To freeze or to chill?
My last post was about starting Chilli seeds. In it, I mentioned that before starting seeds, you should use a fridge to refrigerate them, for three days. This is something I recently started doing. It is something recommended by no less than the creator of the Carolina reaper in his seed starting guide. The idea behind placing the seeds in
the fridge is to trick them into thinking it’s winter. Some schools of thought even recommend placing the seeds in the deep freeze to achieve this reaction. I thought I would do some research on the subject. What is best; to cool or to freeze?
While it is likely that some seeds will germinate faster if placed in the deep freeze, particularly plants that grow naturally in cold weather climates. But does this apply to Chillies? They originated in the Amazon basin (in Peru and Bolivia), after all, and certainly don’t like the cold!
My understanding is that the Amazon basin is a part of the world that doesn’t get very cold. If that’s the case, why should I need to put my seeds in a deep freeze? I am sure the Amazon basin never gets to – 20 degrees Celsius as our deep freeze does?
The origin of Chillies
Peru and Bolivia
On looking into it, I discovered that temperatures rarely go below zero except in the mountainous areas. In Peru, for example, the winter temperatures seldom go below 10 degrees Celsius. The coldest area in Peru is Lake Titicaca, where temperatures can go to minus four degrees. This is followed by Cusco, where the lowest winter temperature is one-degree Celsius. Bolivia, another country where Chillies have their origin, can have freezing temperatures in certain areas in the Andes. These include La Paz
(the capital of Bolivia), where temperatures can go to minus four degrees, and Lake Titicaca near La Paz (- 5 degrees). Bolivia and Peru share Lake Titicaca as a border
Now the only species I know of that comes from the mountains is C pubescens. This species includes Chillies like Rocotos. Rocotos are known for their cold weather resistance. In fact they grow best at between eight and fifteen degrees Celsius. So maybe this is a species that could benefit from placing its seeds in a deep freeze before starting them. However, I am not sure about that. I am currently growing Rocotos and found they germinated well in normal UK winter conditions, without me having to freeze the seeds
Based on the above, I think it is safe to rule out deep freezing seeds for planting at this stage. Seeds can probably be saved for long periods by freezing them. Seed banks even use cryogenics to do this, but is there any benefit in helping germination? I doubt it. In fact, unless the seeds are very dry when placed in the deep freeze, there is the chance that you may kill them. Moisture needs to be below ten percent, otherwise the centre of the seeds will freeze and form ice. This would definitely be the end of the seeds
Why place seeds in the refrigerator at all?
Stratification
I still believe that a seed needs to sense that there is a change going on. By using a fridge to prepare for seed starting, the seed is tricked into believing it’s winter. The temperature in a refrigerator at about three degrees Celsius emulates winter temperatures in some of the colder parts of Peru and Bolivia. When the seed is allowed to come to room temperature, it will think that spring has arrived . The seed now thinks it is spring and bingo – it germinates
That’s the theory. It all seems to fit together. However, for me, it needs to be proved
in practice. I want to see it with my eyes before I consider it written in stone. I also want to prove or disprove my theory that a deep freeze is not necessary for preparing Chilli seeds for seed starting
So, a couple of days ago, I placed some seeds in my deep-freeze. While I have already discounted the benefit of freezing the seeds before starting them. I thought it might be interesting to see what happens when you do. I wrapped each variety in aluminium foil and placed them in a watertight container. I then put them into the deep freeze. I also placed the same varieties (prepared in the same way with the foil etc) into the fridge. I intend to keep the seeds in these environments for three days. In the case of the Chillies in the deep freeze, I will thaw them for twenty hours before I start soaking them in chamomile tea. In the case of the seeds from the refrigerator, I will allow them to come up to room temperature for an hour or so. Then, they too will be placed into weak tea to soak. After they will be planted into my eggshells.
It will be interesting to see what happens, but that is the subject of another post
Image credit
The original uploader was JoeCarrasco at English Wikipedia./ CC BY-SA 3.0 / via Wikimedia Commons.
