Coral Bells Plant Uk

Coral bells (Heuchera) are versatile perennials perfect for UK gardens, offering vibrant foliage colour from spring through winter. This complete guide covers everything from choosing the best varieties for British conditions to planting, maintenance, and solving common problems for thriving plants year after year.

Key Takeaways

• Perfect for UK climate: Coral bells plant UK gardens thrive in our temperate conditions with proper drainage and partial shade
• Year-round interest: Evergreen foliage provides colour through winter when most plants die back
• Choose the right variety: Dark-leaved types tolerate more sun; light-leaved varieties need more shade protection
• Plant in autumn or spring: These seasons give roots time to establish before extreme temperatures arrive
• Divide every 3-4 years: Regular division prevents woody centres and keeps plants vigorous and healthy
• Watch for vine weevil: This is the main pest threat in UK gardens – check roots regularly for grubs
• Great companion plants: Pair with ferns, hostas, and spring bulbs for stunning shade garden combinations

Quick Answers to Common Questions

When is the best time to plant coral bells in the UK?

Autumn (September-October) is ideal for planting coral bells in the UK, as warm soil encourages root establishment before winter. Spring (March-April) is the second-best option.

Do coral bells prefer sun or shade in UK gardens?

Most coral bells prefer partial shade or dappled light. Dark-leaved varieties tolerate more sun (up to 6 hours), while light-leaved varieties need protection from hot afternoon sun.

How often should I divide my coral bells plants?

Divide coral bells every 3-4 years in spring or autumn when the centre becomes woody and flowering declines. This rejuvenates the plant and gives you free new plants.

What is the main pest problem for coral bells in the UK?

Vine weevil is the most serious pest. Adult beetles notch leaves, but larvae cause fatal damage by eating roots. Check plants regularly and use nematode biological control in late summer.

Can I grow coral bells in containers on a UK patio?

Yes, coral bells excel in containers. Use a 30cm+ pot with free-draining compost, position in morning sun or dappled shade, water regularly, and feed every 2-3 weeks during the growing season.

Why Coral Bells Are a UK Garden Favourite

If you walk through any British garden centre in spring, you will spot coral bells plant UK displays front and centre. These remarkable perennials have earned their popularity honestly. They offer something few other plants can match: stunning foliage colour that persists through every season, even the greyest British winter.

Native to North America, Heuchera has adapted beautifully to our climate. The plant forms neat mounds of ruffled leaves in shades that range from deepest purple-black through caramel, lime green, silver, and fiery orange. In early summer, delicate bell-shaped flowers rise on wiry stems above the foliage, attracting bees and adding a second layer of interest. For UK gardeners seeking low-maintenance impact, coral bells deliver exceptional value.

Understanding the Coral Bells Plant Family

What Exactly Are Coral Bells?

Coral bells belong to the genus Heuchera, part of the Saxifragaceae family. The common name comes from the tiny bell-shaped flowers that appear in late spring to early summer. However, modern breeding has shifted focus dramatically. Today, most gardeners grow coral bells plant UK varieties primarily for their foliage rather than their blooms.

The species Heuchera sanguinea produces the classic coral-red flowers that gave the plant its name. But breeders have crossed this with other species like Heuchera americana, Heuchera villosa, and Heuchera micrantha. The result is an astonishing array of cultivars with leaves in nearly every colour imaginable. Some varieties even change colour through the seasons, offering a dynamic display that evolves month by month.

Species and Hybrids Suited to British Gardens

Not all Heuchera perform equally well in UK conditions. The villosa hybrids, with their larger, hairier leaves, handle our humidity and heat waves better than many older types. The americana hybrids offer excellent cold tolerance and striking silver veining. Micrantha hybrids tend to be more compact, ideal for containers and small spaces.

When shopping for coral bells plant UK nurseries stock, look for varieties bred specifically for British conditions or those with Award of Garden Merit (AGM) status from the RHS. This award indicates reliable performance in UK gardens after extensive trialling. Varieties like ‘Palace Purple’, ‘Obsidian’, ‘Lime Rickey’, and ‘Caramel’ have all proven themselves across diverse British growing conditions.

Choosing the Best Varieties for Your UK Garden

Dark-Foliaged Varieties for Drama

Deep purple, near-black, and rich chocolate varieties create stunning contrast in the garden. ‘Obsidian’ holds its jet-black colour exceptionally well, even in summer heat. ‘Palace Purple’ was one of the first dark varieties widely available and remains a reliable performer. ‘Blackberry Crisp’ offers ruffled edges that catch light beautifully. These darker types generally tolerate more sun than lighter varieties, making them versatile for different garden positions.

Plant dark coral bells plant UK varieties where they catch morning or evening light. The sun illuminates the leaf texture and reveals subtle undertones that disappear in deep shade. They pair brilliantly with golden grasses, yellow-flowered perennials, or silver-leaved plants like Artemisia or Stachys.

Lime and Chartreuse Varieties for Brightening Shade

Few plants light up a shady corner like lime-green Heuchera. ‘Lime Rickey’ AGM produces vibrant electric-green foliage that practically glows in low light. ‘Electric Lime’ offers similar impact with larger leaves. ‘Key Lime Pie’ has a more mounded habit and ruffled edges. These varieties need more shade protection than dark types – afternoon sun will scorch their leaves, especially during hot UK summers.

Use lime coral bells plant UK selections to highlight pathways, edge woodland borders, or brighten containers in shaded courtyards. They work beautifully with blue hostas, purple ferns, and white-flowered shade plants like Tiarella or Brunnera.

Caramel, Peach, and Amber Tones for Warmth

The ‘Caramel’ AGM variety revolutionised Heuchera breeding with its unique amber-caramel foliage that shifts through peach, gold, and bronze tones across seasons. ‘Georgia Peach’ offers larger leaves with a strong peach colour and silver overlay. ‘Marmalade’ displays ruffled leaves in rich amber with pink undersides. These warm-toned varieties bridge the gap between sun and shade tolerance, performing well in dappled light or morning sun.

These varieties shine in autumn when their colours echo the changing leaves of deciduous trees. Plant them where you can appreciate the seasonal transition. They combine beautifully with ornamental grasses, sedums, and late-flowering perennials like Japanese anemones.

Silver and Pewter Varieties for Sophistication

Silver-leaved Heuchera bring elegance to any planting scheme. ‘Silver Scrolls’ AGM shows pewter-silver leaves with dark veining and purple undersides. ‘Frosted Violet’ offers silver-frosted purple leaves. ‘Cinnabar Silver’ has striking silver foliage with red flowers – a rare combination. These varieties thrive in shade where their metallic sheen catches available light.

Silver coral bells plant UK choices work wonderfully in contemporary garden designs. Pair with black mondo grass, white-flowered plants, or dark-leaved companions for high-contrast modern schemes. They also excel in container displays where their refined foliage can be appreciated up close.

Planting Coral Bells in UK Gardens

When to Plant for Best Results

Timing matters significantly for coral bells plant UK establishment. Autumn planting (September to October) is ideal. The soil remains warm from summer, encouraging root growth before winter. Plants establish quietly underground, ready to burst into growth when spring arrives. Spring planting (March to April) works well too, but you must water diligently through the first summer as roots are not yet deep enough to withstand dry spells.

Avoid planting in summer heat or winter cold. Summer planting stresses plants during establishment. Winter planting risks root rot in cold, wet soil. If you buy plants in summer, keep them in pots in a sheltered spot until autumn. If you buy in winter, pot them up and keep in a cold frame or unheated greenhouse until spring.

Selecting the Perfect Site

Most coral bells plant UK varieties prefer partial shade – morning sun with afternoon shade, or dappled light beneath deciduous trees. Dark-leaved varieties tolerate more sun (up to 6 hours in UK conditions). Light-leaved varieties need protection from hot afternoon sun. All types struggle in deep, dry shade beneath evergreens or against north-facing walls where light levels are too low.

Consider the microclimate of your chosen spot. South-facing walls create heat pockets that may scorch leaves. Frost pockets in low-lying areas can damage emerging spring growth. Windy sites dry out foliage and soil rapidly. A sheltered position with good air circulation but protection from prevailing winds suits coral bells perfectly.

Soil Preparation and Requirements

Coral bells demand well-drained soil above all else. They will not tolerate waterlogging, especially in winter. Heavy clay soils need amendment with plenty of organic matter – compost, leaf mould, or well-rotted manure. Sandy soils benefit from organic matter to improve moisture retention. Aim for a soil pH between 6.0 and 7.0, slightly acidic to neutral.

Before planting, dig the area thoroughly to at least 30cm depth. Incorporate a generous bucketful of organic matter per square metre. Add a handful of blood, fish and bone fertiliser per plant to provide slow-release nutrients. If your soil is very heavy, consider creating a raised bed or planting on a slight mound to improve drainage around the crown.

Step-by-Step Planting Guide

Water your coral bells plant UK pot thoroughly an hour before planting. Dig a hole twice the width of the root ball and the same depth. Gently tease out any circling roots. Position the plant so the crown (where stems meet roots) sits at soil level – not buried, not exposed. Backfill with your improved soil, firming gently around roots. Water well to settle soil and eliminate air pockets.

Apply a 5cm mulch of bark chips, compost, or leaf mould around the plant, keeping it clear of the crown. This conserves moisture, suppresses weeds, and protects roots from temperature extremes. Space plants 30-45cm apart depending on the mature size of your chosen variety. Closer spacing creates faster ground cover but may require earlier division.

Container Planting for Patios and Balconies

Coral bells excel in containers, making them perfect for UK patios, balconies, and small gardens. Choose a pot at least 30cm wide and deep with drainage holes. Use a quality peat-free multipurpose compost mixed with 20% perlite or grit for drainage. Add slow-release fertiliser granules at planting time.

Position containers where they receive morning sun or dappled shade. Water regularly – containers dry out much faster than ground soil. Feed with liquid seaweed or tomato feed every 2-3 weeks during the growing season. In winter, move pots to a sheltered spot against a house wall, raise on pot feet for drainage, and wrap with fleece during severe cold snaps.

Ongoing Care Through the Seasons

Spring Care: Awakening and Feeding

As temperatures rise in March, coral bells plant UK gardens push fresh growth from the crown. Remove any tattered or dead leaves from winter by cutting them at the base. Apply a balanced slow-release fertiliser around the base, or top-dress with compost. This feeds the spring flush and supports flower production. Watch for slugs and snails on tender new leaves – use organic pellets or barriers if needed.

Spring is also the ideal time to divide congested clumps (see division section below). New divisions establish quickly in spring moisture and warmth. If you notice the crown rising above soil level – a common issue as plants age – gently lift and replant deeper, or mound compost around the exposed crown.

Summer Care: Watering and Deadheading

Summer care focuses on moisture management. Coral bells have shallow root systems and suffer in drought. Water deeply once or twice a week during dry spells, more often for containers. Water at soil level, not over foliage, to prevent fungal issues. Mulch helps enormously with moisture retention.

Deadhead spent flower stems by cutting at the base once blooms fade. This redirects energy to foliage growth and prevents unwanted self-seeding (though seedlings rarely come true to type). In very hot spells, provide temporary shade for light-leaved varieties using shade cloth or by moving containers. Dark varieties may show some leaf scorch at edges – this is cosmetic and new growth will replace damaged leaves.

Autumn Care: Preparation for Winter

Autumn is the second planting window and a key maintenance period. Stop feeding by September to avoid soft growth vulnerable to frost. Remove any diseased leaves – Heuchera can suffer from rust or leaf spot in damp autumn weather. Do not compost diseased material.

Apply a fresh mulch layer after cutting back any spent flower stems. This protects roots from freeze-thaw cycles. If you have heavy clay soil, consider adding grit around plants to improve surface drainage over winter. Container plants should be moved to their winter positions by November.

Winter Care: Protection and Monitoring

Most coral bells plant UK varieties are fully hardy to -15°C or lower. However, winter wet kills more plants than winter cold. Ensure drainage is excellent. In very cold regions or exposed sites, a loose covering of fleece or straw over the crown provides extra insurance. Remove cover during mild spells to prevent fungal issues.

Check plants periodically for heaving – where freeze-thaw cycles push the crown out of the soil. If this happens, gently firm back in or cover with compost. Evergreen foliage may look tatty by late winter – this is normal. Resist the urge to tidy until spring when new growth shows where to cut.

Propagation: Multiplying Your Collection

Division: The Most Reliable Method

Division is the easiest and most reliable way to propagate coral bells plant UK gardeners love. It rejuvenates old plants and gives you free new ones. Divide every 3-4 years in spring or autumn when the centre becomes woody and flowering declines. Water the plant well the day before.

