Mildew on patio cushions comes off with white vinegar, baking soda, or a mild detergent solution — the method depends on how deep the growth has set in and what your cushion fabric can handle

Mildew grows on cushions when moisture sits on the fabric for days without drying. It starts as dark spots or a fuzzy coating, usually on the underside where air doesn't circulate. The good news: surface mildew washes away easily. The harder part is keeping it from coming back, which means understanding why your cushions stay damp.

Before you clean, check your cushion's care tag. Most outdoor fabrics are solution-dyed acrylic or polyester and handle vinegar and detergent well. If the tag says "dry clean only" or the cushion is vintage or delicate, test any cleaner on a hidden corner first. Mildew itself won't spread to other cushions if you store them separately, but the dampness that caused it will affect anything stored the same way.

Key Takeaways

  • White vinegar (undiluted or mixed 1:1 with water) kills surface mildew on most outdoor cushion fabrics without bleaching or damage.
  • Baking soda paste works for light mildew and absorbs odor; detergent solution handles heavier growth and embedded stains.
  • Scrub gently with a soft brush, rinse thoroughly, and dry completely in sun and air before storing to prevent regrowth.
  • Mildew returns if cushions stay damp — use breathable storage, elevate them off the ground, and bring them inside during rainy seasons.

Cleaning with white vinegar for light to moderate mildew

White vinegar is the first choice for most mildew because it kills the spores without bleaching acrylic or polyester fabrics. Use it undiluted for stubborn spots, or mix it 1:1 with water for a gentler approach on lighter growth. Spray or pour the vinegar directly onto the affected area, let it sit for 10 to 15 minutes, then scrub with a soft-bristled brush — a toothbrush works for small spots, a deck brush for larger areas.

After scrubbing, rinse the cushion thoroughly with clean water from a hose or bucket. Vinegar smell fades as the cushion dries, but if you want to speed that up, rinse a second time or spray the damp cushion with a 1:1 mix of water and baking soda. Lay the cushion flat in direct sun and air to dry completely — this usually takes 4 to 8 hours depending on humidity and thickness. Do not store it until it is completely dry to the touch, including the interior.

Using baking soda paste for light mildew and odor

Baking soda works well if the mildew is light (just a few spots) and you want to absorb musty smell at the same time. Mix baking soda with a small amount of water to form a thick paste — about 3 parts baking soda to 1 part water. Spread the paste over the mildewed area, let it sit for 30 minutes to an hour, then scrub gently with a soft brush.

Vacuum or brush off the dried paste, then rinse the cushion with water until no white residue remains. Baking soda is mild enough that you can repeat this process if some mildew persists. As with vinegar, dry the cushion completely in sun and air before storing. This method is slower than vinegar but gentler on delicate fabrics and leaves the cushion smelling fresher.

Detergent solution for heavy mildew and staining

If mildew has been growing for weeks and left dark stains, a mild detergent solution cuts through the buildup better than vinegar alone. Mix 1 tablespoon of liquid dish soap or laundry detergent with 1 quart of warm water. Soak the affected area with this solution, let it sit for 15 to 20 minutes, then scrub with a soft brush using circular motions.

Rinse thoroughly — this is important, because soap residue left on the cushion can trap moisture and cause mildew to return faster. Rinse at least twice with clean water, wringing or pressing out excess water as you go. Lay the cushion flat in direct sun to dry. If stains remain after drying, you can repeat the process, but avoid scrubbing so hard that you damage the fabric weave.

Drying and preventing regrowth

The step most people skip is the complete dry. Mildew returns within days if you store a cushion that still feels slightly damp inside. After cleaning, place the cushion in direct sunlight with good air circulation — a sunny spot on the lawn or deck works better than a shaded patio. Flip it every 2 hours if possible so both sides dry evenly. In humid climates, this can take 8 to 12 hours or even overnight.

To prevent mildew from coming back, store cushions in a way that lets air move around them. A breathable storage bag (not a sealed plastic bin) or an open shelf in a dry garage works. If you live somewhere with long rainy seasons, bring cushions inside rather than leaving them outside. Never stack damp cushions or store them in a closed container — the trapped moisture is what mildew needs to grow. If your patio stays wet for days after rain, consider storing cushions indoors during those months.

When to replace a cushion instead of cleaning

If mildew has penetrated deep into the foam core and the cushion smells musty even after cleaning and drying, replacement may be the better choice. Mildew inside foam is hard to kill completely and will return quickly. Signs that a cushion is too far gone: the smell does not fade after 24 hours of sun drying, the foam feels soft or breaks apart when you press it, or the mildew reappears within a week of cleaning.

Outdoor cushion covers are also replaceable if the fabric is damaged or stained beyond what cleaning can fix. Many retailers sell replacement covers that fit standard cushion sizes, and they cost less than a new cushion. If you are replacing cushions, choose ones with removable, washable covers — this makes future cleaning much easier and extends the life of the cushion itself.

Storage tips for humid climates

In areas with high humidity or frequent rain, how you store cushions matters as much as how you clean them. Elevate cushions off the ground on a shelf or rack so air can flow underneath — sitting directly on concrete or wood traps moisture. Use a breathable storage bag or cover, not plastic, which holds humidity inside. If you use a storage box, drill small holes in the bottom and sides to allow air circulation.

During the off-season, store cushions in the driest place available — a heated garage, shed, or basement is better than an unheated outdoor structure. If you must store them outside, place them under a roof overhang where they stay dry but still get air movement. Check them once a month during storage; if you notice any smell or spots, pull them out and dry them in the sun again before putting them back.

Frequently Asked Questions

Can I use bleach to clean mildew off cushions?

Avoid bleach on most outdoor cushions. It can fade solution-dyed acrylic and polyester fabrics and may weaken the fibers over time. Vinegar and detergent are safer and work just as well on mildew. If your cushion is white and you want to use bleach, test it on a hidden corner first and dilute it heavily — no more than 1 part bleach to 10 parts water.

How long does it take for mildew to come back after cleaning?

If the cushion is stored dry and in good air circulation, mildew should not return for months. If it comes back within a week or two, the cushion is not drying completely before storage, or it is being stored in a damp location. Move it to a drier spot or bring it inside during humid seasons.

Is mildew on cushions dangerous to breathe?

Light mildew on outdoor cushions poses minimal risk for most people. However, if you have asthma, allergies, or a weakened immune system, mildew spores can trigger symptoms. Clean cushions before using them, and if you are sensitive, consider storing them indoors or replacing them rather than cleaning repeatedly.

Can I wash cushions in a washing machine?

Check the care tag first. Some cushion covers are removable and machine-washable, but the foam core itself should never go in a washer — it will absorb too much water and take weeks to dry. If the cover is removable, wash it separately and dry the foam core in the sun.

What if the mildew smell stays after cleaning and drying?

Baking soda absorbs odor better than vinegar alone. Sprinkle dry baking soda on the cushion, let it sit for several hours or overnight, then vacuum it off. If the smell persists after this, the mildew has likely penetrated the foam, and replacement is the more practical choice.