Stachys, whether the silver-leaved lamb's ear (Stachys byzantina) or the ornamental betony (Stachys macrantha), is a tough and drought-tolerant perennial, but curling leaves signal a problem worth diagnosing. Overwatering and root rot are the most frequent culprits since stachys hates wet roots, but spider mites, powdery mildew, aphids, and frost damage can all cause similar symptoms. Match what you see to the correct cause before acting.
1. Overwatering and root rot
Stachys originates from dry Mediterranean hillsides and is extraordinarily sensitive to poorly drained or constantly wet soil. Overwatering is the most common mistake gardeners make with this plant, and it is the leading cause of curling leaves followed by complete collapse. When roots sit in saturated soil they are starved of oxygen and quickly colonised by Phytophthora or Pythium pathogens. The dead roots can no longer supply water to the leaves, which curl and yellow even though the surrounding soil is wet. The silver hairy leaves of lamb's ear are especially prone to rotting when water collects at the base of the leaf rosette.
What to look for
- Leaves curling inward and turning yellow, starting at the outer rosette
- Soil remaining wet for days between watering
- Roots brown, mushy, and with an unpleasant smell
- Base of stems or crown soft and discoloured
- Problem worse in clay soil or in low areas where water collects
How to fix it
Reduce watering immediately. If drainage is the underlying problem, lift the plant, improve the bed with coarse grit and gravel, and replant. Cut away any rotted crown tissue with a clean knife, dust with sulphur powder or cinnamon, and allow the plant to dry slightly before replanting. Stachys grown in heavy clay reliably struggles: raise the bed by 10 to 15 cm above surrounding soil level, or grow the plant in containers with a gritty, free-draining compost mix. Water only when the soil is dry an inch below the surface, and never water in autumn or winter unless the plant is in a pot under cover.
2. Spider mites
Spider mites thrive on stachys during hot, dry summers, feeding on the underside of leaves and extracting the cell contents. The damage causes individual cells to collapse, and as the leaf tissue dries and loses structural support the margins curl upward. The fine silver hairs on lamb's ear can make early mite infestations harder to spot than on smooth-leaved plants, so look carefully on the lower leaf surface and between the hairs.
What to look for
- Leaf margins curling upward, especially on newer growth
- Upper leaf surface with a speckled, bronze, or washed-out look
- Fine silky webbing on the underside or between leaves
- Tiny moving dots visible on the leaf underside with a hand lens
- Symptoms worst in hot dry spells with no rain
How to fix it
Blast the undersides of leaves with a strong jet of water on two or three consecutive days to dislodge mites mechanically. Where populations are heavy, apply insecticidal soap or a neem-based spray, covering the leaf underside thoroughly. Predatory mites (Phytoseiulus persimilis) offer excellent biological control in sheltered conditions. Avoid overhead irrigation in hot weather as it creates warm, still humidity that can favour other problems, but boosting air movement around the plant reduces mite populations significantly. Healthy, unstressed stachys plants are more resistant: avoid drought stress and high-nitrogen feeds that produce soft, vulnerable growth.
3. Powdery mildew
Powdery mildew can infect both lamb's ear and betony, causing leaf margins to curl and cup as the fungal mycelium disrupts cell expansion. On the silver-leaved forms, the white fungal coating can be difficult to distinguish from the natural silver hair, so look for the coating on betony or on the green parts of the stem and flower stalks. Conditions that favour infection include warm days, cool humid nights, and poor air movement between crowded leaves.
What to look for
- White or pale grey powdery patches on leaves and stems
- Leaf margins curling or cupping upward
- Leaves appearing distorted or puckered
- Worst in late summer on crowded clumps
- Affected tissue eventually yellows and dries
How to fix it
Cut the plant back hard to just above the crown, removing all infected growth. Stachys responds well to a midsummer cutback and will flush fresh, healthy foliage within two to three weeks. Thin congested clumps by dividing every two to three years to improve airflow through the planting. Avoid feeding with high-nitrogen fertilisers that produce soft, disease-prone growth. Water at the base rather than overhead, and water in the morning rather than the evening.
4. Aphids
Aphids occasionally target the soft growing tips of stachys in spring and early summer, clustering on new unfurling leaves and feeding on the sap. Their feeding, combined with the toxins they inject into the plant tissue, prevents cells from expanding normally. New leaves emerge curled, cupped, or puckered and remain distorted even after the aphids are removed because the damage occurred during cell development.
