In the context of developing nations or other pre-industrial cultures, most farmers practice a meager subsistence agriculture - a simple organic farming system with simple crop rotation or other techniques to maximize yield, using saved seed which is native to the ecoregion. In developed nations such a person using simple techniques on small patches of land might be called a gardener and be considered a hobbyist - or driven into such primitive methods by simple poverty.
In the context of developed nations, a farmer (as a profession) is most usually defined as someone with an ownership interest in crops or livestock, and who provides labour or management in their production. Those who provide only labour but not management, and do not have ownership, are most often called farmhands, or, if they supervise a leased strip of land growing only one crop, as sharecroppers or croppers. In the context of agribusiness, a farmer can be almost anyone - and can legally qualify under agricultural policy for various subsidies, incentives and tax reliefs.
Because of this diversity of terms, and the availability of money for those who 'qualify' as farmers, grower is a more neutral word for this lifeway.