Growing lavender well starts with planting lavender well.
All types of lavender need full sun to thrive. Lavender is a sun worshiper and can take up to six hours of direct sun daily. The exception is in the Deep South and Southwest, where a little protection from sizzling afternoon sun is welcome.
When planting lavender, you want soil that drains well and is slightly alkaline. Drainage is vital because lavender plants often die from root rot due to soggy soil. In regions where lavender is winter hardy, consider winter drainage, too. Soils that tend to hold water in winter can quickly kill lavender.
To achieve alkaline soil, mix some crushed oyster shell or limestone gravel into planting holes. You might even excavate a slightly deeper planting hole and fill the bottom two-thirds of the space with limestone gravel. This helps improve drainage in heavy soils and provides an alkaline environment for roots. Some gardeners also add a mixture of lime, bone meal and compost to planting holes to get alkaline pH and jump-start growth. Aim for about a half-cup total using equal parts of those items.
Remember that lavender comes from a Mediterranean climate, so it loves heat. Consider planting lavender near a south-facing wall or paved areas to provide reflected heat to plants. Many gardeners mulch around lavender plants using limestone gravel on top of sand. The gravel reflects heat to the plants and brings that alkaline element to soil.
Planting lavender in a mound or raised bed (18 to 24 inches tall) is what most commercial growers do. This technique is especially effective when you garden where summers are hot and humid. In this environment, it’s also wise to leave ample space between plants for air circulation. In general, spacing plants using their height measurement provides sufficient air flow—and a breathtaking show when plants are in bloom.
In Zones 3 to 7, tackle planting lavender in spring after all danger of frost has passed. If you must plant in fall, do so at least eight weeks before the average frost date. Lavender grows fastest in heat, so as temperatures drop in autumn, growth slows down dramatically. Fall-planted lavender needs ample time to develop a sturdy root system to survive winter. In Zones 8 and warmer, planting lavender can be done in spring or fall.
When you’re planting lavender, dig a hole that’s deep enough for the plant’s roots, and tuck the plant into place, snugging soil around it. Take care not to plant lavender more deeply in the ground that it sat in its nursery pot. Prune plants lightly to promote branching. Water until plants show steady new growth. Once established, lavender grows best with neglect.