Plant problems

Why Are My Parahebe Leaves Curling?

Q: Why are my parahebe leaves curling?

Parahebe leaves curl most commonly in UK gardens because of waterlogging and root rot in wet, poorly drained conditions (parahebe comes from rocky, freely draining habitats in New Zealand and Australia and does not tolerate consistently wet soil), cold damage in hard UK winters (most parahebe species are only moderately hardy and the small, semi-evergreen or evergreen leaves curl and brown after hard frost), or drought stress in very freely draining, shallow soils during summer. Parahebe is a genus of small to medium-sized sub-shrubs and perennials from New Zealand, Australia, and New Guinea; they are closely related to Hebe and Veronica and produce similar small, five-lobed flowers in white, pink, lilac, or pale blue from summer into autumn. The most commonly grown species in UK gardens are Parahebe catarractae (New Zealand parahebe), which produces white or pale pink flowers with a purple or crimson eye in June to September on neat, low mounds of small, toothed, semi-evergreen leaves; Parahebe perfoliata (digger's speedwell), a more unusual, upright Australian species with grey-blue, stem-clasping leaves and lavender-blue flowers; and various named cultivars of hybrid origin. Parahebe catarractae and its cultivars (such as 'Delight', with white flowers and a pink eye) are particularly well suited to rock gardens, raised beds, and the front of well-drained borders in UK gardens; the combination of compact, low habit, freely draining growing medium, and good sun exposure suits these plants perfectly. The plants are moderately hardy in the UK; they are typically hardy to about -8 to -12°C in freely draining conditions but are much less tolerant in wet, cold soil.

Q: Is parahebe hardy in the UK?

Parahebe hardiness in the UK varies by species; most commonly grown forms are moderately hardy, surviving to about -8 to -12°C in freely draining conditions. Parahebe catarractae and its cultivars are the most widely grown and are reliably perennial in most of England and Wales in well-drained, sheltered conditions; they may be damaged or killed in hard winters below -12°C, particularly in wet soil. Parahebe perfoliata (digger's speedwell) is considered somewhat less hardy and is most reliable in the milder parts of the UK (south-west England, mild coastal gardens, sheltered urban positions). The key to maximising parahebe hardiness in the UK is excellent drainage: plants in rocky, freely draining, slightly alkaline soil survive temperatures that would kill the same plants in wet, clay soil. The combination of cold and wet is far more damaging than cold alone. A position in a rock garden, raised bed, or scree garden with gritty, freely draining growing medium in full sun provides ideal winter survival conditions. In very cold UK areas (north of England, Scotland, high altitude), parahebe can be grown as a container plant overwintered under glass; the compact, spreading habit of most species suits container culture well. Parahebe is generally more cold-tolerant than many other New Zealand native shrubs (such as tender hebe cultivars) and provides a reliable mid-summer flowering display in positions where the drainage is adequate.

Q: How do I grow parahebe in the UK?

Parahebe grows best in full sun in well-drained to very freely draining, moderately fertile, neutral to slightly alkaline soil; the rock garden, raised bed, scree garden, or front of a well-drained border are ideal positions. The plants come from rocky, high-altitude or coastal habitats in the Southern Hemisphere where drainage is excellent and the soil is relatively lean; replicating these conditions in UK gardens is the key to long-term success. Prepare the growing area with generous quantities of coarse grit (at least 30% by volume in heavy or clay soils) to improve drainage; a raised bed with a gritty growing medium is ideal in wetter UK areas. Avoid planting in heavy clay, low-lying, or poorly drained soils; waterlogging is the most common cause of parahebe death in UK gardens. Plant in spring (April to May) after the last hard frost. Parahebe does not need regular feeding; a light application of a balanced fertiliser in April is sufficient. Cut back the previous year's flowered stems in March to April to encourage compact new growth; the plants can become woody and bare at the base over time without regular trimming. Propagate by semi-ripe cuttings in July to August; cuttings root readily in a gritty compost under a cold frame or on a warm windowsill, and it is prudent to keep a few young plants as insurance against winter losses. The flowering period is long (June to September) and the plants are attractive to bees and other pollinators throughout.

Q: What is the difference between parahebe and hebe?

Parahebe and Hebe are closely related genera in the plantain family (Plantaginaceae); both originate primarily from New Zealand and produce small, five-lobed, tubular flowers in racemes. The distinctions between them are largely botanical: in general terms, parahebe species tend to be lower-growing, more spreading or mat-forming sub-shrubs or perennials rather than the more distinctly shrubby habit of most hebes; parahebe leaves are typically smaller, more toothed, and more herbaceous in texture than the thick, leathery leaves of many hebe species; and parahebe flowers are often produced singly from leaf axils rather than in the dense, bottlebrush-type racemes of large-flowered hebe cultivars. In terms of garden use, parahebe is best treated as a rock garden or front-of-border plant for well-drained, sunny conditions rather than as a specimen shrub; the scale and habit of parahebe is closer to a perennial than a shrub. The cultural requirements of parahebe and many hebe species are similar: full sun, freely draining soil, moderate fertility, and protection from cold wet soil in winter; both are more cold-tolerant in dry conditions than in wet ones. Note that taxonomic changes have recently merged many former Parahebe species into Veronica or Hebe depending on the authority followed; in UK garden centres, plants may be sold under any of these names, and the cultural guidance given for parahebe applies broadly to these reassigned species as well.

