First, is there a radiator beneath the window? If so, that won't be doing it any good at all, while its running. Second, do you draw the curtains in the evening, leaving the plant between them and the window, particularly during winter? That's a chilly place to be at night. Third, is it waterlogged? If you leave it sitting in an outer container with excess water still in it, not tipped away 30 minutes after watering, that might have happened. Do you water only when the surface of the compost is dry to the touch, but not shrunken from the sides of the pot, and water thoroughly when you do it?

Otherwise, has it run out of root room in its pot? If there's roots hanging out the bottom, give it a larger container - if you're not sure, turn it out of its pot and inspect the rootball to see if its potbound.

Thanks bamboo for your comprehensive and helpful answer.

If you think where avocado naturally grow, they need lots of warmth and humidity. As Bamboo said near a radiator or on a cold window sill at night is not ideal. You could add some gravel to the container that the pot is standing in and keep the gravel wet. The water will evaporate and supply humidity to the leaves.

Another thing you can do is mist the leaves daily with water. Don't use tap water as it contains chlorine. Use rain water or de-ionised water.

Hope this helps?

Myron

Thanks Myron, I'll try those tips;especially the spray one- I live in a very dry flat: just hope it's not too late!