Plants, weeds or moss growing in your gutter? What it means and what to do

How it gets that far

A gutter collects more than leaves. Moss washed off the roof, grit, seeds, dust and bird droppings all settle in the bottom, and in time they form a dark, soil-like sludge. Once it's deep enough to hold water, seeds blown in by the wind or dropped by birds start to grow.

You're far from alone. On a Mumsnet thread about gutters, one homeowner had "weeds growing in ours", and another found "a thistle that had been growing in the gutter".

What's growing, and how much it matters

Why plants in a gutter are a problem

• They block the flow. Roots and sludge hold back water, so the gutter fills and overflows in heavy rain. Cadw, the Welsh Government's historic environment service, warns that overflowing gutters "can lead to damp walls and decay".
• They add weight. Wet sludge and plants are heavy. One Mumsnet user's cousin had gutters that "collapsed the other week with all the weight of the crap in it."
• Roots get into joints. A root that works its way into a joint can open it up, and then it leaks even after the plant is gone.
• They point to other problems. The Department for Communities in Northern Ireland notes that vegetation growth on a building is one of the signs of a fault in the rainwater system.

Buddleia: take it out early

Buddleia is the plant most people notice, because it grows into a proper shrub in the oddest places, including gutters and walls. The property specialist Environet says buddleia "can grow practically anywhere" and "doesn't need much in the way of soil to start growing". It warns that the roots "grow into areas like walls, guttering, and foundations and may eventually cause structural damage", and that in walls or guttering "speedy removal is a good idea".

Pull a seedling while it's small. Once it's woody, the roots need taking out with it, or it simply grows back.

What to do about it

• If the gutter is low and safe to reach, pull out the plants, roots and all, and scoop out the sludge underneath. Then pour water through to check it reaches the downpipe.
• If it's two storeys up or over a conservatory, leave it. Pulling at a plant from a stretched-out ladder is exactly how people fall.
• Check the wall below for green streaks or stains, which show the gutter has been overflowing for a while.
• Check the downpipe. If the gutter has been full for years, the bend at the top of the pipe is probably packed too.
• If birds are using the plants or the gutter to nest between March and September, wait until they've finished. Active nests are protected by law.

Stopping it happening again

A yearly clear, timed after the leaves have fallen, stops the sludge ever getting deep enough for roots. If moss from the roof is the main source, removing the heavy moss from the slopes above helps too. Gutter guards can help with leaves, but moss and seeds can still get underneath, where you can't see them. Our gutter guard guide goes into that.

How we clear overgrown gutters

We clear gutters by hand, roots and all, and scrape out the sludge underneath rather than just pulling the tops off the plants. We test every downpipe, check the joints the roots have been in, and send you before and after photos of each run. If a joint has opened up or a bracket has given way under the weight, we'll show you and quote to fix it.

Written by Hawkes Roofing, roofers based in St Albans who clear gutters by hand across Hertfordshire, Buckinghamshire and north-west London. Last reviewed 26 October 2026.