The French make lavender syrup, which is used to make lavender scones and lavender marshmallows. Fo example lavender oil, was used in World War 1 to disinfect walls and floors of the hospital. As the folk wisdom says, lavender oil is also helpful to headaches when rubbed on your temple. During the Black Plague of the 16th century, lavender oil was used to ward off the dreaded disease. English lavender blooms in late spring to early summer.