Seeds stratification. How to do it?

As you learn to garden or grow plants from seed, you may have come across the term ‘Stratify’ or ‘Stratification’.  If it is a new term to you it can seem puzzling.  So, in this guide will be an explanation what Stratification is, why some seeds require it, and several methods you can use to Cold Moist Stratify your seed.

WHAT IS STRATIFICATION?
Stratification is the process where a seed experiences a set of conditions that will break its natural dormancy.  Via evolution process various seeds of plants have evolved to not germinate unless certain conditions have been met. 
For example, if a seed just needed moisture and warm temperature to germinate, then this could happen in Autumn.  A seed germinating in Autumn will probably not survive a cold winter. This is because it won’t have time to develop sufficient root structure.  Evolution has taught seeds from many plants to not germinate until they have spent a certain amount of time in a cold/moist environment.  This is the most basic (and common) method of stratification.
Other species of plants require rather unique forms of stratification.  For instance, Witch Hazel and Jewelweed require two winters before they will germinate.  So, the seeds need to experience a cold period, followed by warm, and again followed by cold before they will germinate.  Other species of plants have evolved to germinate after forest fires.

GUIDE ON HOW TO COLD STRATIFY SEEDS
There are two main categories to cold stratify seeds.  The first is winter sowing, which is the easiest, but not the best.  The other being simulating winters via the refrigerator.

How to Winter Sow Seeds
Winter Sowing seeds is very easy.  You just plant the seeds as you normally would, but place them outside during winter.  You want to make sure they are somewhat protected from drying out or from curious squirrels.  But, it is very easy to do this.  Many people just save milk-jugs, yogurt containers, or any other plastic container with a lid.
You can use regular plastic garden flat with seed cells, for example.
Then, fill it with moist soil, plant all seeds….then cover with a plastic dome.
Poke holes along the sides and top of the plastic dome to allow for some rain/snow melt to enter the container.
Finally, secure the dome cover with a piece of duct tape on each side, and twine wrapped around the entire tray/dome.
Place it outside in a shady area, or where it would only get morning sun (if any).  This is to avoid accidental germination, should a warm day occur in January.

How to Cold Stratify Seeds in the Refrigerator
Cold Stratifying seeds in the refrigerator is an option for you as well.  You can even do this by placing pots (with your seeds planted) directly in a spare refrigerator, etc.  Just make sure they are uncovered or else you may get a white fuzzy fungus.  But the most common methods involve sand or a moist paper towel.

How to Stratify Seeds using a paper towel
It is very effective way.  For smaller seeds it is the best method of stratification using a refrigerator.
1. Lay a paper towel out flat
Fold the paper towel once along the length, and once along the width.  Now you should have a quarter of the original surface area.
2. Unfold the paper towel, so that the exposed surface area is now half of the original.
3. Lightly mist the paper towel with a spray bottle.  If you can pick up and squeeze the paper towel, very little to no water should drip out.  If this is not the case, keep squeezing it until little to no water drips out.
4. Place your seed on one half of the now-moist paper towel (that is already folded in half once).
5. Fold the paper towel along the crease you previously made, so that the seeds are sandwiched between two layers of the paper towel.
6. Place this into a small zip-lock bag, label and seal it.
7. Put the zip-lock bag into the refrigerator for the required amount of days.

How to Stratify Seeds using Sand or vermiculite
Using a simple zip-lock bag and moist sand or vermiculite, you can stratify your seeds in the refrigerator.  This method is effective on larger seeds like legumes.  On smaller seeds, it would be difficult to locate  the seed within the sand or vermiculite mixture.  For smaller seeds, the paper towel method is suggested.
In a bowl, add a handful of sand/vermiculite and water, mixing the two together.  Only add enough water to moisten the sand/vermiculite. If water drips when you pick up the hand and squeeze, then it is too wet.  Add some more sand and try again.
Then, mix your seed with the sand/vermiculite.  You want the seed to have good contact with the moist sand/vermiculite.
Place the sand/vermiculite and seed mixture into a ziplock bag, and label it with the type of seed and date.
Put the bag in the refrigerator for the required amount of time, then remove and plant the seed as you normally would.

That’s it!  There are many other variants out there that you could try for stratification as well.  But, these were just a few of the easiest methods often  used. Good luck!

Information source: Joe Foster, Growitbuildit.com