Artificially enhancing the cold tolerance of plants.

15 years ago

I found this on another forum, and thought it sounded really interesting:

"A friend of mine in the East Coast zone 4b have great success with Nikita's Gift. There is a trick to increase the hardiness of some of the persimmon hybrids when their young. Spray a solution of 10% low biuret Urea two weeks after leaf fall. This increases the hardiness of the sap due to the higher solute content absorb. The more solute the sap has, the lower is the freezing point and the lower damages are from ice crystals.

This technique can even be done to plums, peaches, apricots that have swollen buds ahead of time. Simply spray the 10% urea (low biuret) during budswell, it increases the frost hardiness of the buds and subsequent flowers. Do not spray during flower opening, only up to pink stage."

1) Has anyone heard of this technique?

2) Would it work?

3) What is "Low biuret" urea (I know what urea fertilizer is, but never heard the term "low biuret" before)?

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Comments (7)

gonebananas_gw
15 years ago
"Low biuret" urea

Biuret is a compound incidentally synthesized in the manufacture of urea. It is not a problem in most uses of urea, including as a soil fertilizer, but is toxic to many plants (especially citrus) when applied as foliar spray. It is said by citrus experts to be great at greening up citrus that needs nitrogen. I have looked high and low for it for use on citrus. It turns out pure urea is illegal to sell in this state to regular citizens as fertilizer (antiterrorism hysteria; it can be used in explosives but in the same way that sugar and cotton and glycerine and toluene can; it is not like ammonium nitrate, a true danger) and the mail-order fertilizer sources don't mention biuret. I also don't see it in garden stores in neighboring states.
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Scott F Smith
15 years ago
Hmm, never heard of that. See link below for some study confirming this helped on avocados and peaches. I wonder how long the protection lasts; maybe not so long?

Scott

Here is a link that might be useful: study
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joereal
15 years ago
biuret is a condensation product during the manufacture of urea. if urea manufacturing quality control is poor, there would be biuret in the urea. biuret is toxic to some plants, especially evergreens, causing leaf necrosis and deforming small branches, but probably not toxic during dormant periods. Low biuret urea are more expensive. There is also a food grade quality urea which are used as yeast nutrient during wine making, and that is one of the more expensive forms of urea.

I posted the original quoted thread as a response to another member over at the Citrus Forum www.citrus.forumup.org

I have read several scientific articles that are internationally refereed about the use of solutes, including urea, by increasing the hardiness of subtropical and tropical plants through foliar applications.

The effect could last anywhere from one to two weeks. When the cold temperature is followed by warming spell, the solutes would have metabolized, so you should reapply at least 24 hours before the next forecasted frost or freezing event.

At best, the method could add 6 F deg added protection. For leaves, no more than 2% urea, for dormant branches, stems, and unopened buds, no more than 10% urea. Low biuret of course.
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denninmi
Original Author
15 years ago
Thanks, it sounds like this technique has some promise IF one can find the product. That sounds like the tricky part.

If the problem with regular urea fertilizer is that the biuret contaminant causes leaf burn, would it be ok to use regular urea on dormant persimmons, then, after they have defoliated for the season? I'm pretty sure that product is still available in Michigan, but frankly, I haven't tried to buy any in quite a few years, so, in the post 9-11 world, who knows?
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olpea
15 years ago
A couple years ago I heard of a cold hardiness trick that I saved in my files. I've never tried it because I'm in a pretty warm zone, but with yesterday's temperature drop (went from 59F to 3F in 24 hours) I may wish I would have tried this.

Passed down from an old fruit grower:
In the late fall on a day of 35F or warmer, spray the tree with rubbing alcohol followed by a spray of food grade calcium chloride. The old timer claimed it would increase the winter hardiness exponentially. Claimed it could be done again in the spring, two weeks before bloom to increase frost tolerance of flowers.

Don't know if this really works. If it does, it probably lowers the freezing point of the sap, the same way urea does. Don't know what concentration calcium chloride the gent used.

Potassium Dextrose Lactose (KDL) is a product specially manufactured to improve frost tolerance of blooms. Supposed to offer about 3 days protection. After that, it is metabolized by the plant/tree. Supposed to increase frost tolerance by up to 5F. I used some this spring, and recommend the lower of the two rates on the label. Even at the lower rate, it tended to want to burn the flowers a little, after a couple of sprays.

On obtaining urea. You might try a local farmer's coop. Ours sells it by the 50# bag, or bulk. I've seen people use it as ice melt in a pinch (years ago) although I wouldn't recommend it. For fertilizer, it doesn't take much, it's 50% N. For an area of 100sqft., you'd only use about a 1/2 lb.
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Michael
15 years ago
Lucky me, I walk over to the elevator 2 blocks away and scoop a 1 gallon bucket full of urea out of the bulk bin for free. One of the benefits of good relationships and living in a small town on the plains of Kansas.
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Embothrium
15 years ago
You can optimize the salt content of cell sap merely by keeping your trees adequately fertilized.
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Artificially enhancing the cold tolerance of plants.

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gonebananas_gw

Scott F Smith

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Artificially enhancing the cold tolerance of plants.

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gonebananas_gw

Scott F Smith

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