In a hop garden, a fruit garden, a kitchen garden, both the rent of the landlord, and the profit of the farmer, are generally greater than in a corn or grass field. But to bring the ground into this condition requires more expense. Hence a greater rent becomes due to the landlord. It requires, too, a more attentive and skilful management. Hence a greater profit becomes due to the farmer. The crop too, at least in the hop and fruit garden, is more precarious. Its price, therefore, besides compensating all occasional losses, must afford something like the profit of insurance. The circumstances of gardeners, generally mean, and always moderate, may satisfy us that their great ingenuity is not commonly over-recompensed. Their delightful art is practised by so many rich people for amusement, that little advantage is to be made by those who practise it for profit; because the persons who should naturally be their best customers supply themselves with all their most precious productions.
-- Adam Smith, Wealth of Nations (1776), Bk I, Ch. XI, Pt. I, http://www.worldebooklibrary.com/eBooks/Renascence_Editions/wealth/wealth1.html