculite should be used on its own or as a topping to let the light through.


Propietory Compost
Compost and Perlite
Compost and Vermiculite
Vermiculite

Alternatively they can be chitted in a plastic bag.


Containers:

Quite often the number of seeds being sown will determine the size of container.

Then there is the consideration if they are going to be placed in a domestic refrigerator alongside foodstuffs.

Here are a few container examples;


Plant Pot
Trays
Recycled Food container
Plastic Bag

Note: Soaking the seeds in cold water for 12 hours prior to sowing the seeds can sometimes speed up germination.

 

Cold stratification:


Cold stratification is the length of exposure (vernalizing) the seeds are subjected to for germination to begin.

The vernalization period required varies between seed types.

As a rule of thumb most seed species, will require a temperature of 2°-4°C (36°-40°F) for 6-8 weeks*

* More precise temperatures and durations are usually written on the seed packet, failing that; check on-line!


Warm Stratification:


In the case of spring produced seeds; the warm period is one month at 15-20°C (59-68°F) prior to subjecting them to Cold stratification.

After cold stratification (in both the spring and autumn produced seeds) the warm stratification period requires temperatures of 15-20°C (59-68°F) up until germination takes place.


The 'Chitting Method'


There are two methods of carrying out this task,(the choice is optional) in other words; the choice is entirely up to you.

The basic difference between the two is that when the seeds are folded into the paper towel they tend to remain static, whereas the exposed seeds have the potential to move around when the bag is moved.


Folded Method:


Equipment Required
Place seed on paper towel
Seed on towel
Fold paper and cover seeds

Place wrapped seeds in plastic bag
Wrapped seeds in sealable bag
Wet Paper towel
Seal Plastic bag

Place sealed bag in refrigerator at a temperature of 2°-4°C (36°-40°F) for 6-8 weeks, or follow instructions on seed packet!

Name and Date bag

After the stratification period carefully prick out the seeds into suitable containers containing a proprietory seed compost and treat them as you would with sowings any other type of seed.


Unfolded method:


Equipment Required
Seeds on Paper towel
Seeds in sealable bag
Wet Paper towel

Place sealed bag in refrigerator at a temperature of 2°-4°C (36°-40°F) for 6-8 weeks, or follow instructions on seed packet!

Seal Bag
Name and Date bag
 

After the stratification period carefully prick out the seeds into suitable containers containing a proprietory seed compost and treat them as you would with sowings any other type of seed.


Alternative Method:


Seal tray in plastic food bag and place it in refrigerator at a temperature of 2°-4°C (36°-40°F) for 6-8 weeks, or follow instructions on seed packet!

After the stratification period carefully prick out the seeds into suitable containers containing a proprietory seed compost and treat them as you would with sowings any other type of seed.

Sow seed and cover with vermiculite

Outdoor Method


Place tray outdoors till spring then fetch them into the greenhouse and propagate them at 15-20°C (59-68°F) until they germinate.

Once germinated treat them as you would do any germinated seedlings.

Sow seed and cover tray

Scarification


Scarification is defined as the weakening, opening, or altering the coat of a seed to encourage germination.

There are basically three means of achieving this and they are; Mechanical, Thermal, and Chemical scarification


Overview:


The seeds of many plant species are often so hard it renders them impervious to water and air, thus preventing or delaying germination.

To alleviate this problem one must 'scar' the seed coat so as to allow the ingress of moisture and air.


The most common type of scarification is mechanical scarification.

This is when the seed coat is abraded with a metalfile,sandpaper or nicked with a knife to weaken or slightly open the seed coat.

Nicking with a knife

Chemical scarification involves the use of chemicals to promote germination.

This is done by soaking the seeds in an acid solution of either dilute sulfuric acid or household bleach for varying amounts of time.

This method is rarely carried out by the amateur gardener and the mention of it here is purely for information purposes


Thermal scarification can be achieved by briefly exposing seeds to hot water.


Regardless of the method used, scarified seeds do not store well and should be planted as soon as possible after treatment, lest they become unviable.

Hot Water treatment

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