Answer: As with all plants, it helps to understand lavender’s natural origins to know what it needs to grow well. Most lavender species (Lavandula spp.) are native to the Mediterranean region, and so they enjoy that kind of climate—also known as a dry-summer subtropical climate. This climate has a relatively wet winter followed by a droughty summer, with temperatures ranging from 32˚F to 80˚F over the course of the year. Coastal central California and Southern California have this type of climate.
General notes for all regions:
In the garden, provide lavenders with full sun and very well-drained soil. To further improve drainage, dig fine gravel or chicken grit into the top 12 inches of soil, or plant your lavender in a raised bed or a mound. Mulch with fine gravel rather than bark or compost. Lavender also grows well in a pot; terra-cotta is the best choice because it allows you to better control soil moisture and it promotes air flow to the roots.
Be careful watering lavender. Overwatering will certainly kill it. Provide enough water to keep the soil evenly moist the first year, while the plant gets established, but then cut back on watering in subsequent years. Apply a balanced fertilizer once in spring for the first three years.
Lavenders by region:
Midwest and Northeast: Areas with cooler, breezier summers will do the best. Grow cultivars of English lavender (L. angustifolia) or lavandin (L. ×intermedia); these are the hardiest options, being winter hardy to USDA Zone 5a. You can try English lavender in Zone 4 if you plant it in a sheltered location and cover it with evergreen boughs in the winter.
Mid-Atlantic and Southeast: Cultivars of Spanish lavender (L. stoechas) will have the most success here, because they have some tolerance for humidity but are also hardy enough for a Zone 8 winter.
Gulf States: Spanish, fernleaf (L. multifida) and French and French hybrids (L. ×allardii, L. dentata, L. ×heterophylla) are the most tolerant of the humidity found here. These are all hardy to Zone 8 or 9.
West: Lavenders generally do well here. In areas that receive much winter rain, pay special attention to soil drainage.
In any humid area, be sure to leave at least three feet between lavender plants; this will allow for good air flow and help prevent fungal diseases.