The effect of organic fertilizers based on seaweed extract were tested on Rosemary and impacts were measured for both yield and oil quality. The plants were grown in a temperature controlled greenhouse (research conditions) and were treated with either seaweed or an inorganic fertilizer of “matching mineral compostion but with no organic matter”.
Treatments were either by spraying the leaves or into the soil.
The leaves were harvested and oil distilled.
Bottom line: “The seaweed treatments caused a significant increase in oil amount and leaf area as compared with both inorganic treatments and the control regardless of application method.”
OK – so get out that seaweed extract. Note this wasn’t my favorite fish emulsion/fertilizer but a different mix.
Here’s the abstract: