How Does Shade Change the Temperature of Soil?

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How does shade change the temperature of soil? In the two sources used here, cover that shades the ground keeps the soil cooler during the warm part of the year, and it also reduces how far the soil temperature swings from day to night. Shade from a crop canopy and shade from trees and shrubs are described in different settings, so the answer below keeps the two studies separate. The aim is to explain what each one measured, how the effect reaches into the soil, and where the sources stop.

Quick answer

• Plant and tree cover that shades the ground lowers soil temperature, most clearly in summer.
• In a city-wide study, soils under trees and shrubs had lower summer temperatures than soils under herbaceous vegetation such as lawns.
• In an older field study with a dense oat cover, the soil at 10 and 20 cm was cooler than bare soil once the cover began to shade it.
• Shade also damps the daily swing in soil temperature, although neither source measures light directly.

What shade does at the soil surface

Shade acts at the ground surface first. The city-wide study describes trees in an urban area as mitigating elevated temperatures, particularly at the ground surface, by providing shade. The older field study describes the same kind of event in a crop: the cereal began to shade the soil surface about June 20th, and from that point the soil behaved differently from bare soil.

The effect does not stay at the surface. The city-wide study notes that both diurnal and seasonal surface temperature changes can be detected down into the soil profile to at least 20 to 30 cm. That depth is the reason the surface measurements matter for the roots below, even though the measurements themselves are taken at the top.

The city-wide study

The first source is a study from a mid-sized UK city. The authors buried temperature loggers at the surface of greenspace soils at 100 sites, and they compared sites by three factors: the type of vegetation, whether the land was a domestic garden or non-domestic greenspace, and the distance from the city centre. The data covered 11 months, so the comparison spans a full annual cycle rather than a single hot spell.

The vegetation groups were herbaceous cover, which in this study was mainly lawns, and trees and shrubs. The comparison was designed to ask whether woody cover changes the soil surface temperature, and by how much, compared with mown grass. That design is the main reason the study is useful for a question about shade: the two groups differ mainly in the amount of overhead cover.

What the city-wide study found in summer

The main result is in the summer months. The study reports that vegetation cover affects soil surface temperature, specifically that soils beneath trees and shrubs have lower summer temperatures than soils beneath herbaceous vegetation. In non-domestic greenspace, the average temperature beneath herbaceous vegetation was more than 3 °C higher than beneath trees and shrubs during the summer months.

The study also reports a larger effect on the daily maximum. Trees and shrubs in non-domestic greenspace reduced mean maximum daily soil surface temperatures in the summer by a clear margin compared with herbaceous vegetation. Those figures are the summer comparison, not an annual average.

Shade also changed the size of the swing. The study reports that the overall amplitude of mean residual temperature variation across the year was more than double in herbaceous vegetation than under woody vegetation. The study reads that as evidence of the effectiveness of trees and shrubs in buffering temperature extremes, especially in the summer.

Where the cooling was weaker

Not all woody cover did the same job. The study reports that trees in domestic gardens, which tend to be smaller, were less effective at reducing summer soil surface temperatures. Woody vegetation in domestic gardens only slightly reduced mean daily temperatures, and in March and April it tended to increase temperature extremes compared with lawns and other herbaceous vegetation.

The study also reports a winter pattern. Trees and shrubs in non-domestic greenspace tended to maintain slightly higher temperatures in winter. The study reports this winter result as a separate finding from the summer cooling.

Distance from the city centre

The city-wide study tested whether the urban heat island changes the picture. Proximity to the city centre increases soil surface temperature, especially in the summer. The study says the effects of the urban heat island are most apparent at night.

The study also notes that trees in an urban area may retain heat at night. The reason it gives is that trees may also retain heat at night by restricting movement of warm air. The passage presents this as a counterpoint to the cooling benefit of woody cover.

