Sowing seeds that need cold temperatures to germinate
How to cold-stratify seeds
Many plants native to Central Europe need a period of low temperatures to trigger germination. In nature this makes perfect sense, ensuring that the seeds only start to germinate once winter is over. Normally these plants are sown outdoors in autumn, directly into the ground or in pots (the pots can be placed somewhere the plants are safe from predators).
Alternatively you can also sow these plants in a preserve jar and then place the jar in your fridge.
The seeds can germinate in the preserve jar and then keep growing there until the seedlings are large enough for pricking out. With their glass lids, preserve jars effectively function as mini-greenhouses – the rubber ring makes them watertight, ensuring that no moisture escapes, which means there’s no need to water the seeds in the early growth phase.
Coir compost works especially well as a substrate, but ordinary sowing compost is fine, too.
The glass makes it easy to check your seeds’ progress as they germinate.
This procedure works for most seeds that need cold to germinate:
- 2-4 weeks at a temperature around 20°C
- then around 2 months at below 5°C
- sometimes germination will start to happen in the refrigerator
- otherwise move the jar to a warm place after the cold phase
- if germination doesn’t happen put the jar back in the fridge
This method is a very flexible one.
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