How to Kill Bracken

You’ve cut it back. You’ve pulled it out. You’ve even tried burning it. And yet every spring, the bracken returns – taller and thicker than before.

This isn’t bad luck. It’s biology. Bracken (Pteridium aquilinum) is one of the oldest and most common weeds in the UK, and it’s spent millions of years perfecting the art of survival. The fronds you see above ground are just the tip of the iceberg. Below the surface lies a network of rhizomes that can extend a metre deep and spread several metres in every direction.

That’s why cutting alone will never work. You’re essentially giving it a haircut while leaving the entire plant intact underground.

But bracken can be killed permanently – you just need to understand how it works and attack it properly.

How to Identify Bracken

Bracken is hard to miss once established. Look for these features:

The fronds are large and triangular, divided into three main sections, each with smaller leaflets arranged in a herringbone pattern. In spring, new shoots emerge as distinctive curled “fiddleheads” that unfurl as they grow. Mature plants typically reach 1-1.5 metres tall, sometimes exceeding 2 metres in ideal conditions.

Unlike most garden ferns that form neat clumps, bracken spreads aggressively via underground rhizomes. If you’re seeing bracken pop up across a wide area rather than in a contained spot, those individual plants are likely all connected beneath the soil.

Bracken thrives in acidic soils and partial shade, though it tolerates full sun. It’s particularly common along woodland edges, on heathland, and in gardens that border open countryside.

Why Bracken Is So Hard to Kill

Bracken’s survival strategy is devastatingly effective. The underground rhizome system stores enormous energy reserves – enough to keep regenerating new fronds even after repeated cutting. Studies show that a single bracken plant can have rhizomes extending 5 metres or more, with the deepest reaching over a metre down.

This deep root system puts bracken in the same league as other notoriously difficult weeds like horsetail, creeping thistle, and Japanese knotweed – all require a systemic approach rather than just removing what’s visible.

When you cut the fronds, you remove the plant’s ability to photosynthesise temporarily. But those deep rhizomes simply draw on stored energy to send up new growth. Worse, cutting can actually stimulate the plant to produce more shoots as a survival response.

This is why permanent weed control requires getting the active ingredient down to those roots.

How to Kill Bracken

There are two approaches: the long game (cutting) or the direct approach (herbicide). For most gardeners dealing with established bracken, herbicide is the practical choice.

The Cutting Method (2-5 Years)

If you’re committed to chemical-free control, repeated cutting can eventually exhaust bracken’s energy reserves. Cut the fronds at ground level when they’re fully unfurled in early summer – typically June or July. Repeat whenever regrowth reaches full size.

The key is consistency. Miss a season and you’ve undone months of work. Expect this process to take 3-5 years of persistent cutting before the rhizomes are fully depleted.

The Herbicide Method (1-2 Seasons)

A systemic glyphosate-based weedkiller offers faster results. Glyphosate is absorbed through the leaves and transported throughout the plant – including down to those deep rhizomes.

Timing is critical. Spray when the fronds are fully expanded but still green and actively growing – typically late July to early September. At this stage, the plant is moving nutrients from the fronds down to the rhizomes for winter storage. Your herbicide hitches a ride on this natural process.

Apply on a dry day when rain isn’t forecast for at least 6 hours. Ensure good coverage of all fronds. The bracken will yellow and die back over the following weeks.

Expect some regrowth the following season from rhizome sections that didn’t receive a lethal dose. A follow-up treatment in year two usually finishes the job. For particularly stubborn infestations, you may need the strongest weedkiller formulation available. For long-lasting weed control in areas where bracken keeps returning, residual herbicides can prevent regrowth for months.

What About Asulox?

You may have read that Asulox (asulam) is the best bracken killer. It was – but it’s no longer available for garden use in the UK. Glyphosate-based products are now the most effective option for home gardeners.

Preventing Bracken From Returning

Once you’ve cleared bracken, keeping it away requires vigilance:

Monitor the area each spring for any new fiddleheads emerging. Treat or remove these immediately before they can re-establish. If your garden borders countryside or woodland where bracken grows, consider installing a root barrier along the boundary.

Establishing competitive planting helps too. Dense groundcover or vigorous shrubs can shade out any bracken seedlings and make the area less hospitable for regrowth.

Bracken spreads by both rhizomes and windborne spores, so complete prevention isn’t always possible if there’s bracken nearby. But catching new growth early – when it’s just a few small fronds – is far easier than battling an established colony.

Bracken often shares territory with other tough weeds. If you’re also dealing with brambles or woody growth in the same area, tackle them at the same time for best results.

Frequently Asked Questions

How long does it take to kill bracken?

With herbicide treatment, expect visible die-back within 2-4 weeks. However, complete eradication typically takes 1-2 seasons, as some rhizomes may survive the initial treatment and produce regrowth the following year. The cutting method takes 3-5 years of consistent effort.

What is the best time of year to spray bracken?

Late July to early September, when fronds are fully expanded and the plant is actively transporting nutrients down to the rhizomes. Spraying too early (when fronds are still unfurling) or too late (when they’re yellowing) reduces effectiveness.

Will cutting bracken kill it?

Eventually, yes – but it takes years. Cutting removes the plant’s ability to photosynthesise, forcing it to draw on stored energy in the rhizomes. Repeated cutting over 3-5 years can exhaust these reserves. However, inconsistent cutting may actually stimulate more vigorous growth.

Does bracken come back after treatment?

Often, yes – at least partially. Bracken’s extensive rhizome network means some sections may survive the first herbicide application. A follow-up treatment in the second year typically eliminates remaining plants. After that, any new growth is usually from spores rather than the original plant.

Is bracken harmful to dogs?

Bracken contains compounds that are toxic if eaten in large quantities over time. However, dogs rarely eat bracken, so the risk is low in practice. A bigger concern is that dense bracken provides ideal habitat for ticks, which can carry Lyme disease. Check your dog after walks through bracken-heavy areas.

The Bottom Line

Bracken is tough, but it’s not invincible. The key is targeting the underground rhizome network rather than just the visible fronds. A systemic weedkiller applied at the right time will travel down to the roots and kill the entire plant – something cutting and pulling can never achieve.

Ready to reclaim your garden from bracken? Our Strong Weed Killer reaches the deep rhizome network that cutting and DIY methods can’t touch – giving you permanent control, not temporary setbacks.