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Neem oil is best being stored in dark and cool conditions with the screwcap tightened.
Neem Oil Shelf Life
Storing Ourons neem oil or any other quality neem oil in good conditions will preserve the potency for 2-3 years. Stored badly (eg, in sunlight/warmth) the neem oil may lose potency after 12-18 months and so become less effective.
When neem oil goes bad
Neem oil mixed with water will deteriorate over a short space of time. Pure neem oil, by comparison, can last for months if stored in a cold, dark place.
Once it is mixed with water, aim to use your solution as quickly as possible- preferably in the same day. If stored, it can last up to two weeks, but this depends on the type or quality of neem oil you are using. Always check the label on the bottle to ensure you are storing it correctly and are not using bad quality neem.
When neem oil is solid
If your neem oil is solidified, it is possible to return it to a liquid form. The best way to do this is to expose it to indirect heat. A good way to do this is to place it near, or on, a radiator. Make sure you watch the neem oil closely, and remove it from the source of indirect heat once it turns back into a liquid.