What Is in Your Gutter? Moss, Silt, Granules and Seeds
When a gutter is cleared, what comes out tells a story about the roof and garden above it. Some debris is seasonal, some builds up over years, and some is a sign that the roof itself needs attention.
Moss
Clumps of moss are the most common thing in gutters below mossy roofs. Moss dries and lets go of the tiles in dry weather, then rolls down the slope. Thick lumps can block outlets on their own. A gutter full of moss is often the first sign that the roof needs cleaning.
Silt and black sludge
Over time, dust, decayed leaves and fine roof grit settle into a dark, mud-like layer. It holds water, gets heavier and can set firm when it dries. Silt is what makes gutters sag and what plants root into.
Tile granules and grit
Concrete tiles shed sand-like grit as their surface wears, and felt-type roofs shed mineral granules. A lot of grit can suggest tiles are weathering. It settles in the bottom of the gutter and at outlets.
Leaves, needles and seeds
Leaves arrive in autumn, conifer needles all year, and seeds and catkins in spring. Seeds in silt often germinate, which is why small plants and even saplings can grow in gutters. See plants in gutters.
Nesting material and other finds
Twigs, feathers and moss from nests, balls, shuttlecocks and the occasional toy are all regular finds. Nesting birds are protected while active, so work around an active nest must wait.
What it tells you
Mostly moss means the roof needs attention. Mostly leaves means trees are the main source and more frequent cleaning may help. Lots of grit can point to tile wear. Plants mean the gutter has been holding silt and water for some time.
Seasonal patterns
Spring often brings seeds, blossom and catkins. Summer is usually the quietest time, though roof moss can dry and roll off in hot spells. Autumn brings the heaviest leaf fall. Winter brings storm debris, twigs and moss loosened by frost. Knowing when your gutters fill helps choose when to clear them.
Weight of a full gutter
Wet silt and moss are heavy. A gutter carrying years of debris and standing water is under far more load than it was designed for, which strains brackets and joints and leads to sagging.
Debris and downpipes
What sits in the gutter eventually washes towards the outlet. Moss lumps and silt are the main causes of blocked downpipes. Clearing the gutter regularly is the simplest way to keep downpipes running. See clogged downpipes.
Insects and smells
Wet debris left for a long time can smell and attract insects. Gnats and other small flies breed in standing water. A gutter that holds water after rain may also attract mosquitoes in summer. Clearing and correcting the fall removes the standing water.
Asbestos-era materials
On some older properties, concrete or fibre-cement gutters and roofing were used. If you suspect your gutters or roof contain asbestos, have them tested before any work that could disturb them. See concrete gutters.
Finding valuables
Lost items do turn up in gutters, from keys and toys to balls kicked onto the roof. If you have lost something you suspect is up there, mention it when you book.
Moss balls and outlets
Dried moss from roofs forms rounded balls that roll along the gutter in wind and rain until they reach an outlet. One or two can be enough to block a downpipe. That is why gutters below mossy roofs often block suddenly, even when they looked clear a few months earlier.
Debris and damp
A gutter packed with silt holds water against the fascia, which can rot timber boards over time. Keeping gutters clear protects the fascia as well as the walls.
Book a gutter clear
Our gutter cleaning removes all of it, clears the outlets and tests the flow. Quotes are free across Hampshire, Surrey and Sussex.
Get a free quote
Send a few details and ground-level photos if you have them. We will reply with honest advice and a free, no-obligation quote.
Frequently asked questions
What is the black sludge in my gutter?
Silt made from dust, decayed leaves and roof grit. It holds water and adds weight.
Why is there sand in my gutter?
Concrete tiles shed grit as their surface wears.
Why are plants growing in my gutter?
Seeds have rooted in silt that has been holding water.
Does moss in the gutter mean my roof needs cleaning?
Often yes. It is usually moss coming off the tiles.
Do you take the debris away?
Ask when booking and we will explain what happens to the debris for your job.
Is gutter debris good for the garden?
Leaf and moss debris can be composted, but debris from treated roofs is better disposed of. Ask us about yours.
How much debris is normal?
It depends on trees and roof type. A thin layer is normal; gutters half full need clearing.
Can grit in gutters mean my roof is failing?
Some grit is normal on concrete tiles. Large amounts suggest weathering worth checking.
Pristine Roof Cleaning Solutions is based in Petersfield, covers Hampshire · Surrey · Sussex and is fully insured to £5,000,000 public liability.
Related guides
- Moss Falling Into Gutters and Blocking Them
Moss falling from the roof into gutters causes blockages and overflow. Why it happens, why clearing alone doesn't last, and how to deal with the source.
- Plants Growing in Your Gutters
Grass, weeds or seedlings growing in gutters mean silt has built up. Why it happens, the damage roots can do, and how gutters are cleared and checked.
- Leaves in Gutters From Nearby Trees
Nearby trees fill gutters with leaves, needles and seeds. Which trees cause most trouble, when to clear, and how to plan gutter care under trees.
- How Often Should You Clean Your Gutters?
How often to clean gutters depends on trees, roof type and past problems. Learn the signs, seasonal timing and when once a year is not enough.
Last updated 2026-11-03.