Parahebe is a genus of low-growing sub-shrubs from New Zealand and Australia, closely related to Hebe, with small flowers in white, pink, or lavender from June to September. The plants need freely draining, lean soil in full sun; waterlogging in wet UK winters is the most common cause of plant death. The rock garden, raised bed, or scree is the ideal UK position.

Waterlogging

Waterlogging is the most common cause of parahebe failure in UK gardens; the plants come from rocky, freely draining habitats and their roots rot rapidly in saturated, poorly aerated conditions. Affected plants collapse suddenly, with leaves that yellow, curl, and drop; the stems collapse and the plant cannot be revived once the root rot has progressed. The problem is most acute in heavy clay soils, in low-lying positions where water pools, and in UK winters with prolonged wet spells where the soil remains saturated for days or weeks at a time.

What to do

Plant only in freely draining to very freely draining soil; add generous quantities of coarse grit (30% by volume) to improve drainage in heavier soils. A raised bed, rock garden, or scree filled with gritty growing medium provides the ideal winter drainage. Do not plant in low-lying or clay-heavy positions. Apply a coarse grit top-dressing around the base of the plant to improve drainage at the root collar zone in winter and prevent crown rot.

Cold damage

Cold damage browns and curls the semi-evergreen leaves of parahebe in hard UK winters; temperatures below -10 to -12°C cause the leaves to curl and turn grey-brown. Plants in freely draining soil survive significantly lower temperatures than those in wet conditions; the frost-hardiness figures for parahebe assume good drainage. Cold wind can also cause desiccation of the small leaves, producing browning similar to frost damage. In hard winters, parahebe may be cut back to the base but typically regrows from the woody rootstock if drainage has been adequate.

What to do

Ensure excellent drainage before winter; this is the most important factor in frost survival. Wrap pot-grown plants in bubble wrap or move under glass for the coldest months. In the garden, a winter covering of dry straw, pine boughs, or horticultural fleece provides some frost amelioration. Take insurance cuttings in July to August (semi-ripe cuttings root readily in gritty compost); young plants overwinter well on a frost-free windowsill and can replace winter casualties.

Drought stress

Parahebe tolerates dry conditions better than most sub-shrubs once established in well-drained soil; the leaves are small and the plants are adapted to rocky, exposed habitats where soil moisture is limited. However, in very shallow, freely draining soil or rocky scree, the leaves can curl and the plants look stressed in prolonged hot dry spells. Container-grown parahebe dries out quickly and can suffer drought stress within a day or two of the compost becoming dry in warm weather.

What to do

Established parahebe in the ground rarely needs supplementary watering in average UK conditions; occasional deep watering during prolonged dry spells in summer is sufficient. Container-grown plants need regular checking in warm weather; water when the top 2 to 3 cm of compost is dry. The plants recover quickly from moderate drought stress once watered; the small leaves unfurl within hours of the root zone being moistened.

Frequently asked questions

Why are my parahebe leaves curling?

Parahebe leaves curl most commonly because of waterlogging in wet UK conditions (the plants rot rapidly in saturated soil; plant in freely draining gritty medium), cold damage in hard winters (leaves brown and curl below -10°C; drainage significantly improves cold tolerance), or drought stress in very shallow or freely draining soil or containers (the small leaves curl in prolonged dry spells; water and they recover within hours). Freely draining, lean soil in full sun resolves most problems.

Is parahebe hardy in the UK?

Most commonly grown parahebe species are hardy to about -8 to -12°C in freely draining conditions and are reliably perennial in most of England and Wales in a rock garden, raised bed, or scree. In wet soil, cold tolerance is significantly reduced. Take insurance cuttings in July to August (semi-ripe cuttings root readily) as winter insurance. Container plants can be brought under glass for the coldest months.

How do I grow parahebe in the UK?

Grow in full sun in very well-drained, moderately fertile, neutral to slightly alkaline soil; the rock garden, raised bed, or scree are ideal. Add grit generously to heavier soils. No regular feeding needed; a light balanced feed in April is sufficient. Cut back flowered stems in March to April to maintain compact habit. Take semi-ripe cuttings in July to August as winter insurance. The plants flower from June to September and are attractive to bees throughout.

What is the difference between parahebe and hebe?

Parahebe species are generally lower-growing, more spreading sub-shrubs or perennials with smaller, more toothed leaves and flowers produced singly from leaf axils, rather than the more distinctly shrubby habit and dense bottlebrush racemes of large-flowered hebes. Garden use and cultural requirements are similar: full sun, freely draining soil, moderate fertility. Note that recent taxonomy has reassigned some parahebe species to Veronica or Hebe; plants may be sold under any of these names in UK garden centres.