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| To nick or not to nick, that is the question. |
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Ah yes, the question of nicking seed coats to aid germination. Simply put, scarification or nicking is an easy, quick way of allowing moisture into the seed to initiate germination by deeply scratching or removing a small section of the seed coat. I'm tossed on this question since there is no resounding blanketing answer of 'yes!' or 'no!’ This is why. Some seed, such as Gymnocladus, need scarification (aka nicking) in order for the seed to absorb water to trigger the proper metabolic process needed to wake the slumbering embryo and promote germination. This is because Gymnocladus evolved a reproductive strategy using very large seed dispersers, namely mastodon and giant ground sloth, to spread its species far and wide. By the time the animal was finished passing the seed through its gut, it was scarified, warm moist stratified (for days), and deposited at a new site. The processed ready to germinate seeds are physically bigger than its initial size as all swollen seeds are. Otherwise, Gymnocladus germination is near impossible; this is the reason why this species is classed as rare or endangered. So filing the seed coat, in this case, is a good thing.Sometimes nicking is not such a good thing. Some species, such as Paeonia and Cornus, have seed that develop hard coats and/or enter deep dormancy when not sown fresh. Others just develop a hard seed coat to withstand the elements during the moist stratification process protecting the embryo from invading pests and disease before spring arrives. These species include large ‘edible’ seed types like Ginkgo, Castanea, Juglans, Magnolia, Panax, Acer, and many others that need an extended period of cold (or warm) moist stratification. The moment the edible contents are exposed, it is rather like inviting all soil pathogens and nibbling creatures to an all-you-can-eat buffet. Many times nicking is used as a last ditch effort to jumpstart germination of old and/or improperly stored seed. As to define ‘improperly stored seed’, I suggest this for species that need specific storage requirements to maintain the viability of their seed and those needs have not been met. I continue shaking my head whenever I think about the stratified ginseng seed I ordered years ago. It came via courier service. The package sat on the heated dash, in the sun all day (though instructions on the label stated otherwise). The poor shriveled, abused, half-baked seed gave me extremely poor germination. None survived past two weeks. I could of put hours of work into nicking thousands of Panax seed to allow moisture in, but I only did about a hundred of the best looking candidates in the hopes of recovering something. Only a few weak seedlings managed to emerge from both nicked and unnicked seed but all succumbed despite my best efforts. The following year, using a different mode of transport and no nicking, germination exceeded 80%.Other plants have a strategy where the hard seed coat inhibits germination, allowing the seed to sit dormant for extended periods, until the conditions are right. The seed coat must be abraded, via soil grit, in order to allow moisture in. This is nature’s way, but in cultivation, my propagation book suggests nicking or scarification as the preferred re-sowing treatment for Canna, Baptisia, Hibuscus, Knightia, Isopogon and a few others. Most are tropical in origin. Tools can be simple as your thumbnail to gently scrape the outer coating to scalpels and files. Manual nicking allows a more controlled or uniform germination and more efficient use of time and resources for gardeners and nurserymen alike. Like a surgeon, you have to know where to cut so be warned, this process can seriously harm even mortally wound the embryo. If your knife, file or tool of choice goes too far and exposes too much of the white viable contents, you invite pest and disease. If you damage the seed ‘eye’ where the embryo is nestled, it’s as good as dead. So there you have it. People who specialize to a ‘few’ species have their own closely guarded secrets and scarification techniques. To date, Gymnocladus is the only species that I need to scarify. Germinating seed continues to be a learning experience and experience is the best teacher of all. I remember reading one propagation book that strongly suggested nicking peony seeds before sowing, so I dutifully nicked away processing about half my seed before stopping for the day. I sowed the treated and untreated seed side by side. The nicked seed ended up as some bug’s breakfast. The untreated seeds are now very nice plants. Lesson learned! So if you decide to nick treatment, use caution, use the proper tool, know where the ‘eye’ is, don’t nick all your seed and keep a germination log where you can write down your observations. It may sound silly now but when you read your notes days, weeks or years later, they will be invaluable. Again, experience is the best teacher of all. If there is one hard rule… never nick yourself!
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| For more information, please visit this article's web page. |
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| Published on Sunday 01 January, 2006. |
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