Experimenting with Shade: Melons and tomatoes growing at UC Merced

July 30, 2026

UC Merced Shade Experiment At-A-Glance

• Size: 1 acre field with 3 plots – full sun, partial shade, full shade
• Shading: Wooden shade structures to mimic fixed-tilt solar panels
• Crops: Melons and tomatoes
• Irrigation: Sprinkler – even application of water in each plot
• Open for public visits: No, but stay tuned for info on new site in development

Researchers at University of California, Merced have made some interesting observations about the impacts of shade on melons and tomatoes. Conducted between May and September of 2025, a study led by Dr. Sarah Kurtz and PhD students Andrew Silverstein and Hossein Ashrafpour was designed to understand how fruit development would vary in fully shaded, partially shaded, and full sun plots.

Site Design

In a one acre field located at UC Merced’s Experimental Smart Farm in California’s semi-arid San Joaquin Valley, the team planted watermelon and tomato. Three plots were established: fully shaded, partial shade, and full-sun control. The fully shaded plot contained the plants growing directly under wooden shade structures to mimic a fixed-panel solar system. The partially shaded plot contained melons and tomatoes growing near the structures, with more light reaching the crops throughout the morning and less during the afternoon. The control plot was unshaded, with the crops receiving full sunlight throughout the day.

Many metrics were collected in order to determine what key variables were the most important to fruit development. Crop yield was the primary metric, and fruit quality as well as impact on harvest timing were also tracked during the growing season. Additionally, soil moisture and temperature were measured throughout the experiment in each region to identify variations across the shading regimes.

Key Results

CROP YIELD: The melons grown in partial shade were larger than those grown in full sun – 130% the weight. Melons grown in full shade, however, were smaller than those grown in full sun – 80% of the weight.

Tomatoes exhibited a different pattern, having 120% of the weight in full shade and 105% in partial shade compared to the full-sun control. This weight was not just a result of increased water in the fruit, as after dehydrating the produce, the shaded crop remained heavier than that grown in full sun.

Weight of Fruit

	Full Sun Control	Partial Shade	Full Shade
Melons	100%	130%	80%
Tomatoes	100%	105%	120%

Number of Fruit Per Plant

	Full Sun Control	Partial Shade	Full Shade
Melons	100%	110%	50%
Tomatoes	100%	70%	50%

The melons growing in full sun produced slightly less fruit per plant than those in partial shade – but about twice as many as those in full shade.

Tomato fruit-per-plant decreased significantly in both partial and full shade, producing 70% and 50% respectively as compared to full sun.

PLANT QUALITY: The plants grown in full sun suffered a high level of sun damage, while those in partial and full shade were protected from sunburn and showed healthy leaves and fruit throughout the growing season.

HARVEST TIMING: Melons and tomatoes growing in the fully and partially shaded plots were delayed by about 10 days as compared to those in full sun. With the extra time, though, the plants caught up in the number of flowers and fruit the team were tracking over the growing season.

SOIL IMPACTS: Soil moisture remained higher for longer periods of time underneath full shade and decreased with less shade. Additionally, soil temperatures remained uniform during night periods across all plots even though they differentiated during the day – with the full sun soil tending to be about 2℃ hotter than shaded regions.

The key conclusion from this study is that the optimal level of light for melons is less than what the plants receive in full sun. Partial shade can produce larger melons and maintain, or even slightly improve, the number of fruit per plant. Tomatoes, on the other hand, benefit from full sun, given the significant decrease in fruit per plant in both partial and full shade.

Future exploration: Impact of shade on water use

Looking ahead, the researchers are also interested in understanding the impact of shade on water use. In this initial study, the team used sprinkler irrigation to ensure an even application of water in each plot. In future work building on these findings, they will be using a drip irrigation system to enable more precise control and measurement of water use – with an eye toward quantifying the water savings potential of melons and other crops commonly grown in the Central Valley. This trial demonstrated the possibility of water savings due to the increased water retention in shaded regions of the soil, and more careful tracking of water applications will be used in the future.

Implications for Agrivoltaics

The findings of this trial point to the potential benefits of integrating melon production and solar energy production, utilizing partial shade from solar panels to optimize crop yield and quality while also generating renewable electricity. It also points to the opportunity to save water, one of the most important limited resources in the Central Valley.