Dig up the entire clump with a fork, keeping as many roots as possible. Shake off excess soil to see the structure. The plant consists of multiple rosettes connected by woody rhizomes. Using a sharp knife or spade, cut between rosettes, ensuring each division has roots and several leaves. Discard the old woody centre. Replant divisions immediately at the same depth, water well, and mulch.

Spring divisions may flower the same year. Autumn divisions focus on root establishment and flower the following year. Both timings work well in UK conditions. Avoid dividing in summer heat or winter cold.

Growing from Seed: For the Patient Gardener

Growing coral bells from seed is rewarding but slow. Seed-grown plants vary from the parent – this is how new varieties arise. Collect seed from spent flower stems in late summer. Sow fresh on the surface of moist seed compost (light aids germination). Cover with a propagator lid or polythene bag. Keep at 18-21°C. Germination takes 2-8 weeks.

Prick out seedlings when large enough to handle. Grow on in individual pots. Plant out the following spring after hardening off. It takes 2-3 years for seed-grown plants to reach flowering size. For named varieties, division or buying plants is more reliable. But seed sowing is fascinating for plant enthusiasts.

Leaf Cuttings: A Specialist Technique

Leaf cuttings can produce new plants from a single leaf. This works best with large-leaved varieties. Take a healthy leaf with a short piece of petiole (leaf stalk) in spring or early summer. Dip the cut end in rooting hormone. Insert into a pot of 50:50 peat-free compost and perlite. Cover with a plastic bag. Place in bright, indirect light.

Roots and a tiny plantlet form at the base of the petiole in 6-8 weeks. Pot on once established. This method is slower than division but useful for increasing rare varieties. Success rates vary – expect 50-70% with good conditions.

Common Problems and Solutions

Vine Weevil: The Number One Enemy

Vine weevil is the most serious pest for coral bells plant UK growers. Adult beetles notch leaf edges at night from May to October. The real damage comes from larvae – white, C-shaped grubs that eat roots underground. Plants suddenly wilt and collapse, often in autumn or spring. By the time you notice, roots may be completely severed.

Check plants regularly by gently tugging – loose plants indicate root damage. Inspect roots of any wilting plant. Biological control with nematodes (Steinernema kraussei) applied in August-September targets larvae effectively. Encourage natural predators: birds, ground beetles, and centipedes. Avoid broad-spectrum insecticides that kill beneficial insects. For containers, use gritty compost and check roots when repotting.

Heuchera Rust: Managing Fungal Disease

Heuchera rust appears as orange-brown pustules on leaf undersides, with yellow spots on the upper surface. It thrives in humid, damp conditions – common in UK summers. Remove affected leaves immediately. Improve air circulation by spacing plants adequately. Water at soil level, not over foliage. Avoid high-nitrogen feeds that promote soft, susceptible growth.

Some varieties show better resistance. Villosa hybrids generally resist rust better than sanguinea types. If rust is persistent, consider preventive sprays with sulphur-based fungicide in spring. Always follow label instructions. Good hygiene – removing fallen leaves in autumn – reduces overwintering spores.

Crown Rot: Prevention Through Drainage

Crown rot kills more coral bells than any disease. It occurs when the crown sits in wet soil, especially over winter. Symptoms include blackening at the base, foul smell, and sudden collapse. There is no cure – prevention is everything. Ensure excellent drainage at planting. Never bury the crown. Mulch away from the crown, not over it.

In heavy soils, plant on a slight mound. Add grit to the planting hole. For containers, use pot feet and free-draining compost. If a plant shows early signs, you might save it by lifting, cutting away rotten tissue, dusting with sulphur powder, and replanting in fresh, gritty compost. But success is limited.

Slugs and Snails: Protecting New Growth

Spring growth is vulnerable to slug and snail damage. They love the tender new leaves. Use organic ferric phosphate pellets sparingly. Beer traps work well. Copper tape around pots deters them. Encourage hedgehogs, frogs, and birds. Go out at night with a torch and collect by hand. Nematodes (Phasmarhabditis hermaphrodita) applied to soil target slugs underground.

Mature, tougher leaves suffer less damage. The main risk period is April to June. Once leaves mature, damage becomes cosmetic. Some gardeners accept minor slug damage as part of a balanced ecosystem.

