← All guides · Reduction & renovation · Updated September 2026

How to fill gaps in a hedge: gapping up, step by step, for Broadstairs CT10.

A bare patch in an established hedge is one of the most common hedge problems in autumn. An old privet has died back in one section. A frost-hit Griselinia has opened up a gap. A yew has a hollow in the middle that no amount of trimming will fill. Here is the step-by-step process for gapping up an existing hedge correctly on the Thanet chalk, so the new plants knit in and the repair holds.

Steps

Step 1: Diagnose why the gap appeared before you plant anything

Planting into an undiagnosed gap is the single most common mistake. If the original plants died, the cause is almost certainly still present, and the new plants will fail the same way. The main causes on the Thanet coast:

• Drought stress on Margate chalk. The thin free-draining chalk across the coastal strip holds little moisture in a dry summer. Plants that were never watered adequately in their first two years slowly thin out, and a dry spring finishes them. Fix the watering regime before replanting.
• Root competition from an established hedge. Privet and laurel hedge roots spread aggressively. New plants in the gap will compete with mature hedge roots for water and nutrients on chalk that has very little of either. Heavy soil improvement is non-negotiable.
• Salt-scorch die-back on front-line species. A bad easterly in January kills the outer foliage on exposed Griselinia or Escallonia; a gap that looks structural is often recoverable if you leave it until June and check whether inner wood still responds. Cut a small nick in the stem: green cambium means the plant is alive and will regrow.
• Over-cutting into dead wood on conifers. Leylandii and Cupressus cut back past the live green zone will not regenerate. That section of a conifer hedge is permanently dead and must be replanted with a different species, because replanting Leylandii into a Leylandii gap gives you the same hedge problem in 15 years.
• Box blight or box tree moth. A hollow in a box hedge is almost always disease or pest related. Treat the cause before gapping up, or the new box plants will be infected within a season.

Step 2: Clear dead material cleanly from the gap

Remove dead stems to ground level. Cut stubs flush or slightly below. For privet and laurel, the stump will often re-shoot: if the root system is healthy, those re-shoots are faster than a new plant. Give it one growing season to respond before assuming the root is dead. For Leylandii and cypress, remove the stump and as much root as practical, since decaying conifer roots harbour honey fungus (Armillaria) which will kill new broadleaved plants.

Step 3: Improve the soil in the gap thoroughly

Dig out the planting strip to two spade depths (roughly 50cm). On the chalk geology across CT10, you will often hit solid chalk at 30-40cm: that is normal. Break it up with a fork where you can; you cannot remove it, but you can fracture it so roots can penetrate. Back-fill with a 50/50 mix of the excavated soil and well-rotted compost or leaf mould. No peat. Add a generous handful of slow-release general fertiliser per metre of gap. Chalk is naturally alkaline, which suits most hedging species, but the key deficit on Thanet chalk is moisture retention and organic matter, not pH.

Step 4: Choose the replacement species

For gaps in an existing formal hedge, like-for-like is usually right: same species, same variety. The new plants will eventually match the established hedge's colour, texture and growth rate. The exceptions:

• Leylandii and cypress gaps: replant with yew, hornbeam or beech instead. Yew is the best long-term choice and takes the coast well once established.
• Box gaps caused by blight: replant with Ilex crenata (Japanese holly), which is visually almost identical to box but blight-immune.
• Gaps in mixed native hedges (hawthorn, blackthorn, dog rose): use the same native mix, ideally from a UK-grown bare-root supplier. Avoid container-grown substitutes that are likely to be non-native provenance.
• Salt-wind front-line gaps (clifftop, North Foreland): replace failed species with the coastal-tolerant tier: Escallonia, Olearia, Euonymus fortunei. If the original species failed due to salt exposure, don't replant it in the same spot.

