English lavender

Identification and origin

Lavandula angustifolia belongs to the mint family, Lamiaceae, alongside rosemary and sage. It is native to Spain, France, and Italy, and has naturalized as far as Great Britain, central Europe, and North America.

This evergreen shrub forms a rounded mound, woody at the base, 12 in – 2 ft tall and 2–3 ft wide; it can live ten to fifteen years.

The opposite, narrow leaves, 0–1 in long, have rolled-under edges and a fine gray-green to bluish down; they smell strongly when bruised. In summer, long bare stalks carry dense 1–3 in spikes of small two-lipped flowers, usually lavender-purple, sometimes pink or white, which bees and butterflies visit eagerly. This species yields true lavender oil; the dried flowers scent sachets and potpourri and are used sparingly in cooking.

Common cultivars: ‘Hidcote’, compact and silver-gray with deep purple flowers; ‘Munstead’, compact and greener with lavender-blue flowers; ‘Twickel Purple’, with long, dark, heavily scented spikes; and ‘Lady’ and ‘Mini Blue’, both well suited to growing from seed. Lavandins (Lavandula × intermedia), hybrids with spike lavender (Lavandula latifolia), are more vigorous but somewhat less cold-hardy.

Light

Lavender demands full sun: at least six to eight hours of direct sunlight a day. In shade it gets leggy, flowers poorly, and declines quickly. Choose a warm spot facing south, east, or west, with good air movement, which helps prevent foliage diseases.

Watering

During the first growing season, water regularly whenever the soil surface dries out, especially in hot, dry weather. Once established in the ground, lavender is very drought tolerant and rarely needs watering except in severe drought; in very hot climates, a few deep waterings while flower buds are forming do encourage more blooms.

Potting mix in containers dries out fast: in summer, water once the upper layer of mix has dried, then let it dry again. In winter, keep pots on the dry side and sheltered from heavy rain, for example at the foot of a wall. Too much water is far more dangerous than too little, because it leads to root rot.

Potting mix

It needs lean to moderately fertile soil that is light, sandy, gravelly, or chalky, with a neutral to slightly alkaline pH (about 6.5 to 7.5). Lavender dies out in heavy clay and in any soil that stays waterlogged. On heavy ground, plant it on a mound or in a raised bed 8–12 in high. A mineral mulch such as gravel or stone keeps the crown dry; avoid thick mulches that hold moisture.

In containers, use a pot 12–16 in across with drainage holes and a peat-free, loam-based mix with coarse grit added, up to a quarter of the volume.

Fertilizer needs are low: soil too rich in nitrogen produces lots of leaves, few flowers, and plants more prone to disease and cold injury. A little compost at planting time is enough.

Temperature

This is the most cold-hardy lavender. It is grown in the ground in USDA zones 5a to 9b and tolerates frosts down to about 5 °F in well-drained soil. Soggy soil and repeated freeze-thaw cycles kill it far more often than cold itself. In cold regions, a light mulch of evergreen boughs or straw, laid once the ground has frozen, protects the crown without smothering it.

Roots in containers are less insulated: in winter, shelter pots at the base of a wall, under an overhang, or in a cold frame.

Repotting

Plant in spring as the soil warms, at the same depth as in the nursery pot, spacing plants 18 in – 2 ft apart, or 12–18 in for an edging. Do not plant in winter: young plants rot in cold, wet soil. Fall planting works if about two months of mild weather remain.

Lavender kept in a container blooms better if it is moved each spring into a slightly larger pot with fresh, coarse potting mix.

Pruning

Without pruning, lavender turns woody and opens up in the center. Trim it every year right after flowering, in late summer, removing the spent stalks and about 1 in of leafy growth. In spring, once new shoots appear, remove dry or frost-damaged stems. Do not cut back in fall, and never cut into bare old wood: lavender rarely regrows from it.

Propagation

Cuttings are the most reliable method and come true to the cultivar. From early to midsummer, take non-flowering side shoots, preferably from a young plant. Cut just below a node, strip three or four lower leaves, dip the end in rooting hormone, and insert the cutting in light, moist potting mix kept warm, around 70 °F. Roots form in about a month. Hardwood cuttings taken after flowering, in late fall, also work.

Seed is slower and less even. Chill the seeds in a moist medium in the refrigerator, at about 39 °F, for two to four weeks, then sow them on the surface at 64–70 °F. Germination takes two to four weeks, and seedlings vary in habit and color.

Common problems

• Plant dying back: root rot caused by heavy soil, poor drainage, or overly frequent watering.
• Spots on leaves: diseases encouraged by humidity and poor air circulation; space plants farther apart.
• Few flowers: not enough sun, or too much nitrogen fertilizer.
• Winter losses: soggy soil, repeated freezing and thawing, or an unprotected container.
• Pests: aphids, spittlebugs (frothy masses on stems), rosemary beetle, and leafhoppers; damage is mostly cosmetic and a strong spray of water is often enough. Grasshoppers and deer can also feed on the plants.
• Xylella fastidiosa bacterium: lavender is a high-risk host; buy plants from a reliable supplier.

The same symptom can have several causes: look at exposure, drainage, watering, and recent weather together before acting.

Toxicity

Lavender is toxic to dogs, cats, and horses. It contains linalool and linalyl acetate; eating it can cause nausea, vomiting (except in horses), and loss of appetite. The toxicity is considered low, and the plant does not cause contact dermatitis. If an animal eats some, contact a veterinarian.