What happens if you put Coffee grounds in the wrong bin?

Never tip a thick layer of grounds on soil or in a bin; it mats and stops air and water.

Where do Coffee grounds go?

Compost heap or food waste. Good material in both, in moderation.

Food waste collection

Used grounds are a nitrogen-rich green material for a compost heap, and roughly neutral in pH once brewed rather than acidic as the folklore has it. They compact into an airless mat if piled thickly, so mix them through the heap rather than layering them. Worm bins take them in small amounts. Coffee shops give away sacks of grounds free, which is worth knowing if you are building a heap. Food waste collections take them wherever they exist, so check whether your area has one.

How to prepare it

Mix through the heap with brown material rather than layering thickly.
Paper filters compost with the grounds.

What not to do

Never tip a thick layer of grounds on soil or in a bin; it mats and stops air and water.

Kerbside collection rules genuinely vary by council and county, and local rules always win over general guidance. The reasoning above is what transfers — if your service differs, it will usually be for a reason described here.

Other things that go to food waste collection

Food scraps and leftovers Food waste collection where you have one — it accepts cooked food, meat and dairy, unlike a home compost heap.
Teabags Food waste or compost — but many bags are sealed with polypropylene, and that plastic mesh stays behind.
Cooking fat, lard and dripping Let it solidify, scrape it into the food waste or general bin. Never down the drain, at any temperature.
Bones Food waste collection if you have one. Never a home compost heap.
Eggshells Compost or food waste. Crush them first or they will still be recognisable next year.

Common questions

Where do Coffee grounds go?: Compost heap or food waste. Good material in both, in moderation.
What happens if you put Coffee grounds in the wrong bin?: Never tip a thick layer of grounds on soil or in a bin; it mats and stops air and water.

Where do Food scraps and leftovers go? Food waste collection where you have one — it accepts cooked food, meat and dairy, unlike a home compost heap.
Where do Teabags go? Food waste or compost — but many bags are sealed with polypropylene, and that plastic mesh stays behind.
Where do Cooking fat, lard and dripping go? Let it solidify, scrape it into the food waste or general bin. Never down the drain, at any temperature.
Where do Bones go? Food waste collection if you have one. Never a home compost heap.
Where do Eggshells go? Compost or food waste. Crush them first or they will still be recognisable next year.
Where do Household batteries (AA, AAA, C, D, 9V) go? Shop or manufacturer take-back
Where do Lithium-ion batteries go? Shop or manufacturer take-back
Where do Vapes and disposable e-cigarettes go? Shop or manufacturer take-back
Where do Medicines and tablets go? Pharmacy
Where do Pizza boxes go? Kerbside recycling bin
Where do Leftover wet paint go? Household waste recycling centre

Sources

US Environmental Protection Agency — EPA (Public domain (US Government))

How these figures are compiled and checked