Dew

If you get up early enough, you may see tiny droplets of water glistening on lawns, leaves, flowers, and spiderwebs. Where does this water come from and how does it impact garden plants?

Dew on spiderweb (Rick Otten) Pexels

How does dew form?

Dew is usually formed at night when water molecules in the air come into contact with a cold surface, in a process called condensation. Evaporation is the opposite of condensation.

​You see it every summer when you have a cold drink. The glass is significantly colder than the surrounding air. Water molecules floating around in that air are attracted to and attach themselves to the cold cup. That’s how your iced tea glass gets so wet and that’s how plants get wet first thing in the morning. As temperatures drop below freezing, that dew becomes frost.

​What is dew point?

The temperature at which droplets will form is called the dew point. The dew point changes, depending on humidity and elevation levels.

​Pros and cons of dew

Dew is one way plants collect water. As the water droplets fall to the ground, plants are able to absorb the moisture through their roots. [There is even an organization dedicated to finding ways to harvest drinkable water from dew!]

Unfortunately, dew also provides habitat for fungal growths, such as potato blight (Phytopthora infestans), rust, and black spot. This is especially true for roses, which is why pruning for air circulation is such a good idea. In areas especially prone to dew, fans can be used to speed evaporation and reduce the likelihood of fungal growths.