What the older oat field study measured

The second source is an older study from the Frost Research Station at Pelsonsuo. It compares soil with a plant cover against bare soil. The cover on the sites consisted of fully dense oats, and the soil temperatures were measured with thermocouples. Two thermocouples were used at depths of 10 and 20 cm at each point of measurement, and only one thermocouple was inserted 100 cm below the soil surface.

The main finding is that the cover changed the temperature once it began to shade the ground. The study says that after the plants have begun to shade the soil surface, the daily mean temperature at a depth of 10 and 20 cm has been lower than on the sites with bare soil surface. The cover also changed the daily pattern. The study states that the plant cover also damps the daily variation of temperature in the soil.

The depth pattern is also described. Under bare soil the temperature at 10 cm falls below that at 20 cm in the first half of September, whereas on the plant-covered sites the temperature at 10 cm has been higher than at 20 cm throughout the time of investigation. The study adds that the influence of the plant cover is also evident in the temperature at 100 cm depth. The cover therefore affected the soil well below the surface, not only the top few centimeters.

Why the two studies are not the same test

The city-wide study measured surface loggers across many greenspace sites, with a comparison between trees and shrubs and lawns. The oat study measured soil at fixed depths under a crop cover. The two studies point in the same direction: cover that shades the soil keeps it cooler in summer and damps the daily swing. But neither one isolates shade on its own.

That difference matters for a garden. A lawn, a shrub and a tree each cast a different pattern of shade, and the sources do not measure those patterns. The studies support the general direction of the effect, not a precise number for any one bed.

How we chose

The first source was chosen because it is a peer-reviewed article in the open-access PubMed Central archive that measures soil surface temperature at many sites over a full year. The second source was chosen because it measures soil temperature at fixed depths under a plant cover, which addresses the shade question directly. Each factual sentence in this explainer is tied to a passage in one of the two sources.

What we could not verify

The two sources do not give a measure of shade itself, such as the amount of light that reaches the ground, so this explainer does not state how much light blocks how much heat. The sources also do not measure soil moisture, so no moisture effect is claimed.

What the sources do not say

The urban study covers one UK city, and the oat study covers one site in a northern climate. Neither study gives a result for a sunny garden bed in a warm climate. The header of the older PDF is cut off at the year of publication, so the exact year is not confirmed here. The sources also do not give a recommended planting density or a recommended shade level for any crop.

Frequently asked questions

Does shade always make soil cooler?

The sources show cooler summer soil under trees and shrubs and under a dense oat cover, but neither one measures shade alone. The oat study describes the soil as cooler once the plants have begun to shade the surface, and the urban study reports lower summer temperatures beneath woody cover.

Does shade stop soil temperature from swinging?

Shade reduces the swing in the two sources. The oat study says the plant cover damps the daily variation of temperature in the soil, and the urban study reports that the amplitude of the annual variation was more than double under herbaceous vegetation than under woody vegetation.

Are small garden trees as effective as trees in a park?

The urban study reports that trees in domestic gardens, which tend to be smaller, were less effective at reducing summer soil surface temperatures than trees in non-domestic greenspace.

Why can soil under trees stay warmer at night?

The urban study says trees may also retain heat at night by restricting movement of warm air. The cooling from shade in the day can therefore be partly offset by slower cooling after dark.

How deep does the surface effect reach into the soil?

The urban study says that surface temperature changes can be detected down into the soil profile to at least 20 to 30 cm. The oat study measured effects at 10 cm, 20 cm and 100 cm depth.

For the same surface-cover idea applied to a different question, see why plants need mulch. For how a cover of snow changes the soil below it, see why snow insulates soil.

Sources

• PubMed Central, “Soil surface temperatures reveal moderation of the urban heat island effect by trees and shrubs,” https://pmc.ncbi.nlm.nih.gov:443/articles/PMC5027384/ (opened 2026-10-28)
• Pessi, Yrjö, “On the influence of plant cover upon soil temperature,” Frost Research Station, Pelsonsuo, https://journal.fi/afs/article/download/71437/33234/95520 (opened 2026-10-28)