Drainage - This is perhaps the most important factor for successful lavender growing. If planting in heavy or poorly draining soil, dig a hole much larger than the pot size and fill with soil amended with gravel or chicken grit. Make sure water drains readily from the hole before planting. Learn How To Plant Lavender
• Acidity - Lavender likes soil at neutral pH or slightly alkaline. If soils are acidic as is commonly the case here on San Juan Island, they will need amendment - calcitic lime works particularly well in this regard.
• Sun - Lavender likes to have at least eight hours of sun daily during the flowering season. Good sun exposure is important for full blooming and long life. It does especially well when planted near heat-reflecting materials, such as against rock walls, over crushed oyster shells or light colored gravel, etc.
• Weed control - In rich soil, lavender does not compete well with weeds. Make sure the area is well-cleared of weeds before planting, and be vigilant about removing them when they reappear.
• Watering - Over-watering is the most common reason for lavender failing to thrive. In our climate in the San Juan’s, watering is necessary only in the first year when establishing the plants. Make sure the plants neither dry out nor have soggy roots (if using a water meter, water only when “3” or less). Use drip irrigation where possible, or when watering by hand, avoid getting moisture on the leaves. Once plants are established, they should rarely need watering – though watch for early signs of wilting in the early stages of flower-head development when a short watering or two will be beneficial.
• Fertilizing - Except in pots (see below), lavender does not need fertilizer, which contributes mainly to leaf growth, but does little for flowering. Nutrient depletion can also be a source of leaf yellowing.
• Pruning - Pruning is absolutely required for good flower development and to prevent woody stalks. The best time to prune in our climate is late fall. Cut the flowers down to within two leaf nodes above the grey/brown woody part of the stem (leaving approximately 2-3 inches of green stalk). Not cutting down this far can result in the plant becoming leggy over time, or growing so large that with a full flourish of flowers it can become unduly top heavy, leading to the main trunk splitting and potential plant death. On the other hand, cutting too far, namely into the woody part of the stem, can decrease plant life significantly. Learn How To Prune Lavender
• Potted lavender - Lavender grows well in pots as long as there is enough sun and enough room to accommodate the plant’s large root system. If you do plant in pots, use well draining potting soil amended with gravel. Unlike their field-planted brethren, potted plants dry out readily, so in this situation more watering is required. Similarly, in pots lavender may benefit from occasional fertilizing such as with fish emulsion.
If you have some lavender plants that you picked up at your local nursery and you aren't quite ready to plant them yet, learn how to care for lavender before planting.