Anytime! They will root easily. Then, put them in a pot with well drained soil, and keep them as a houseplant during winter, and put them outside during warm weather. They love sun, but do fine indoors in light areas. Just understand it will take many years for them to fruit, and then they will not be true to the variety you bought at the store. Seedling fruit is often bad, but you could get lucky! If you live in a climate with warm winters, it will thrive outdoors in ground as long as it is in well drained soil. Avos are thirsty. They like water.