Step 5: Plant at the correct spacing for your species

Bare-root plants: 2-3 per metre for most formal hedging species (privet, beech, hornbeam, hawthorn). 1-2 per metre for larger species (laurel, Portuguese laurel, Griselinia). Container-grown plants at the same centres, but match pot size to the existing hedge height: a 2-litre pot in a gap in a 2m privet hedge will take 5 years to fill in; a 10-litre container will reach cutting height in 2-3 seasons. Stagger the plants in a slight zig-zag if the gap is wide enough (over 45cm) for faster knitting.

Step 6: Plant correctly, stake if needed, protect from rabbits

Dig a hole wide enough for the root system to spread without bending. Bare-root: spread the roots, backfill to the soil mark on the stem, firm in with your heel. Container: plant at exactly pot depth, no deeper. Tall bare-root specimens (over 60cm) need a low stake and tie on chalky free-draining soil, where wind-rock is the main establishment killer. In any garden backing onto open land, fit a spiral rabbit guard on every new plant.

Step 7: Water in and mulch immediately

Water every new plant thoroughly at planting: at least 10 litres per plant on chalk, not a token splash from a can. Apply a 75mm bark mulch disc around each plant, keeping it clear of the stem. The mulch is important on Thanet chalk: it reduces surface moisture loss and suppresses competing grass and weed roots during the critical first summer. Replace it if it breaks down in year two.

Step 8: Set the watering schedule for the first summer

East Kent is one of the drier parts of England, with around 615mm of rain a year at Manston. New plants in a chalk gap need a minimum of 10 litres per plant per week in any week without meaningful rain, from April through September of the first year. For bare-root plants put in during November-February, start the watering regime the following April as growth begins. Missing two consecutive weeks in a dry June or July on chalk is enough to lose a new plant.

When to do gapping up: timing on the Thanet coast

Bare-root plants are the cheaper and generally more successful option for most hedging species: order from a UK-grown bare-root nursery for delivery between November and March. Plant them as soon as they arrive; bare roots must not dry out. For a gap that needs filling during the growing season (April-October), use container-grown stock instead: the root ball stays intact and establishment is less weather-dependent, though the cost per plant is higher. The one timing constraint that applies year-round is the nesting-season check: even a planting job during the nesting window can involve moving or cutting adjacent hedge branches, which brings WCA 1981 into play.

Species recovery times on Margate chalk

Approximate times for a correctly planted gap to match the established hedge height, assuming the watering and mulching regime above is followed:

• Privet: 2-3 seasons from bare-root. Fast.
• Hawthorn, mixed native: 3-4 seasons from bare-root. Very vigorous once past year one.
• Beech, hornbeam: 3-5 seasons from bare-root. Slower at the start, but both hold well on chalk.
• Griselinia: 2-3 seasons from a 5-litre container. Salt-wind vigour is good once roots find the chalk fractures.
• Escallonia: 2-3 seasons from container. Often flowers in year two if the gap is south-facing.
• Yew: 5-7 seasons from a 3-litre bare-root. Slow but definitive. Worth the wait for a formal hedge that is expected to last decades.
• Ilex crenata (box replacement): 3-4 seasons from a 2-litre container to match an existing formal box hedge.
• Laurel (cherry or Portuguese): 2-3 seasons from a 10-litre container if the gap is large; faster from container than bare-root for large-leaved species.

What not to do

Three common mistakes in gaps, worth stating plainly:

• Planting the same species in a failed spot without fixing the cause. If the original plant died of salt-scorch at a front-line clifftop position, a replacement of the same species will fail at the same age.
• Planting container-grown stock too deep. The root-to-stem junction must sit at soil level, never buried. Burying the stem junction causes stem rot in the first wet autumn.
• Planting and not watering. On Thanet chalk, that is a reliable way to lose every plant in the gap. The mulch helps, but it does not replace water.

Sources: Hedgelink, "Restoration of a Hedge: Plant Up The Gaps" (YouTube, February 2025); Hedgelink "Close the Gap" hedgerow restoration project guidance; RHS, Hedges: Renovation Techniques; Wildlife and Countryside Act 1981, section 1; Met Office climate averages 1991-2020, Manston station.