How to Clean Garden Stones: A Complete Guide for Removing Dirt, Algae and Stains

Incorporating stone into your landscape design is a trendy, low-maintenance choice, albeit one that occasionally requires cleaning. The frequency of cleaning depends on the specific stone type and its location. Light-hued stones are prone to discoloration, often exhibiting a green tint caused by surface algae.

Stones situated in moist or shaded areas are particularly susceptible to quicker algae growth, given their slower drying rate. Softer, more porous materials like limestone, sandstone, and marble show signs of discoloration faster than more durable options like granite, flint, or quartzite. For instance, apricot gravel composed of quartz, which was installed three years prior, exhibits negligible discoloration. Conversely, pink marble flamingo chippings in the same garden have shown significant greenish discoloration over the same period.

Implementing a weed barrier fabric underneath gravel or chippings can prolong the cleanliness of stones, as it blocks sunlight and prevents the growth of weeds or moss between the rocks. However, despite the usage of weed barriers, numerous cleaning methods exist for gravel, pebbles, cobbles, and boulders. The chosen approach will depend on the stone's composition and the level of effort you're willing to invest.

Easiest Cleaning Methods

The simplest method to clean stone is by using a power washer, although it may scatter smaller gravel pieces. A garden hose with a high-pressure nozzle can also effectively remove dirt and accumulated algae. For more delicate gravel, a softer water stream or shower setting should be used to prevent damage to the material.

A combination of water and dish soap or vinegar, applied with a brush, can be used for cleaning aggregates of any size. Choose a stiff-bristled brush and energetically scrub each stone to dislodge adhered dirt or algae, following up with a thorough rinse using a hose. Repeat this process as required for heavily stained areas.

For gravel driveways or pathways blanketed in mud, extract a portion of the stone and sieve it to dislodge dirt clumps. Following that, clean the sifted gravel with a hose before placing it back. While this method is effective, it could be time-consuming when applied to expansive areas.

Specialized Cleaning Products

There are also cleaners made specifically for restoring the colour of discoloured paving stones, wall rock, pebbles and gravel. These often contain detergents, mineral salts and other active ingredients tailored to dissolve and remove organic growth, mud and grime.

Some popular stone cleaning products to try include:

Always follow product instructions carefully and test on a small, inconspicuous area first to ensure it won't etch or discolor the stone. Avoid using acidic cleaners like vinegar on calcite-based stones like limestone or travertine which can damage the finish.

DIY Cleaning Solutions

For a more natural and often cheaper option, you can mix up your own stone cleaning solutions using common household products:

Baking Soda - Mix 1⁄2 cup baking soda with 1 gallon of water and apply to dry stones with a stiff brush. Let sit 15 minutes before rinsing clean. The mild alkalinity helps dissolve organic growths.

Washing Soda - Also called sodium carbonate, washing soda is more alkaline than baking soda. Mix 1 cup washing soda with 1 gallon of warm water and scrub onto stones. Rinse thoroughly after 15-20 minutes.

Borax - This naturally occurring mineral has antiseptic properties to kill algae and draw out deeply ingrained stains. Make a paste with 3 parts borax to 1 part lemon juice and scrub it onto affected areas. Rinse off after several hours.

Hydrogen Peroxide - Its bubbling reaction helps lift stains and kill algae. Spray full strength hydrogen peroxide onto dry stones and let fizz for 15 minutes before rinsing. Be careful handling concentrated solutions.

Vinegar - The acid in vinegar kills moss and algae. Use undiluted white vinegar in a spray bottle for minor growth. For tougher jobs, mix 1 part vinegar with 2 parts water and scrub onto stones with a stiff brush. Rinse thoroughly after 15 minutes. Avoid using vinegar on acid-sensitive stones.

For best results, thoroughly pre-wet the area to be cleaned, apply the cleaning solution to dry stones, let soak the recommended time and rinse off with a high pressure nozzle. Wear gloves and eye protection when handling chemicals.

Tips for Cleaning Large Areas

For cleaning big areas like gravel driveways or landscaped beds covered in debris and organic growth, a few tips can make the work easier:

  • Use a pump sprayer rather than hand brushing to quickly pre-wet and apply cleaner over more square footage. Look for a high capacity tank with an adjustable nozzle.

  • Opt for concentrated cleaners that can cover more ground per mixed gallon. Follow label dilution rates carefully.

  • Divide the area into smaller, manageable sections and systematically work through each one. This prevents missing spots and having to backtrack.

  • Use a stiff push broom to efficiently scrub cleaner over all stones rather than hand brushing. Scrub and rinse each section before moving to the next.

  • Rinse thoroughly with a pressure nozzle. Test different angles and aim water flow off the stones rather than forcing water through for best results.

  • For extremely dirty gravel, remove a few inches at a time with a small excavator or loader and sieve clean before replacing. Replenish with a fresh layer of gravel as needed.

  • Schedule cleanings in spring and fall when temperatures are moderate. Heat can dry cleaners too fast before they have time to work.

  • Always wear protective eyewear, gloves, shoes and clothing appropriate for the chemicals used. Follow safety directions.

Alternative Cleaning Methods

If you're still struggling to get your garden stones clean, a few more intensive methods may help:

Pressure Washing - Rent a heavy duty gas pressure washer with a wide fan nozzle to blast away stubborn dirt and stains. Take care around softer stones.

Sand Blasting - Professionally sand blasting etches away the outer stained layer while leaving a clean finish. Results look freshly cut but can be costly.

Flame Weeding - Passing a handheld propane torch flame briefly over the stone surface carbonizes and destroys organic growths like algae or moss. Use extreme caution.

Sealing - Applying a penetrating sealer after cleaning helps shield stones from future dirt, oils, mould and mildew stains. Reapply annually.

Whitewashing - For old, severely discoloured paving stones, a whitewash made of hydrated lime, salt and water can coat and renew the look of worn surfaces. Rinse immediately if applied to unintended areas.

Replacing Stones - Ultimately, stained or damaged decorative aggregates may need partial or full replacement to restore the appearance. Remove and dispose of old stones before relaying fresh, clean materials.

By tailoring your approach using the right methods and products for your specific garden stones, keeping them looking clean and bright doesn't have to be difficult. With a little seasonal attention, you can maintain beautiful hardscaping features despite weathering and organic growth. Test products and techniques in small areas first and always closely follow label directions when using commercial cleaners. Your efforts will be rewarded with renewed stones you can continue enjoying for years to come.

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