Lavender (Lavandula spp.) is a useful garden plant, brightening the summer garden with its fragrant blue spikes. Many gardeners dream of growing lush mounds of it. Unfortunately, lavender has a reputation for being prone to fungus, so many gardeners stay away from it. Lavender is indeed prone to various soil-borne fungi, but proper culture can greatly mitigate the problem.
Lavender requires full sun and well-drained soil. It can tolerate partial shade, but only if it gets four hours or more of bright sun in the afternoon. Sun dries out wet leaves and soil, reducing the likelihood of fungal problems. Planting on a slope increases drainage. Give lavender enough room to grow to its full potential so other plants don’t encroach upon it.
Native to the Mediterranean, lavender does best in poor, rocky soils which drain freely. When planting, dig a hole about 12 inches deep and wide and mix in about half sand or pea gravel. If planting in clay, add about one-quarter compost, removing the clay to another part of the garden. Adding bonemeal when planting neutralizes acidic soils and facilitates strong root growth.
Water is the enemy of lavender. Water at the plant’s base, not overhead. Overhead watering splashes soil-borne fungus onto the plant, causing disease. An inch of pea gravel mulch will help prevent splashing during rainfall. Water only while the plant is becoming established and during periods of extreme drought.
Lavender requires poor soil, so fertilization should be a rare event. When needed, using a slow-release, organic fertilizer in minimal quantities helps prevent root burning and over-feeding.
Cut back lavender plants about one-third to one-half in early spring. This will allow your lavender to branch out and become fuller. It also keeps the plant from becoming top-heavy and falling on the ground, putting the leaves in contact with the soil. Likewise, remove spent flower spikes in summer. Replenish pea gravel mulch as needed. Discard cuttings, as they might have fungus.