Humidity

Quick definition

The amount of water vapor present in the air, usually expressed as a percentage known as relative humidity.

In plain terms

Humidity measures how much moisture the air contains.

When humidity is high, water evaporates more slowly from soil and plant surfaces. Leaves stay wet longer, which can encourage fungal diseases. When humidity is low, water evaporates quickly, causing soil to dry faster and increasing plant water demand.

Humidity varies by climate, season, weather conditions, and even location within a garden. Areas near walls, dense plantings, or water features may have higher humidity than surrounding spaces.

Why this matters

Humidity influences plant health, watering needs, and disease pressure. Understanding humidity helps gardeners adjust irrigation practices, improve air circulation, and reduce the risk of moisture-related diseases.

In practice

Examples

Humid summer weather often increases fungal disease problems.
Dry climates experience faster soil moisture loss through evaporation.
Greenhouses may develop excessive humidity without proper ventilation.
Dense plantings can trap moisture and create humid microclimates.

Practical applications

Improve air circulation through proper spacing and pruning.
Water at the soil level to keep foliage as dry as possible.
Monitor plants closely during periods of high humidity.
Use mulch to reduce moisture loss in dry conditions.
Increase ventilation in enclosed growing spaces when humidity becomes excessive.

Connected terms

Learn these first

Evaporation Transpiration Watering