Shelf life of Neem oil

I still have some Neem oil (the straight stuff, from Ahimsa) that I purchased in the spring of 2010. I suspect it is past its "use by" date, but I can't find any information on the shelf life, or any way to test to see if it is still potent. It has spent most of its life in a cold storage room, at around 55 degrees, but there were times in the summer when it wasn't so cold -- it got near 70 degrees for a couple of months in the heat of 2012 and 2013, but has been in a cooler at 35 degrees now since last August. So its 4 years old. Time to get a new gallon? Can you increase the concentration to offset a loss of potency, or am I not even thinking about it correctly?

Turkey Creek Orchard
Solon, Iowa (zone 5A)

The constituent profile of pure neem oil remains relatively stable as long as the oil remains solidified and out of direct sunlight. When subjected to repeated "thawing" to a liquefied state at temps above 60°F, neem oil will deposit a thick black viscous layer called stearin, at the bottom of the drums and containers. That's not necessarily a loss per se. Fatty acids are especially vital in the holistic context, and neem contains a wide array beyond stearin.

A bit more is known about azadiractin content. Cold pressing of the mature seed kernel of the neem tree results in an oil with an azadiractin content as high as 3000 to 3500 ppm. This group of constituents is what gives neem its striking impact on insect development. Studies indicate that long time storage at a temperature above 30°C (86°F) results in the reduction of azadirachtin content below 1800 ppm. Extrapolate from there.

The upshot? It's reasonable to store neem for a year or two, perhaps even three, if a bulk purchase saves money in the long run. Ideally that larger container gets "thawed" but once, at which time the oil is poured into batch size containers. (If you need a quart of neem oil each time you spray, that then is the batch size for your orchard). Liquefy each batch gradually by bringing it out of cool storage the day before it's needed, and if it's still gunky in the morning, stick the jug in a pot of warm water for an hour or two. Don't use very hot water as this will reduce the effectiveness of the oil.

Finally, Peter, as to increasing the concentration to account for age ... absolutely not. Any oil proves phytotoxic at higher concentrations than the recommended 0.5% for foliar application.

Lost Nation Orchard
Zone 4b in New Hampshire



Edited 1 time(s). Last edit at 03/05/2014 12:30AM by Michael Phillips.