All about Seed Stratification

If there is one thing that makes ornamental plant seeds stubbornly refuse to germinate, it is the lack of a cold period. In nature, it is simple: a seed falls to the ground in autumn, spends winter in moisture and low temperatures, and wakes up in spring. This is natural stratification – and you can easily replicate it at home.

Depending on the plant species that REQUIRE stratification, the ideal time to start is from late autumn to the first half of winter. If you begin at the right time, by March or April you can already have seedlings.

Stratification in the Fridge? Easy!
You will need:
a transparent resealable (zip-lock) bag,
a paper towel,
vermiculite / peat,
a little moisture,
seeds (the most important part, of course).

How to do it:
1. Moisten the vermiculite so that it is damp but not soaking wet.
2. Put the vermiculite into the bag so that the ratio of vermiculite to seeds is about 5:1.
3. Add the seeds and mix or spread them evenly.
4. Gently squeeze out excess air and seal the bag.
5. Write the plant name and the date on the bag.
6. Place it in the regular (above-freezing) compartment of the refrigerator for 4–12 weeks. The exact period should be specified in the seed germination instructions.
7. IMPORTANT: once a week, briefly open the bag to ventilate it and check that there is no mould and that there is still enough moisture.
8. When the stratification period is over, sow the seeds into substrate.

Natural Stratification Outdoors
This method is especially appealing to those who want something “more natural” or “even simpler”. But REMEMBER: by choosing this method you give up a good part of your control over germination. In simple terms – nature will decide whether it wants new seedlings or not. Frequently changing weather conditions, rodents and other natural factors, unfortunately, can reduce germination significantly.

How it is done:
1. Fill a small pot or seed tray with soil. It is best to use clean soil, ideally freshly bought potting mix.
2. Scatter the seeds on the surface or press them lightly into the soil (how deep they should be sown depends on the germination instructions for that particular seed).
3. Water lightly and cover with a thin layer of horticultural fleece or similar protective cover.
4. Leave the pot or tray outside for the winter (there is no need to be afraid of snow).
In spring, simply keep an eye on it – once germination starts, move the seedlings into a greenhouse or another more controlled environment.

The Most Common Stratification Mistakes (and How to Avoid Them)
1. Substrate too wet – seeds rot or become mouldy.
2. Bag completely airtight with no ventilation – a minimum amount of ventilation is needed once every 1–2 weeks.
3. Stratification period too short – the seeds do not “wake up”.
4. Lack of moisture – cold and wind dry out the substrate and the seeds dry out and die.

Always read the germination instructions very carefully. The fewer failures you have, the better the final result will be.