Have you ever picked up a packet of seeds only to read the instructions which state to stratify the seeds before sowing? Occasionally it is not so simple as simply putting the seeds into compost for best results.
What Is Stratification?
Certain types of seed, most commonly from perennials, shrubs and trees require a period of dormancy in cold and moist conditions to stimulate germination.
This is built into the seed to prevent them from germinating too early or in the wrong conditions.
Buying a packet of seeds and sowing into potting compost may end up with very poor germination rates. To prevent this we need to stratify the seeds.
Stratifying or stratification is a term to describe simulating natural conditions in order to stimulate the seed to grow.
The two things that we want to do is keep the seeds:
- Moist
- Cold
This typically means keeping the seeds in moist and cold conditions for a period of time before you intend them to germinate.
This Happens Naturally
Seeds that germinate in the wild will spend a winter being worked into the soil in the weather.
This cold winter and the wet weather over this period is enough to weaken the hard out shell of the seed to the point where the seed can germinate when the weather warms up enough.
Do All Seeds Need To Be Stratified?
It is not necessary to stratify all seeds before they will germinate. In general, it is seeds of plants like perennials or shrubs and trees that will need stratification.
Most annuals will germinate without cold stratification and the seed packet will always state whether you need to do this so make sure you read the sowing instructions before you start planting.
Of course, if you don’t stratify seeds when it is recommended you should, some may still germinate but the rate of germination will be much poorer.
Stratify Seeds By Replicating Nature
We can easily accomplish the same thing that would happen in nature and create the conditions necessary in order to stratify seeds at home.
The main thing you will need is a place to store the seeds cold which is easy enough if you have a small amount of space in your fridge.
The other thing to consider is a way to keep the seeds moist. This along with the cold storage is the thing that will greatly improve germination rates.
How To Prepare Seeds For Cold Stratification
I find the easiest way to stratify seeds uses the following items:
- Sand or Paper Towels
- Ziplock Bag
- Bowl
To start with we need to moisten the sand, take a small handful of sand and place it in the bowl.
Add water a little at a time so the sand is just moist enough to form a clump when squeezed (like making sandcastles)
Empty the seed packet into the moist sand and give everything a thorough mix around to ensure the seeds are evenly distributed.
Pour the sand and seed mixture into a ziplock bag and seal. Label and date with the variety of seed and then place in the refrigerator.
Using Paper Towels
The same process as above can be accomplished with moist paper towels if you would prefer not to use a medium like sand.
Simply moisten paper towels and sprinkle the seeds on. Fold over to envelope the seeds and place this in a ziplock bag.
Label and date and place in the fridge.
How Long To Stratify Seeds?
Most seeds you buy will have detailed instructions on the packaging on how to stratify and prepare the seeds for germination but if they don’t, how long should you stratify seeds for?
The answer is anywhere up to three months which is what would happen in a natural setting.
You can shorten this time with a lot of variety of seeds to around 4 weeks and still get really good results.