The Surprising Reason You Have Mould Around Your Windows (It’s Not Just Condensation)

If you’ve ever noticed mould creeping around your windows or doors, your first thought was probably condensation. It makes sense—warm indoor air hits cold glass, moisture forms, and before long, mould follows. But here’s the surprising part: condensation isn’t always the only culprit.

Sometimes, the greenery you love so much could be playing a bigger role than you realise. Certain plants naturally release moisture into the air, while others trap dampness around walls and frames. Together, they can create the perfect little pocket of humidity where mould thrives.

So, if you’ve been faithfully wiping down your windowsills and still find mould coming back, your plants might be quietly working against you. In this blog, we’ll look at how plants contribute to mould growth, which species are most likely to encourage it, and what you can do to enjoy your greenery and keep your home mould-free.

Why windows and doors are mould hotspots

If mould were a plant, its “potting mix” would be: moisture + something to feed on + still air. Windows and doors often deliver all three—sometimes every single day—so they become the first places you notice spots or musty smells. Here’s why.

1. Condensation: The everyday moisture maker

Think of a cold drink “sweating” on a warm day. The same thing happens when warm, humid indoor air touches a cool surface like window glass or a metal door frame. When the surface is cold enough, the water in the air turns into droplets—this is condensation.

• Cold surfaces: Single glazing, aluminium frames, and uninsulated edges get colder than the room. They “collect” water first.
  

• Humid rooms: Bathrooms, kitchens, and laundries add lots of steam. In tropical/wet seasons, the outdoor humidity keeps indoor air moist too.
  

• Air-con: Air-conditioning cools nearby surfaces. If the room air is still humid, you can get condensation even in hot weather.

Quick explainer: Air always holds some water vapour. When it touches a surface at or below its dew point (the temperature where air can’t hold that vapour anymore), the water drops out as liquid. That liquid = mould’s invitation.

2. Still air: Tiny pockets where moisture lingers

Mould loves stagnant air because damp surfaces dry more slowly. Windows and doors easily trap these pockets:

• Curtains and blinds pressed against glass stop airflow.
  

• Furniture close to a window wall (beds, wardrobes, couches) slows drying.
  

• Draft stoppers and closed rooms reduce natural air exchange, so moisture hangs around.

3. Mould food sources: Dust + paint + timber

Mould isn’t picky. It feeds on tiny organic residues most homes have:

• Dust, pollen, and skin cells on sills and frames.
  

• Soap residue and cleaning product films near bathroom windows.
  

• Timber, old putty, silicone, and paint binders—all offer organic components mould can digest.

When condensation mixes with any of these, you’ve got a damp, slightly dirty film—prime real estate for mould to colonise.

4. Leaks and micro-leaks: Water you don’t see (at first)

Condensation isn’t the only moisture source. Wind-driven rain, hairline gaps in sealant/caulking, or worn weatherstrips can let water creep into frame cavities or under sills. And in Australia, the wet season makes this even more likely—heavy downpours and humid conditions mean water can sneak into even the smallest gaps, leaving windows and doors damp for days at a time. If those areas don’t dry properly, mould has the perfect opportunity to settle in.

• Blocked weep holes in window frames stop water draining out, so it pools inside.
  

• Flat or poorly sloped sills hold water.
  

• Over time you see peeling paint, swollen timber, bubbling, or a persistent musty odour—classic signs moisture is sitting where it shouldn’t.

5. Temperature differences at the edges

Even on the same pane, the edges and corners are often colder (thermal bridging), so droplets bead there first. That’s why mould patches often trace the frame lines or appear where the glass meets the seal.

6. Daily life keeps “re-feeding” the problem

Showers, cooking, indoor drying of laundry, boiling kettles—these add moisture back into the air every day. If windows/doors don’t dry between these routines, you get a repeat cycle: wet → slow to dry → mould.

What to look for (early warning signs)

• Morning fogging or water beads on glass/frames
  

• Damp sills, dark lines in silicone, or black/green specks in corners
  

• Musty smell around curtains/blinds
  

• Peeling paint, soft timber, or bubbling near the frame
  

• Condensation marks where curtains touch the glass

Read related article: Mould or Mildew? How to Tell the Difference & What to Do

The role of plants in mould growth

Plants are often seen as the ultimate “healthy home” addition. They freshen up a room, look beautiful, and in some cases even help improve indoor air quality. But what many people don’t realise is that plants can also play a role in mould growth, especially when placed too close to windows or doors.

Plants release moisture into the air

All plants go through a process called transpiration—it’s how they release excess water from their leaves. In practical terms, that means every time you water your plants, a portion of that moisture doesn’t just stay in the soil; it ends up in the air around them.

When plants sit near windowsills or doors, that extra moisture adds to the dampness already caused by condensation or leaks.This creates a humid little pocket of air where mould spores can thrive.

