Lavender, with its fragrant foliage and purple flower spikes, is a popular choice for gardens. Native to the Mediterranean region, it thrives in conditions that mimic its origins: hot sun, excellent drainage, and lean, rocky soil. These naturally low-fertility conditions mean the plant requires minimal nutrients for healthy growth. Understanding this preference for poor soil is key to successful cultivation.
Assessing the Need for Fertilization
Established lavender plants growing in the ground usually do not need fertilization. Too much fertilizer, particularly one high in nitrogen, can be detrimental to the plant’s health. Overfeeding leads to excessive leaf and stem growth, often called “legginess,” at the expense of flower production and essential oil concentration.
Fertilization is generally only necessary in specific situations. Container-grown plants require light feeding because the limited soil volume is quickly depleted of nutrients through watering and leaching. A sparse application may also be beneficial if the in-ground soil is extremely sandy and nutrient-depleted. Signs that a plant needs a boost include noticeably poor growth, pale leaves, or a significant reduction in flowering.
Selecting the Right Fertilizer Type
When fertilization is necessary, focus on a low-nitrogen formula. Since nitrogen promotes foliage, a high concentration encourages leafy growth instead of fragrant blooms. Look for a fertilizer where the phosphorus (P) and potassium (K) content is equal to or higher than the nitrogen (N) content.
A commonly recommended NPK ratio is a balanced, low-nitrogen blend such as 5-10-10 or 5-15-10. Phosphorus supports strong root development and flower bud formation, while potassium enhances overall plant strength and essential oil quality. Slow-release granular products are preferred because they deliver nutrients gradually, mimicking the plant’s need for sustained, gentle feeding.
Organic amendments can also supply gentle nutrients and improve soil structure. A light application of well-rotted compost in the spring provides a slow, steady release of micronutrients. Bone meal is a natural source of phosphorus, which can be sparingly incorporated into the soil to support flowering and root health. Lavender prefers a slightly alkaline soil (pH 6.5 to 8.0), and adding garden lime to acidic soils helps raise the pH, making micronutrients more accessible.
Timing and Application Methods
The optimal time to fertilize lavender is once a year, in early spring, just before the plant begins new growth. This timing provides nutrients for the upcoming growing and blooming season. Avoid fertilizing late in the year, particularly after mid-summer, as late-season feeding encourages tender new shoots vulnerable to frost damage.
For in-ground plants, apply a granular or slow-release fertilizer lightly around the plant’s drip line. Keep the fertilizer several inches away from the woody crown and stem to prevent potential root or stem burn. After application, lightly scratch the fertilizer into the top layer of soil and water it in.
Lavender grown in pots requires a different approach due to the risk of nutrient buildup. Use a diluted liquid fertilizer, applied at half or even quarter the strength recommended on the package. Apply this liquid feed directly to the soil, ensuring the plant receives a mild, manageable boost without the risk of over-fertilization.