If your potting mix smells musty, sour, or like rotten eggs when you water, something in the pot isn’t drying properly. Why indoor plant soil smells bad is almost always about trapped moisture, low airflow, or organic matter breaking down in oxygen-poor compost.

If you’re unsure whether you’re watering too often, you can also read Indoor Plant Watering Mistakes.

Quick answer: why indoor plant soil smells bad

• Musty smell: soil staying damp too long
• Sour smell: stale compost + stressed roots
• Rotten egg smell: waterlogged, oxygen-poor soil (urgent)
• Fast fix: empty the saucer + let the top 5–7cm dry; if it smells like rotten eggs, check roots and repot

Do this first: Empty the saucer, then check the soil 5–7 cm down. If it’s wet there, pause watering until it dries.

Why Indoor Plant Soil Smells Bad: What’s Happening in the Pot

Healthy potting mix smells earthy. Bad smells start when compost stays wet long enough that oxygen drops. In a pot, that happens quickly — especially in winter, low light, or if the pot is too big.

When soil is constantly damp:

• roots struggle to breathe

• helpful microbes decline

• “smelly” bacteria take over

• rot risk increases

The fix is usually simple: get the pot drying at a healthier rate and refresh the compost if it’s gone stale.

The 7 Most Common Causes (and the Fast Fix for Each)

1) Overwatering (the most common cause)

Too much water — or watering too often — is the biggest reason soil turns sour or musty.

Fast fix

• Don’t water again until the top few centimetres are dry

• Lift the pot to feel the weight (heavy = still wet)

If you want a cleaner routine, read Perfect Watering Schedule for Indoor Plants.

2) Standing water in a saucer or cachepot

A plant pot riser for drip trays lifts the pot slightly so it isn’t sitting in runoff water, helping the soil dry out properly and reducing bad smells.

Even if you water correctly, leaving water sitting underneath keeps the bottom layer constantly soaked.

Fast fix

• Empty saucers 10–15 minutes after watering

• If you use a decorative outer pot, never let water collect inside it

3) Poor drainage (no drainage holes or blocked holes)

If water can’t leave the pot, the soil turns stale and roots suffocate.

Fast fix

• Use pots with drainage holes

• Check holes aren’t blocked by compacted soil

• Repot if needed

You can also read Improve Indoor Plant Drainage.

4) Soil is too dense or broken down

Old compost can collapse into a heavy, muddy texture that holds water for ages.

Fast fix

• Scrape off and replace the top 2–3 cm (mild cases)

• Repot into a fresher, airier mix (persistent smell)

A free-draining indoor potting mix helps compost dry evenly and prevents stale smells returning.

5) Pot is too big for the plant

A small plant in a large pot means lots of wet compost with not enough roots to use the moisture. It stays wet… and starts to smell.

Fast fix

• Downsize one pot size (if roots are small)

• Or water only a ring around the root zone (temporary fix)

6) Low light / cold room slows drying

In winter or low light, plants drink less and soil dries far slower — even if you’re watering the same as summer.

Fast fix

• Move the plant to brighter, indirect light

• Reduce watering frequency

• Give the pot more airflow (don’t cram it among other pots)

If your plant shelf is crowded, spacing pots out slightly can genuinely reduce smell problems.

7) Root rot or anaerobic bacteria (the “rotten egg” smell)

If the smell is strong and unpleasant (especially rotten eggs), treat it as urgent. The soil has likely gone oxygen-poor and roots may be rotting.

Fast fix

• Slide the plant out and inspect roots

• Trim mushy roots and remove soggy compost

• Repot into fresh, free-draining mix

• Water lightly once, then let it dry slightly before watering again

If you suspect rot, read Root Rot Houseplants.

The Fast “Smell Fix” Checklist (Do This in 10 Minutes)

If you want the quickest improvement today:

• Empty saucer/cachepot water

• Loosen the top 2–3 cm of soil gently (helps airflow)

• Move to bright, indirect light

• Give it space so air can circulate

• Pause watering until the pot is noticeably lighter

If the smell persists after a proper dry-down, it’s usually time to repot.

Why Smelly Soil Often Brings Fungus Gnats

Fungus gnats love damp topsoil. Smelly compost doesn’t always cause gnats, but both problems share the same root cause: soil staying wet too long.

If you’re seeing tiny flies around the pot, you can also read Fungus Gnats.

Trusted Advice: Why Waterlogged Soil Causes Problems

According to University of Minnesota Extension guidance on overwatering and root health, oxygen-poor, waterlogged compost is a common reason indoor plants decline even when the soil looks “fine” on top.

FAQs About Why Indoor Plant Soil Smells Bad

Is a bit of compost smell normal?

Yes — a mild earthy smell is normal. Strong sour, musty, or rotten smells aren’t, especially if they worsen after watering.

Can I just add cinnamon or charcoal to stop the smell?

It may mask the smell briefly, but it doesn’t fix the cause. Drying and drainage improvements are what work long term.

Will the smell go away on its own?

If it’s mild and you correct watering, it can fade in days. If it keeps returning, the compost is likely stale and needs replacing.

Does smelly soil always mean root rot?

Not always, but it can be an early warning sign. If the plant is wilting in wet soil, inspect roots.

How do I stop it happening again?

Use drainage holes, empty saucers, water only when partly dry, and refresh compost before it breaks down into a dense, soggy mix.

Final Thoughts on Why Indoor Plant Soil Smells Bad

Most of the time, why indoor plant soil smells bad comes down to one thing: the pot isn’t drying properly. Fix watering first, remove standing water, and improve drainage so roots get air again. If the smell is strong or keeps returning, repotting into fresh, free-draining mix is the fastest reset.

Related Articles

• Prevent Mold in Indoor Soil

• Why Indoor Plants Turn Yellow