Yes. Plants can photosynthesize on cloudy days because sunlight still reaches leaves through and around the clouds. Cloud cover reduces or changes the light available, but it does not usually turn daylight into complete darkness. How much photosynthesis continues depends on the plant and conditions.
Why cloudy daylight still counts
Clouds scatter and absorb part of the sunlight passing through the atmosphere. Some light still reaches the ground as diffuse skylight from many directions. Chlorophyll can capture usable wavelengths from that light, so a leaf can continue building carbohydrates even without a clear view of the Sun.
Does growth slow down?
Often, but not in exactly the same way for every plant. When light is the limiting factor, lower light can reduce the photosynthetic rate. Shade-tolerant plants can use weaker light more effectively than sun-loving plants, while an extremely hot or dry sunny day can also limit photosynthesis through water stress and closed stomata.
What the leaf is actually doing
A photosynthesizing leaf uses light energy, water and carbon dioxide to make energy-rich organic compounds, releasing oxygen. The chemistry does not require direct sunshine at all times; it requires adequate usable light and favorable other conditions.
How this affects houseplants
Do not compensate for a single cloudy day by watering more; evaporation and soil drying may actually slow. For persistent low light, move a suitable plant nearer a bright indirect-light window or consider a properly positioned full-spectrum grow light. Monitor the specific species instead of assuming all plants want the same amount of light.
Frequently asked questions
Can a plant photosynthesize during rain? Yes, if sufficient light reaches the leaves.
Does a plant photosynthesize in complete darkness? Not through the light-dependent reactions in the absence of an alternative usable light source; however, plants still respire at night.
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