What to look for
- Soft green or black aphids clustered at the growing tip
- New leaves curling, cupping, or failing to open fully
- Sticky honeydew coating leaves and stems
- Ants farming aphids on the plant
- Damage concentrated on the newest growth
How to fix it
Knock aphids off with a firm water jet or pinch out the infested growing tip if the colony is isolated. Ladybirds, lacewings, and parasitic wasps will control light infestations naturally if you avoid broad-spectrum insecticide sprays. Insecticidal soap applied directly to the colony is effective for heavier infestations without harming beneficial insects once dry. The distorted leaves that formed during the infestation will not straighten but new growth afterwards will be normal.
5. Drought after transplanting
Established stachys is remarkably drought-tolerant, but newly planted or recently divided plants have not yet developed the root system needed to cope with dry conditions. Transplanting or dividing in spring followed by a warm dry spell can cause leaves to curl as the plant struggles to draw enough moisture from its limited root zone. This is temporary and resolves once the plant establishes, but can be severe enough to cause significant leaf drop if ignored.
What to look for
- Leaf curling within days to weeks of transplanting or dividing
- Soil dry below the surface near the root ball
- Outer older leaves most affected
- Plant otherwise looking healthy with no pest or disease signs
- Recovery visible within hours of watering
How to fix it
Water newly transplanted stachys thoroughly at planting, and again every three to four days for the first three to four weeks until the roots spread into the surrounding soil. Once the plant shows signs of active new growth, you can reduce watering to once a week and then to natural rainfall. Transplanting in autumn or early spring when temperatures are lower reduces the transplant stress significantly. A temporary mulch of bark chip or gravel around the plant helps retain moisture during establishment without keeping the crown too wet.
6. Frost damage
Stachys byzantina is reasonably hardy, but an unexpected late frost after new growth has emerged can cause the soft unfurling leaves to freeze and curl. The damage is often cosmetic: the existing growth looks curled and blackened at the tips but the plant pushes fresh leaves from the base once temperatures stabilise. Betony (Stachys macrantha) is similarly hardy but its larger, smoother leaves show frost scorch more dramatically.
What to look for
- Leaf tips or margins curling and turning brown or black after a cold night
- Damage appears suddenly following a frost event
- Outer and uppermost leaves most affected
- Crown and base of plant appear unharmed
- New growth emerging from the crown looks healthy
How to fix it
Leave frost-damaged foliage in place until all risk of further frost has passed: it provides some insulation for the crown below. Once the risk has gone, cut back the damaged leaves to healthy tissue just above the crown. New growth will emerge within two to three weeks. If late frosts are common in your area, avoid cutting stachys back in early spring and instead wait until mid-spring. Covering plants with a double layer of horticultural fleece on forecast frost nights protects the emerging growth without trapping moisture.
Quick diagnosis checklist
| What you see | Most likely cause | First action |
|---|---|---|
| Leaves curl and yellow, soil wet, roots mushy | Overwatering / root rot | Reduce watering, improve drainage, replant |
| Margins curl up, bronze speckling, fine webbing | Spider mites | Water jet to undersides, insecticidal soap |
| White powder, leaf margins cupping | Powdery mildew | Cut back hard, improve airflow |
| New tips curled, aphids visible, sticky residue | Aphids | Knock off with water, insecticidal soap |
| Curling after recent transplanting, soil dry | Transplant drought | Water thoroughly, mulch lightly |
| Tips blackened and curled after cold night | Frost damage | Leave until frost risk passes, then cut back |
Frequently asked questions
Why are my stachys leaves curling and going yellow?
Curling combined with yellowing on stachys almost always points to overwatering or waterlogged soil. Stachys is a Mediterranean plant adapted to dry, well-drained conditions and its roots rot quickly in persistently wet soil. Reduce watering, improve drainage, and check that the root zone is not sitting in water.
Can spider mites curl stachys leaves?
Yes, especially in hot dry summers. Spider mites feed on the underside of stachys leaves, extracting cell contents and causing the tissue to dry out and curl. Look for fine webbing on the leaf underside and a speckled or bronzed look to the upper surface. Spray with a strong water jet or apply insecticidal soap.
Why do stachys leaves curl in summer?
Summer curling on stachys is usually caused by spider mites or, in humid conditions, powdery mildew. Both problems worsen in hot weather. Check the leaf undersides for mites or webbing, and the upper surface for white powdery coating. Unlike drought-sensitive plants, stachys handles dry heat well and rarely curls from drought alone.
Should I cut back curling stachys leaves?
Yes. Cutting stachys back hard in midsummer refreshes the plant, removes diseased or pest-damaged foliage, and encourages a flush of fresh silver growth. Cut the whole clump to within a few centimetres of the ground, water once if the soil is dry, and new leaves will appear within two to three weeks.