How to remove mold and mildew from artificial grass, and keep the strip dry

Three things, all at once: moisture, shade, and food. On the coast, moisture is a given from spring through fall; humidity sits near 85 percent before dawn and the wettest months run June to September. Shade comes from the house, the fence, a deck, a hedge, and it is why mold appears in strips and corners rather than across the yard. Food is the organic layer: pollen from March and April, leaf litter from the live oaks, dust, dog hair, whatever has settled into the fibers and started to rot. Take away any one of the three and it stops. The black patches page covers telling mold from algae, which need the same conditions and get the same treatment.

• A leaf blower and a stiff synthetic-bristle broom.
• A hydrogen-peroxide-based oxidizer or an algaecide labeled for artificial turf or outdoor synthetic surfaces. Products sold for roofs and siding are often bleach-based; read the label.
• A pump sprayer.
• A dry, overcast day, or an evening. Not rain, and not full sun, which dries the product before it works.

1. Remove the food. Blow the strip, then brush hard against the grain with the push broom to lift the organic layer out of the fibers. Blow again. What comes out is black and fibrous. This step is the one people skip, and it is the one that matters.
2. Rinse with the hose on a shower setting to carry the loosened layer down and out.
3. Let it drain ten minutes so the turf is damp, not flooded.
4. Apply the oxidizer or algaecide at label dilution, wetting the fibers down to the infill across the whole strip and a foot beyond the visible growth.
5. Dwell the label time, usually ten to twenty minutes. Keep it wet.
6. Brush against the grain again while it is wet, then rinse thoroughly.
7. Dry it out. Brush the fibers upright once more when dry so air moves through them. Pull anything sitting on the strip off it.
8. Repeat in two weeks. One round kills the surface growth; the second gets what was under it.

Treatment clears the growth. It comes back unless the strip stops being wet. Walk the strip after the next rain and look for the reason. A hedge or shrub against the fence blocks the wind; cut it back a foot. Deck skirting seals the space under the deck; open a panel. A downspout lands on the corner; add an extension. Water still standing an hour after rain means the infill has compacted or the backing is clogged with organic matter, which is the situation on the water pooling page and usually needs the infill loosened or replaced. The drying page has the rest.

• Chlorine bleach. Kills the surface growth, lightens the fibers, degrades the backing, kills the hedge, and leaves the organic layer for the next spores. It is the most common thing we get called to undo.
• A pressure washer. Blows the infill out of a strip that already drains badly.
• Vinegar alone. Browns the top layer of established growth and leaves the rest. Fine as a rinse after the oxidizer, not as the treatment.
• Skipping the brush-out. Oxidizer sprayed onto a thick organic layer is used up by the layer and never reaches the growth under it.

A strip along one fence is a Saturday. Growth across a whole shaded side yard, under a full deck, or anywhere the infill has gone black and crusted underneath it, is a power brush, a high-volume flush, the oxidizer applied with proper dwell and an antimicrobial to keep it from restarting. That is our algae and mold removal, included in a Premium Restoration from $299 for up to 500 square feet and $399 for up to 1,000, with the antimicrobial available as a $75 to $125 add-on on an Essential Clean. Shaded coastal yards usually need this once a year in spring, before the wet season starts.