What are they? Apples, pears, plums or something else. I would suggest that watering would be your biggest problem. I should say that I'm not a fan of fruit being grown in containers as this often puts them under stress. I would always look to grow fruit in the ground and some of the trees that are sold as mini varieties seldom give the rewards which you might expect. Sorry to be a kill joy! I'm sure that others will tell you of their successes with container-grown mini varieties.

I agree with Jimmy. A lot of companies sell these 'container fruit trees' as it's a good marketing ploy for them aimed at people living in flats with a balcony or a courtyard. A lot of these fruit trees aren't really suitable for growing in a container as the roots will be restricted, they need regular feeding and soil management.

Having said that, it depends on what type of fruit trees you are growing and what the circumstances are. For example, if it's a tender plant like citrus, then the only way that you could grow them over here would be in a container so that you could move them into a frost-free environment during the winter.

Even the smallest fruit trees need quite massive pots, around 70 cm wide and deep, and frequent, obsessive watering, to do well.