Sun Scorch and Heat Stress

Light-leaved varieties scorch in hot sun. Symptoms: brown, crispy leaf edges and bleached patches. Dark varieties tolerate more sun but can still scorch in extreme heat. Prevention: right plant, right place. Move containers to shade during heatwaves. For ground plants, provide temporary shade cloth. Water deeply in morning. Mulch heavily. Scorched leaves won’t recover but new growth will be fine.

Designing with Coral Bells in UK Gardens

Shade and Woodland Gardens

Coral bells plant UK woodland schemes are a classic combination. Their natural habitat is North American woodland edges, so they feel at home beneath deciduous trees. Plant in drifts of 5-7 of the same variety for impact. Mix varieties with contrasting foliage colours – dark purple next to lime green, silver next to caramel.

Underplant with spring bulbs: snowdrops, wood anemones, bluebells. The Heuchera foliage emerges as bulbs finish, hiding dying bulb leaves. Add ferns (Dryopteris, Athyrium), hostas, Tiarella, Brunnera, and hardy geraniums for a layered woodland tapestry. The different leaf shapes and textures create interest even when nothing is flowering.

Container Displays for Year-Round Interest

Few container plants offer 12 months of foliage colour like coral bells. Create a winter container with ‘Obsidian’, ‘Lime Rickey’, and ‘Caramel’ for a three-colour display. Add winter-flowering pansies, dwarf conifers, or ornamental grasses. In spring, tuck in tulip or daffodil bulbs between the Heuchera. Summer brings trailing lobelia or bacopa. Autumn adds ornamental kale or chrysanthemums.

Use a large container (40cm+ diameter) for a mixed Heuchera display. Ensure excellent drainage. Feed and water regularly. The foliage mound stays attractive even when seasonal additions come and go. Refresh the display annually by replacing seasonal plants and top-dressing with fresh compost.

Border Edging and Ground Cover

Coral bells make superb border edging. Their neat mounding habit defines edges without flopping onto paths. Plant 30cm apart in a single row along a border front. Choose one variety for a uniform look, or alternate two contrasting colours for rhythm. They suppress weeds effectively once established.

For ground cover on a bank or difficult slope, plant in a quincunx pattern (like the 5 on a dice) at 35cm spacing. This covers ground faster than rows. Mix with other shade-tolerant ground covers like Pachysandra, Vinca minor, or Epimedium for diversity. The evergreen foliage prevents soil erosion year-round.

Modern and Contemporary Schemes

In modern garden design, coral bells plant UK landscapers favour silver and dark varieties for their architectural foliage. Plant in geometric blocks or repeating patterns. Pair with black mondo grass (Ophiopogon planiscapus ‘Nigrescens’), silver grasses (Stipa tenuissima), or structural plants like Phormium. Use Corten steel or slate containers for a cohesive hard-landscaping palette.

Lighting transforms these plants at night. Uplight dark varieties to highlight leaf texture. Downlight silver varieties for a moonlit effect. The evergreen presence means the lighting scheme works year-round, not just in summer.

Buying Coral Bells in the UK

Where to Buy Quality Plants

UK gardeners have excellent sources for coral bells. Specialist nurseries offer the widest range and best advice. Look for Heuchera specialists like Heucheraholics, Plantagogo, or local nurseries with National Collections. RHS Plant Finder lists hundreds of suppliers. Garden centres stock popular varieties in spring – convenient but limited range.

Online mail-order nurseries deliver bare-root or potted plants. Bare-root plants (available autumn to spring) are cheaper and establish well if planted promptly. Potted plants can be bought year-round but cost more. Check reviews before ordering. Avoid cheap multi-packs from non-specialist sellers – these are often small, poorly rooted, or mislabelled.

What to Look for When Buying

Choose plants with multiple crowns (growth points) – these establish faster. Avoid plants with roots circling the pot bottom (pot-bound). Check for pests: vine weevil notches on leaves, aphids on new growth. Foliage should be clean, not yellowed or spotted. The crown should be firm, not mushy.

For named varieties, buy from reputable sources to ensure correct labelling. Mislabelled plants are common in the trade. RHS AGM varieties are a safe bet for performance. If buying in autumn, check the plant isn’t just a spring-potted plant that hasn’t rooted into the new compost.