Moisture in the soil adds to the problem

It’s not just the leaves—wet soil in plant pots can also release humidity into a room. If you keep plants sitting in trays of water or regularly overwater them, you’re creating a small but constant source of dampness right by your window frames. Mould doesn’t just grow on walls; it can appear on potting soil, trays, or the sill beneath them.

Outdoor plants and trapped dampness

It’s not only indoor greenery to be mindful of. Dense shrubs, bamboo, or climbing plants growing too close to exterior windows or doors can trap moisture against the walls. Without sunlight or airflow to dry the area, this lingering dampness seeps into window frames and sills, giving mould an easy foothold.

Why it matters for mould

• Local humidity spikes: Even a single peace lily or fern on a windowsill can increase humidity in that spot.
  

• Still air: Plants placed flush against windows or grouped tightly together can restrict airflow, slowing drying times.

Combine condensation, restricted airflow, and extra humidity from plants, and you’ve got all the ingredients mould needs.

In other words, while plants make our homes feel more alive, where you place them—and how you care for them—can make the difference between a fresh, green corner and a mould-prone one.

Common moisture-retaining plants linked to mould

Not all plants are the same or contribute to mould growth. Some species release more water into the air, thrive in damp conditions, or have thick foliage that traps moisture. When placed near windows or doors—where condensation is already common—these plants can tip the balance from fresh and green to damp and mould-prone.

1. Ferns (Boston Fern, Maidenhair Fern, Bird’s Nest Fern)

• Ferns are incredibly popular in Australia, especially in bathrooms, shaded patios, or hanging baskets.
  

• They are humidity-loving plants, releasing lots of moisture through their leaves while sitting in damp soil.
  

• Perfect for greenery… but also perfect for creating a mould-prone microclimate if placed near windows.

2. Peace Lily

• A staple in many Aussie households, peace lilies are prized for their low-light tolerance.
  

• They need consistently moist soil and release water vapour as they grow, which adds to indoor humidity around windowsills.

3. Palms (Kentia Palm, Areca Palm, Parlor Palm)

• Indoor palms are very common in Australian living rooms and offices.
  

• They have high transpiration rates and their wide fronds can block airflow near windows, creating still, damp pockets of air.

4. Tropical, Large-Leaved Plants (Monstera, Philodendron, Elephant Ear)

• Big, bold plants like monstera or philodendron are trendy in Australian homes.
  

• Their broad leaves release more moisture and cast shade, making it harder for nearby areas to dry out.

5. Bamboo (including ornamental and screening bamboo outdoors)

• Frequently used in Aussie backyards as privacy screening or landscaping.
  

• Bamboo grows dense, holds lots of water, and can trap moisture against walls and windows, especially in humid or rainy seasons.

6. Tree ferns (Cyathea, Dicksonia)

• Common in shaded gardens and patios, they thrive on constant moisture and create damp zones nearby.

7. Lilly Pilly hedges

• Popular screening plants in Aussie yards. Their dense foliage can trap humidity and shade walls/windows, slowing down drying.

8. Umbrella Tree (Schefflera)

Widely grown indoors and outdoors, with large leaves that both release moisture and create shaded, humid corners.

Moisture-loving plants like ferns, peace lilies, palms, bamboo, and certain Aussie natives are best kept away from your windows and doors—or balanced with good airflow and careful watering.

Plants less likely to encourage mould

Some species are naturally better suited for keeping indoor spaces fresh without creating the damp, humid environment mould loves. These plants typically store water in their leaves, stems, or roots, meaning they don’t release as much moisture into the air through transpiration. They also require less frequent watering, which reduces the chance of lingering damp soil or overflowing trays.

1. Succulents

Succulents are the ultimate low-maintenance option. They retain water in their fleshy leaves and only need a light watering every now and then. Because they don’t constantly release moisture into the air, they’re far less likely to create humidity pockets near windows. Plus, they thrive in sunny spots, making windowsills an ideal location.

2. Cacti

Similar to succulents, cacti are drought-tolerant and need very little water. Their ability to survive in dry environments means they add greenery without adding unnecessary moisture. For people in humid parts of Australia, cacti are a safe bet if you want plants close to windows.

3. Snake Plant (Mother-in-law’s Tongue)

Snake plants are hardy, stylish, and excellent for low-light conditions. Unlike tropical plants, they don’t need constantly moist soil and release very little water vapour. They’re perfect for bedrooms and living rooms where you want greenery but need to keep humidity levels in check.

4. Zanzibar Gem (ZZ Plant)

The ZZ plant is another tough, low-maintenance favourite. It stores water in its thick roots and waxy leaves, which makes it resistant to overwatering and less likely to create damp soil. It’s a great option for Aussie households that want greenery but don’t want to babysit plants—or risk mould growth near window areas.

Why these plants are mould-friendly (for you, not for spores):

• They require minimal watering, reducing damp soil.
  

