Lavandula x intermedia is a hybrid cross between English Lavender and Portuguese Lavender. They are somewhat less hardy, but grow larger and will produce more flower spikes. They also tend to bloom later than other Lavandula species, blooming from July to September. It will go to seed from August to October.
Lavender demands water only during the first weeks after planting, during high heat periods, and even more often if it's potted.
Cut back the flower stalks after they have finished, and then trim back plants in April, if necessary.