Understanding Plant Sizes and Prices

Coral bells are sold in various sizes. 9cm pots (P9) are young plants – cheapest but take 1-2 years to reach full size. 2-litre pots are standard retail size – good balance of price and impact. 3-5 litre pots are specimen plants for instant effect. Bare-root divisions are sold by specialist nurseries in autumn/spring – excellent value.

Expect to pay £4-8 for a 9cm pot, £8-15 for 2-litre, £15-30 for larger specimens. Rare or new introductions cost more. Buying in autumn often yields better prices as nurseries clear stock. Spring offers the widest selection but highest prices.

Frequently Asked Questions About Coral Bells

Are coral bells evergreen in the UK?

Yes, most coral bells plant UK varieties are evergreen or semi-evergreen. They retain foliage through winter, though leaves may look tatty by February. New growth replaces old leaves in spring. In very cold winters or exposed sites, some leaf loss may occur but plants recover.

Do coral bells flower every year?

Yes, mature plants flower annually in late spring to early summer. Flowering may be reduced in very deep shade or if the plant is congested and needs division. Deadheading spent stems encourages a lighter second flush in some varieties.

Can coral bells grow in full sun in the UK?

Dark-leaved varieties tolerate full sun in cooler UK regions if soil stays moist. Light-leaved varieties scorch in full sun. In hot southern UK gardens, even dark varieties appreciate afternoon shade. Always ensure consistent moisture in sunny positions.

How long do coral bells live?

Individual plants live 5-10 years but become woody and less vigorous after 3-4 years. Regular division effectively makes them immortal – each division is a genetic clone of the original. Many gardeners have maintained the same variety for decades through division.

Are coral bells poisonous to pets?

Heuchera is generally considered non-toxic to dogs and cats. However, eating large quantities may cause mild stomach upset. The plant is not listed as toxic by major veterinary poison control centres. As with any plant, discourage pets from chewing garden plants.

Why is my coral bells plant dying in the middle?

This is natural ageing. The centre becomes woody and stops producing leaves. The plant grows outward as a ring. This signals it’s time to divide. Dig up in spring or autumn, discard the woody centre, and replant the healthy outer rosettes.

Conclusion: Embracing Coral Bells in Your Garden

Few plants offer as much reward for so little effort as coral bells plant UK gardeners have embraced. Their staggering variety of foliage colours, year-round presence, and adaptability to our climate make them indispensable. Whether you have a sprawling woodland garden, a tiny urban courtyard, or a few pots on a balcony, there is a Heuchera that will thrive and delight.

Start with a few reliable AGM varieties suited to your conditions. Observe how they perform through the seasons. Experiment with combinations. Share divisions with friends. Before long, you will understand why these North American natives have become such beloved residents of British gardens. Their leaves paint the garden in colours no flower can match, and they do it when we need it most – through the long, grey months when colour is precious.

The coral bells plant UK story is still being written. Breeders continue developing new colours, patterns, and forms. Each spring brings fresh introductions to trial. But the core appeal remains unchanged: beautiful foliage, easy care, and reliable performance. Plant some this autumn. Your garden will thank you every day of the year.

Frequently Asked Questions

Are coral bells hardy in UK winters?

Yes, most coral bells varieties are fully hardy throughout the UK, tolerating temperatures down to -15°C or lower. The main winter threat is waterlogging rather than cold, so ensure excellent drainage.

Do coral bells spread aggressively?

No, coral bells are clump-forming perennials that spread slowly. They do not run or become invasive. The clump gradually expands over years but stays neat and contained.

Should I cut back coral bells in autumn?

No, do not cut back coral bells in autumn. The evergreen foliage protects the crown through winter. Remove only diseased or damaged leaves. Tidy up tattered foliage in spring when new growth appears.

Why are my coral bells leaves turning brown and crispy?

Brown crispy edges usually indicate sun scorch (too much direct sun for the variety) or drought stress. Move light-leaved varieties to more shade and ensure consistent moisture, especially for container plants.

Can I grow coral bells from seed collected from my plants?

Yes, but seedlings will not come true to the parent variety. They will be variable. For named varieties, propagation by division is the only way to maintain the exact characteristics.

What compost is best for coral bells in pots?

Use a quality peat-free multipurpose compost mixed with 20% perlite or horticultural grit for drainage. Add slow-release fertiliser at planting. Avoid water-retentive gels which can cause crown rot.