• They retain moisture internally instead of releasing it into the air.
  

• They thrive in sunny or semi-shaded spots without constant humidity.
  

• Their smaller size and tidy growth mean they don’t block airflow around windows and doors.

How to prevent plant-related mould around windows

The good news is you don’t need to give up your beloved greenery to keep your home mould-free. With a few smart adjustments, you can enjoy plants indoors and outdoors without creating the damp, humid environment that mould thrives on. Here’s how:

1. Rethink plant placement

• Keep moisture-loving plants (ferns, peace lilies, palms) away from windowsills and doorframes where condensation is common.
  

• Instead, place them in rooms with better airflow or move them slightly further into the room.
  

• For outdoor plants, trim back dense hedges, bamboo, or shrubs that press against exterior walls and windows. This improves sunlight and airflow, helping surfaces dry faster.

2. Water wisely

• Overwatering is one of the biggest causes of indoor dampness. Let the soil dry slightly between waterings and empty saucers or trays of excess water.
  

• Choose pots with good drainage to prevent water pooling.
  

• For plants that like consistently moist soil, balance their placement with airflow—avoid tucking them into dark, closed corners near windows.

3. Improve air circulation

• Open windows regularly to let fresh air move through. Even a short burst of airflow helps dry surfaces.
  

• Don’t pack too many plants tightly together—leave space between them to prevent humidity from building up in still pockets.
  

• Consider a small fan or air purifier in areas that feel damp or where you keep lots of greenery.

4. Keep surfaces clean

• Wipe down windowsills and frames weekly to stop moisture and organic debris from building up.
  

• Use a safe mould-prevention product such as the SAN-AIR Surface Mould Remover Spray or SAN-AIR Surface Wipes to clean without harsh chemicals or toxic fumes.

5. Add ongoing mould protection

Even with good care, mould spores are always floating in the air. To stop them from settling in plant corners, pair your routine with continuous prevention:

• Place SAN-AIR Reactive Gels near windows, doors, or plant clusters. These gels release a safe, plant-based vapour that actively targets mould spores and bacteria in the air.
  

• They work particularly well in low-airflow areas where humidity tends to linger, creating an extra layer of defence against mould around your greenery.

Options include:

• SAN-AIR V3R Split System Reactive Gel – ideal for smaller spaces or near your air conditioner.
  

• SAN-AIR Caravan & Boat Storage Reactive Gel – perfect for larger rooms or areas with more plant coverage.

• SAN-AIR V3R Air Handler Reactive Gel – best for bigger air conditioning or HVAC systems where mould risk spreads through airflow.

When outdoor plants are the problem

It’s easy to focus on indoor greenery when you think about mould near windows and doors, but what’s happening just outside your home can be just as important. Outdoor plants, especially when planted too close to walls or window frames, can trap moisture and create the perfect environment for mould to thrive.

Dense hedges and shrubs

• Popular choices like lilly pilly hedges or thick shrubs provide privacy but can also press right up against walls and windows.
  

• Dense foliage blocks sunlight and airflow, meaning surfaces stay damp for longer after rain or morning dew.
  

• In Australia’s wet season, these areas can stay humid for days, giving mould spores plenty of time to settle.

Bamboo and fast-growing screens

• Bamboo is a common landscaping choice for creating natural screens.
  

• It’s highly water-hungry and grows in dense clumps that trap moisture against walls and windows.
  

• Without regular trimming or spacing, bamboo can create long-term dampness problems right next to your home.

Large trees and overhanging branches

• While shade is welcome in summer, large trees that hang over roofs and windows can block air circulation and sunlight.
  

• Fallen leaves and organic matter around sills and gutters increase mould’s food supply, making the problem worse.

How to prevent outdoor plant-related mould

• Trim regularly: Keep hedges and shrubs at least a small gap away from walls and windows to allow airflow.
  

• Choose wisely: Avoid planting fast-growing, water-hungry species (like bamboo) right against the house.
  

• Clear debris: Sweep away leaf litter and organic matter from sills, gutters, and around the base of windows.

• Check drainage: Ensure downpipes, drains, and garden beds don’t pool water against the house.

Conclusion

Condensation is often blamed for mould around windows and doors, but that is not always the case. The plants you keep—both indoors and outdoors—can quietly raise humidity, trap moisture, and create the perfect microclimate for mould to thrive. From peace lilies and ferns inside to bamboo and dense hedges outside, greenery can unintentionally feed mould growth if it’s not placed and cared for carefully.

But that doesn’t mean you give up your plants entirely. By choosing low-humidity varieties, spacing and trimming foliage, watering wisely, and keeping airflow moving, you can strike a balance between enjoying greenery and protecting your home. Pair those habits with ongoing mould-prevention support, and you’ll keep your windows fresh, clear, and mould-free all year round.