An Avocado stone needs to be started off in the dark. It can be grown in compost, but it is easier and more interesting to put it first (small end up) in a narrow glass with water reaching half way up: you will be able to watch the initial root and shoot growth. Foil around the glass will keep light out but won't exclude air.

Put the glass near a radiator or hot tank and keep the water topped up. If the stone gets slimy, rinse it under the tap and put it back in clean water. The stone should start to split within a month or two, and a root and shoot will appear from it.

When these are an inch long, the stone should go into a 6 inch pot of compost. Keep it out of strong light until it is 3 inches tall. In years to come it will grow several feet high if it gets enough sunshine and protection from draughts. A stick for support and, in due course, a bigger pot are likely to be needed. Regular watering (with liquid fertilizer added) is necessary.