Cold-stratification is a process that happens naturally in temperate climate zones: seeds that have fallen to the ground in autumn lie dormant through the winter, and only begin to sprout in spring when the weather gets warmer. In the seeds of many species there is actually quite a lot going on at a molecular level during the winter - chemical processes that are necessary for spring germination, meaning that if the seeds are not first exposed to winter temperatures, they wont germinate at all when it gets warmer.
Perennial vegetable seeds often need cold-stratification before they will germinate because many are relatively undomesticated species which retain their wild habits, whereas the common vegetables we grow as annuals have been bred to germinate quickly and reliably soon after they are sown in spring.
We can see this clearly with the Alliums. Most of the various cultivated varieties such as onions, leeks, spring onions, chives, etc. will sprout within a couple of weeks of sowing without any prior preparation. The wild Alliums, however, are another story.
Some other plant species that need cold-stratification, skullcap for example, need only a week or so. Others, such as vervain, good King Henry and valerian, will still germinate, albeit erratically, even without a period of cold.
The wild Alliums, however, generally need serious effort to get them to germinate outside their natural environment and among the most stubborn of them is Allium cernuum, or 'nodding onion'.
It is usually advised to sow Alliums and leave in a warm environment for a couple of weeks, then move to cold temeratures, where they will need up to eight weeks, before moving back to warmth, where germination will begin. This is good advice (though the initial period of warmth is not always necessary) however, it needs to be kept in mind that germination can take a long time after warming and if the stratification steps have been followed properly, it often pays to wait, even if it's starting to seem like the seeds have all died.
I sowed a packet of Allium cernuum seeds towards the end of January and left them outside. The pot has been sitting in the same place since then and over the last few weeks I've been looking at it thinking, 'if it hasn't happened now, it's never going to happen' while another little voice was saying, ', be patient, they've had a couple of months cold-stratification so they should sprout'. Well, four or five days ago I happened to check the pot in passing and the seeds had indeed started to sprout.
Perennial vegetable seeds often need cold-stratification before they will germinate because many are relatively undomesticated species which retain their wild habits, whereas the common vegetables we grow as annuals have been bred to germinate quickly and reliably soon after they are sown in spring.
We can see this clearly with the Alliums. Most of the various cultivated varieties such as onions, leeks, spring onions, chives, etc. will sprout within a couple of weeks of sowing without any prior preparation. The wild Alliums, however, are another story.
Some other plant species that need cold-stratification, skullcap for example, need only a week or so. Others, such as vervain, good King Henry and valerian, will still germinate, albeit erratically, even without a period of cold.
The wild Alliums, however, generally need serious effort to get them to germinate outside their natural environment and among the most stubborn of them is Allium cernuum, or 'nodding onion'.
It is usually advised to sow Alliums and leave in a warm environment for a couple of weeks, then move to cold temeratures, where they will need up to eight weeks, before moving back to warmth, where germination will begin. This is good advice (though the initial period of warmth is not always necessary) however, it needs to be kept in mind that germination can take a long time after warming and if the stratification steps have been followed properly, it often pays to wait, even if it's starting to seem like the seeds have all died.
I sowed a packet of Allium cernuum seeds towards the end of January and left them outside. The pot has been sitting in the same place since then and over the last few weeks I've been looking at it thinking, 'if it hasn't happened now, it's never going to happen' while another little voice was saying, ', be patient, they've had a couple of months cold-stratification so they should sprout'. Well, four or five days ago I happened to check the pot in passing and the seeds had indeed started to sprout.
And here they are again in a photo taken yesterday - they are growing fast.
So, if you've stratified your seeds your seeds properly and are wondering why they still haven't germinated and that maybe you got a packet of dud seeds... be patient and wait just a little longer, before throwing that tray onto the compost heap.
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