Pea gravel consists of small, rounded stones, often available in colors like beige, tan, and white, making it a popular choice for pathways and decorative landscaping. While these light-colored materials are used to create a cooler surface compared to dark pavement, they still absorb solar energy when exposed to direct sunlight. How hot pea gravel gets depends on its material properties and the mechanics of solar heat transfer, which dictate how much energy is converted into surface temperature.
The Physics of Solar Heat Absorption
The degree to which any surface material heats up is governed by two physical properties: its reflectivity and its capacity to store heat. The first factor, known as albedo, measures how much solar radiation a surface reflects rather than absorbs. Light-colored materials like white or tan gravel have a high albedo, meaning they can reflect over 60% of incoming sunlight, which significantly limits the energy available for conversion into heat.
The second factor is specific heat capacity, which describes the energy required to raise the temperature of a material by a single degree. Materials like common rock, the basis of pea gravel, have a relatively low specific heat capacity. This means a certain amount of energy will cause a larger temperature increase in the rock compared to a material like water, which requires significantly more energy to warm up.
Temperature Profile of Pea Gravel
Pea gravel does get hot in the sun, with surface temperatures potentially exceeding 170°F. However, its unique composition prevents it from retaining heat as effectively as solid materials. The small, separated stones and numerous air pockets mean the entire layer has a low thermal mass, limiting its ability to store heat energy.
The low thermal mass allows the gravel to heat up quickly under intense sun, but the heat is not stored deeply within the material. Once the sun goes down or the gravel is shaded, this heat is rapidly released back into the surrounding air. Unlike dense concrete slabs, which continue to radiate heat long after sunset, pea gravel cools down much faster.
Environmental Factors That Increase Heat
Several external variables influence the final surface temperature of a pea gravel application. The presence of moisture is a significant modifier because water has a high specific heat capacity, meaning wet gravel requires more energy to heat up than dry gravel. Additionally, water evaporating from the surface draws thermal energy away, creating a cooling effect.
The surrounding landscape also plays a role, as heat can be transferred to the gravel from adjacent surfaces. Proximity to dark, heat-retaining structures, such as asphalt driveways or brick walls, can raise the temperature of the nearby gravel through radiant and convective heat transfer. A very thin layer of pea gravel will cool faster than a deeper layer because less material mass is available to absorb and retain solar energy.
Comparing Pea Gravel to Other Landscaping Materials
Pea gravel’s thermal performance is balanced compared to other common ground coverings, being both hotter than some and cooler than others. Pea gravel’s surface can reach temperatures significantly higher than green turf, which benefits from the cooling effects of evapotranspiration and moisture. Green grass in full sun may register around 114°F, while pea gravel can climb to 172°F under the same conditions.
Pea gravel performs better than many dense, dark hardscape options regarding heat retention. While dark concrete may reach a comparable peak temperature of 173°F, its high density and thermal mass allow it to store and release heat over a much longer period. Organic materials like wood mulch tend to remain cooler on the surface, reaching temperatures around 147°F, because they act as an insulating layer.