Ensure the soil surrounding your English lavender is fast-draining, and transplant it if it's in a boggy, wet location or in heavy clay that doesn't drain. All lavenders are highly susceptible to root rot.
Test the soil pH to ensure a level between 6.5 and 7.5. Dig in lime if the soil is too acidic, as lavender requires a slightly alkaline soil.
Prune your English lavender after it blooms, cutting back both the spent bloom stems and the foliage to about two-thirds of the previous length.
Feed your English lavender with an annual top-dressing of compost. Additional fertilizing is unnecessary.
Mulch around your English lavender to suppress weeds. It is important to use a dry, non-absorbent mulch (bark or gravel), and to ensure that you keep a 2-inch wide, mulch-free area around the base of each plant to avoid trapping excess moisture around the shallow roots.
Monitor your English lavender for wilting, a sign that it needs watering. Water your lavender only under the very driest conditions. Lavenders prefer somewhat dry soil and can be devastated by humid, damp or overly wet weather.