The slang term “bumper crop” refers to an unusually large harvest. Although this term refers specifically to agricultural products, some people also use it more generally to talk about any unexpected windfall, as in “there's a bumper crop of students enrolling this year.” As a general rule, a bumper crop is viewed as a very positive thing.
The origins of this term have their roots in the 1700s, when people started to refer to extremely large swellings as “bumpers.” A bumper crop was a harvest which was so large that it swelled the baskets and containers used to ship things to market. The origins of “bumper” also explain why the swellings on automobiles are called “bumpers,” although how the leap from swelling to killing was made in 1908 when people started using “to bump off” as a euphemism for murder is a bit unclear.
Bumper crops can happen for a number of reasons. Most typically, especially favorable environmental conditions encourage crops to produce in large amounts. Temperate weather, lots of rain at the right time, and ample sunshine when plants are developing can all lead to bumper crops. Farmers can also help the process along with the use of fertilizers, compost, and other materials designed to enrich the soil, providing lots of nutrition for plants to feed on, or by planting in excess to guarantee a high yield.
Often, the first year of decent yields after several years of decline is referred to as a “bumper year,” even if the yield is not particularly large when compared to historical crop yields. As a general rule, bumper crops generate profit for farmers because farmers usually lock in contract prices for their crops long before their crops actually grow. If crop yields have been minimal in prior years, farmers may be able to secure a very high price for their crops, thus reaping a windfall when a bumper crop comes in, although conversely, prices may be lower in the following year due to the glut.
Some crops are actually notorious for generating a bumper crop. Zucchini, for example, will produce prodigiously with little encouragement, as some gardeners have learned to their chagrin. In small towns in the temperate climates where zucchini thrives, residents are often inundated with zucchini from the plants of their neighbors, and zucchini “drive-bys” to dispose of unwanted vegetables have been known to occur.