Application of Oyster Shell Mulch for Lavender Production

2003 Annual Report for FW01-052

Project Type: Farmer/Rancher
Funds awarded in 2001: $6,000.00
Projected End Date: 12/31/2004
Region: Western
State: Washington
Principal Investigator:
Mike Reichner
WSU Coop Ext.

Application of Oyster Shell Mulch for Lavender Production


Purple Haze Lavender Farm wants to apply oyster shell mulch to row crops of commercial lavender to see if it will help control weeds, conserve water, deal with mildly acidic soils and help the lavender grow in temperatures that are lower than in the herb’s native climate in the Provence region of France. Farm owner Mike Reichner had read about research showing that applying white sand mulch to lavender plants increased flower production 400% and increased quality and quantity of essential oil from the lavender. Reichner postulates that substituting crushed oyster shells for white sand may have a similar effect.

Purple Haze Lavender Farm applied oyster shell mulch on two test plots. The mulch increased flower yield by about 12% but failed to improve the quality of the essential oil distilled from the flowers. The mulch did reduce weeds and conserve water. A second test with increased mulch coverage is currently under way.

Purple Haze Lavender is a 7.5-acre certified organic lavender farm with more than 13,000 lavender plants of 40 varieties. A core of 10 varieties are used for production of fresh and dried bundles for the floral industry, essential oil distillation, retail and wholesale of value-added products and a U-pick business created for the tourist trade.

The first of two test plots involved the species Lavendula intermedia, or Hidcote Giant, to measure the effect on flower production for bundles. The second test was on Lavendula angustifolia, or Royal Velvet, to measure the effect on the quality of essential oil gained through the distillation of the flowers. A 4-inch mulch was applied in 2001 from the plant base to the drip line.

In the 2002 harvest of Hidcote Giant, the mulched plants produced 8.2 bundles per plant while the plants not mulched produced 7.2 bundles, a net increase of 1 bundle per plant. In addition, the oyster mulch significantly reduced the amount of weeding required throughout the season and reduced water needs during the summer months. In the 2002 harvest of Royal Velvet, essential oil samples from both the mulched and unmulched plants were sent for mass spectra analysis to determine the oil profile. No significant differences in oil quality or quantity were seen. But the mulch kept weeding, cultivating and water use to a minimum.

Jadyne Reichner, in the project’s annual report, says that because the hypothesis in the original proposal is based on light units to the plant, she believes that by increasing the mulch area around the plant, the light will be increased as will the flower production. To test that theory, the Reichners have extended the project through the winter of 2002-03, applying the mulch to the entire area between the rows.

“It is our hope that this will result in an even greater increase in flower production for both the Royal Velvet and the Hidcote Giant,” says Jadyne Reichner, who notes that test results will be available after harvest in the summer of 2003.

Given that the Olympic Peninsula of Washington is home to more than 20 lavender farms, success of the oyster mulch approach could have broad impacts on their production and returns.

The growers, in turn, contribute to the agricultural economic base and to the tourist economy through sponsorship of the annual lavender festival, which hosts more than 12,000 visitors. All of the lavender farms are faced with the same issues: weed control, flower production and quality oil. When growing flowers for the floral trade, the size, color and fragrance of the flowers must be maximized to be competitive. To pick up helpful pointers, three Sequim growers visited the Provence region of France.

“It became obvious that the native soils and the intense heat of the region were contributing to a superior quality of lavender and lavender essential oil,” says Mike Reichner. “The application of oyster mulch is our attempt to simulate the growth conditions of lavender’s native habitat.”

Jadyne Reichner points out that the farm is an agri-tourism destination in Washington. More than 100,000 people visited in the summer of 2002 and saw the SARE grant research in progress.

“We have isolated and signed the area, educating thousands of guests about the test plots and using the grant as a topic of discussion in tours and in presentations to local and regional garden,” she says. “The marriage of agriculture and aquaculture has piqued the interest of local and regional factions in our state.”

Indeed, the Washington State University demonstration garden, Robin Hill Farm, has elected to dedicate a section of its farm to oyster shell mulch, the results from which should be available in the summer of 2003.