For lots of us, the day doesn’t really start until the kettle’s boiled and the first coffee is in hand. That quiet moment over a mug feels like a daily ritual – a reset before everything else begins. But once the cup is emptied, the story usually ends with a soggy puck of grounds going straight in the bin.

In this blog, we’re giving those grounds a second act. Used carefully, they can become a small but mighty part of a more sustainable, soil-friendly garden routine – turning something that would have been waste into a quiet boost for the life beneath your wellies.

This isn’t about miracle cures or gardening myths. Just simple, science-backed ways to let your morning brew work twice.

What’s actually in coffee grounds?

Used coffee grounds are mostly organic matter – tiny fragments of seed that microbes love to break down.

They contain:

• Nitrogen (around 1–2%), plus smaller amounts of phosphorus, potassium and micronutrients like magnesium and calcium.
• A near-neutral pH (often around 6.5–6.8), which means they don’t significantly acidify soil, despite what you often hear.

On their own, they’re not a complete fertiliser and they don’t magically fix poor soil overnight. What they do offer is:

• Extra organic matter to improve structure over time
• Food for soil microbes
• A way to keep a common waste product out of landfill

The key is how you use them.

Myths, gently debunked

Before we get into the practical ideas, it’s worth clearing up a few common claims around coffee grounds.

“They make the soil nice and acidic.”

Brewed coffee is acidic; spent grounds are not particularly. Once water has run through, most of the acidity is in your mug, not in the leftover grounds. Tests find used grounds sitting close to neutral, so they’re not a reliable way to acidify soil for blueberries or hydrangeas.

If you need to change soil pH, you’re better off using dedicated soil amendments and a soil test.

“You can just throw them straight on the bed.”

You can sprinkle small amounts around established plants, but piling on thick layers of grounds is risky. Fresh grounds still contain caffeine and other compounds that can slow germination and root growth if used in bulk, especially around seedlings.

Used in moderation and ideally composted first, they’re much safer and more useful.

“They’re brilliant for pest control.”

There is some evidence that strong liquid coffee can help with slugs and snails, but the amount of caffeine left in used grounds on their own is low and the results are mixed.

Think of coffee grounds primarily as organic matter and compost food, not as a miracle slug shield.

The best way to use coffee grounds: in the compost

If you remember just one thing from this blog, let it be this:

The safest, most effective way to use coffee grounds is to compost them.

Why compost first?

When coffee grounds go into a compost heap:

• Microbes break down the organic matter and any leftover caffeine
• The nutrients become part of a balanced, crumbly compost
• Potential negative effects on seedlings and roots are greatly reduced

How to add them:

1. Collect your grounds.

Keep a small caddy or tub by the coffee machine. Add only used grounds (no pods or paper filters coated in plastic).

2. Treat them as “greens.”

Coffee grounds are nitrogen-rich, so they count as a “green” in composting. Balance them with plenty of “browns” – dry leaves, straw, torn cardboard or paper.

3. Aim for moderation.

As a rough guide, try not to let coffee grounds become more than 20–25% of your compost mix by volume. Too much of any one ingredient can slow the heap down.

4. Mix, don’t layer.

Sprinkle grounds through the heap rather than tipping them in as a thick mat, which can become compacted and slimy.

Over time, those daily handfuls will turn into rich compost you can use on beds, borders and containers – a quiet win from something that would otherwise be thrown away.

Light touch: using coffee grounds directly in the garden

If you’d like to use some grounds more immediately, you can – with a gentle hand.

1. A sprinkling in the soil

For established plants (not seedlings), you can:

• Let the grounds dry out a little so they’re easier to handle
• Sprinkle a very thin layer over the soil around the plant – think “dusting of cocoa powder” rather than icing sugar avalanche
• Lightly fork or scratch them into the top few centimetres of soil

This adds organic matter and feeds the soil life without smothering the surface or overwhelming young roots.

Avoid:

• Around newly sown seeds or tiny seedlings
• In pots already struggling with drainage or compaction
• In beds filled with Mediterranean herbs or very drought-tolerant plants, which prefer leaner, freer-draining soils

2. In a mixed mulch

Pure coffee grounds don’t make a good mulch on their own – they can form a crust that repels water. Mixed with other materials, they’re much better.

Try blending small amounts of grounds into:

• Leaf mould
• Well-rotted compost
• Fine bark or woodchip

You can also mix these in with a a peat-free soil improver that will add nutrients and organic matter to your soil, such as – Caledonian Green Goodness.

Then use this mix as a top-up mulch, around shrubs and perennials over winter, keeping a little distance from stems. This helps protect the soil surface and slowly feeds the life underneath.

A word on pets and wildlife

If you have dogs that like to “help” in the garden, be cautious. Coffee grounds still contain caffeine, which can be toxic if eaten in larger amounts.

To be safe:

• Keep fresh grounds in a closed container
• Use them in lidded compost bins or mixed well into heaps, rather than scattered where curious noses can reach them

As with all amendments, a little care now keeps everyone – human, plant and animal – happier in the long run.

Small habit, big picture

On their own, coffee grounds aren’t going to transform a garden overnight. But as part of a wider shift towards circular, low-waste gardening, they’re a lovely example of how small habits add up.

• You’re diverting a regular waste stream from the bin
• You’re feeding soil life instead of relying solely on bagged fertiliser
• You’re paying attention to what’s going into the garden, not just what you’re taking out

Next time you tip out the cafetière, you might pause for a second and see those grounds differently – not just leftovers from your morning, but the beginnings of future soil.

From bin to bloom, one cup at a time. ☕🌱