Dew is the name for the water droplets that sometimes appear on plants in the morning. This generally occurs in the spring or the fall, and is usually associated with cooler temperatures, which are more favorable for the formation of dew. It is the most common in coastal areas, and it often occurs in tropical areas too.

The best conditions for the formation of dew are a clear, cool night. Two separate layers of air must be present. The air closest to the ground must be high in humidity, and the air immediately above that is dry. Because there are no clouds to hold the heat in, as the night progresses, the ground slowly begins to lose the heat that it absorbed during the day. Eventually, the temperature of the ground is low enough to allow the moisture in the humid layer of air to condense. It condenses most easily on surfaces, which is why you see larger droplets on plants, tents, benches, and other similar surfaces.

The conditions that produce dew are very similar to those that produce fog, the only difference being the size of the moist air mass. Because of this, it is impossible to have fog without dew. It is still possible to have dew without fog, however. Because it is difficult to predict the depth of the humid air mass, it is often difficult to predict whether dew, fog, or both will occur.

Dew and frost are related, but not as closely as you might think.