Let's face it, even though we all like to imagine that we would have been lords and ladies (if not indeed kings and queens) in the Middle Ages, any of us with European ancestors are descended from peasants.
This means that our ancestors were out there raising food, a complicated and very hard and unpredictable enterprise. Even today, farmers will tell you that raising food is possible only due to a few inches of topsoil (where most of the nutrients are) and the fact that it rains.
Most food raised was grain, wheat, oats, barley, which could be stored for a year or more without refrigeration (assuming the rats didn't get it) and ground into flour for bread. Without modern hybrid seed and modern fertilizers, peasants just had to hope that the ratio of grain planted to grain harvested was better than 2:1. At a 2:1 ratio, they would have to save half the harvest to plant next year and hope that the other half, the half they were eating, lasted the year. (With modern farming, the ratio of harvest to seeds planted is dozens to one.)
Of course one could always eat, rather than plant, the saved grain. Then you'd starve next year instead of this year. Great choice! There were constant decisions to be made, with no assurance of the right answer. Plant too early, and the wet ground might cause the seeds to rot rather than sprout. Plant too late, and there may not be a long enough growing season. Harvest too early, and the grain won't be ripe. Harvest too late, and chances of destruction (hail storm, locusts, birds) increase.
In the eleventh and twelfth centuries, European peasants made some bold decisions. Especially they started using a heavier plow (called a carruca), which would dig deeper and was fitted with a mould-board, to turn over the soil as one plowed. The carruca was only possible with improved metallurgy, such as led at the same time to the spread of horseshoes. It replaced the old, light-weight plow, the aratum, which while cheaper and easier to make would only dig a little way into the earth.
The carruca allowed farmers to plow only once, turning over the soil as they went in long strips, rather than having to cross-plow to get the soil properly turned over. This allowed farmers to cultivate rich, damp soils that would have been too wet to use with the old aratum. The image above is of a field plowed using modern farming techniques, but you can see the deep furrows and ridges made by a heavy plow.
It was bold to switch to an expensive new-fangled kind of plow. Also bold was to switch from so-called two-field farming, where one planted grain in half of one's land each year and left the other half to lie fallow, to regenerate itself and grow grass and weeds to be plowed under as "green manure." But also in the eleventh and twelfth centuries peasants started using three-field rotation, one third of one's land to grow grain, one third to lie fallow, and one third planted in legumes like peas and beans, which can increase nitrogen in the soil. Such decisions, however risky they seemed at the time, increased peasants' food production, making possible the economic growth of the central Middle Ages.