OFRF Farmer Led Trials: How Mulch Impacts Soil Moisture in an Organic Vineyard

Jorge Reyes, Reyes Farm

Farm Trial Overview

Jorge proudly comes from a Mexican migrant farmworker family who had a dream of owning a farm one day. After retiring from the Navy, he was able to purchase a 3-acre vineyard located in Potrero, California. Jorge’s young vineyard produces organic grapes, and it is in the process of obtaining organic certification. Jorge plans to produce organic wine.

The challenges on a young vineyard are not in short supply, so Jorge focused on the use of mulch for soil moisture retention, weed management and grape quality. Improving soil moisture is critical to Jorge’s operation, as the irrigation depends on a solar-powered pump. The local climate conditions are generally very dry, with 9 to 11 inches of rain during the winter season. Wildfires are a frequent risk during the dry season, making soil moisture a critical factor and cost to Jorge’s operation.

With OFRF technical support, Jorge conducted a paired comparison where 10 grapevines with mulch were compared with 10 vines with no mulch. Jorge applied 3 inches high of mulch around the vine (about a 4-foot area for each vine) in late May. Over the course of the growing season, Jorge monitored soil moisture levels, weed presence, and grape sugar content (Brix levels).

For full details on the study’s methodology and results, check out the OFRF Farmer Led Trials Blog, or read the final report linked here.

Download Final Report

Funding Amount

$1,500

Funding Year

2024

Location

Potrero, California

Collaborators

Reyes Farm

Organic Farming Research Foundation

Key Findings

  • Increased Soil Moisture: In both Syrah and Viognier grape varieties, mulched plots consistently retained higher moisture levels compared to unmulched plots. This effect was statistically significant in Syrah at all sampling dates and in Viognier at two out of three sampling dates.
  • Reduced Weed Pressure & Labor Needs: Jorge observed fewer weeds in the mulched plots, leading to reduced labor for trimming and vineyard maintenance.
  • Potential Impact on Grape Quality: While not formally evaluated, preliminary Brix readings suggest mulched vines had slightly higher sugar content (22 vs. 20) than unmulched vines, indicating potential effects on fruit ripening.

Encouraged by these results, Jorge plans to integrate mulching as a long-term vineyard management strategy. He is particularly interested in further exploring its impact on grape yield, soil biodiversity, and irrigation efficiency in future seasons.

Region

Western

Topic

Conservation and Habitat, Cropping Systems

Category

Tree and Vine Crops

Year Published

2025