My garden decking was covered in grime and algae after winter, but this miracle outdoor cleaner made it look like new again – no scrubbing or pressure washer needed

With warm weather incoming, I was desperate to get my outdoor decking area set up and back in action again after a gloomy winter. But before I could get the garden furniture back out, my deck area needed some attention. It was looking pretty grimy all over, but my big concern was the dark patches of algae that had appeared in quite a few places, which looked really unsightly.

The general grime wasn’t too much of an issue - last summer I scrubbed it down with soapy water and a nylon brush, and it came up fine (though it was a bit back-breaking to do). But the areas of algae were a different story. I ended up on my hands and knees scrubbing at them with a scourer, tried bleach and white vinegar, but nothing shifted them.

Being given some Monty Miracle Complete Outdoor Cleaner, £21.95 for 2 litres at Amazon, to try out, which is one of the best patio cleaners in our guide, I’ll admit I was hopeful it would work, but I was slightly doubtful. But after testing it out, I’m totally impressed with the results.

One of the reasons I chose composite decking a couple of years ago was because I thought it was maintenance-free compared to the old timber deck I had before, but I’ve since discovered that it does need regular maintenance, as algae can be a problem, so it's important to know how to clean composite decking correctly.

After hours spent scrubbing the deck last summer and not being able to get rid of the algae patches, I’d resigned myself to them, strategically arranging plant pots to cover them up where I could.

What appealed to me about Monty Miracle Complete Outdoor Cleaner was that it promises to cut through grime on pretty much any outdoor surface (including composite decking and paving slabs) in just 10 minutes, with no heavy scrubbing involved and with no need to use a pressure washer.

Having seen reviews of the cleaner on TikTok, the results certainly looked impressive, but I wasn’t sold before trying it out myself.

Before getting started with the cleaner, there’s a little bit of prep involved first. Monty Miracle does have de-oxidant properties (which can cause damage to plants and aquatic life), so it's important to protect any areas you don’t want to affect, such as lawns, plants, ponds, bushes, etc. Simply hose the protected area with water before and after application.

I also used old dust-sheets to cover the grass edges adjacent to the deck area to be extra cautious. And it’s also super-important to remember that children and pets should be kept inside and away from the cleaner before it’s rinsed away.

Before starting, I moved all my containers off the deck (except for a couple of really heavy planters) and then swept down the decking with a broom so it was clear of any leaves, dirt and loose debris.

What you'll need

• Garden spray pump bottle - to apply Monty Miracle Outdoor Cleaner with, there are plenty of spray pump bottles at Amazon
• Rubber gloves - to protect your hands
• Protective eyewear - to ensure spray doesn't accidentally get into your eyes, safety goggles like these from Screwfix are a must
• Garden hose - for preparation and rinsing
• Soft-bristle broom - for agitating the cleaner
• Old clothing to wear - the cleaner will damage your clothes if it gets on them

As it was a warm day and the decking area was very dry, it’s advised that you spray the area with a light coating of water first. This helps the cleaner stay on the surface where you need it to clean, rather than being absorbed into the decking. You can use the garden hose for this, making sure that the surface is wet but not waterlogged.

The cleaner can still be applied on damp surfaces if it's a rainy day, but if the area is swamped with excessive water, the effects will be weakened.

To start, simply pour the cleaner into your pump bottle (remember to wear rubber gloves when doing this). There’s no need to dilute the cleaner; it’s ready to use as it is.

It’s advised to do a patch test on a discreet area first, simply spraying the cleaner on, agitating with a soft brush and leaving for 6-10 minutes. I thought I’d jump right in and spray it on an area that was green in the hopes that it would help remove algae from the decking.

After leaving the cleaner for 10 minutes, the green area was definitely lighter, but still visible. Taking this as my patch test, I then set about applying the cleaner all over the deck, as well as re-applying it to the patch test area again.

As it was a warm day, I found it helped to work in sections, so I divided my deck up into quarters, spraying on the cleaner, gently agitating with the brush, before moving onto the next section. Agitating helps provide a uniform clean all over, but there is absolutely no need to scrub at the surface.

After leaving the cleaner to work for 10 minutes, it was time to rinse it off with the garden hose. The cleaner is completely neutralised by the water and is 100% biodegradable, so it can be hosed off onto the grass or into soil. It’s advised to hose down all surrounding greenery too afterwards, just to be sure there is no damage to garden borders or plants caused by splashing.

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After hosing off the cleaner, I could see immediately that all the general surface grime had disappeared. And the dull tinge that had built up over winter was lifted. Even the areas of algae were noticeably much lighter (though still faintly there).

For very stubborn areas, it’s recommended to reapply the cleaner and work into the area again with your brush (no need for scrubbing) and allow another 10 minutes on the surface.

So I did this on all the areas where the algae hadn’t quite disappeared, and I was amazed by the results. After hosing off with clean water again and leaving to dry in the sunshine, all traces of green have disappeared. I am super-impressed.

To clean my deck area, I used half of the 5-litre container, leaving half a container that can now be used to clean my paved patio area at the top of the garden. The whole process was finished in under an hour, involved no back-breaking scrubbing or harsh cleaning with a jet washer (which can damage composite decking), so I am very happy with the results all-round.

With the garden furniture now out of the shed, plants back in place again and everything set up on the deck, all I need is some more sunny weather so I can enjoy using the deck for the rest of the summer.

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