Blast off: It’s out with the power hose on that mossy patio

It’s a time-consuming weekend task, but few outside jobs can match the satisfaction of transforming slimy green patios to their original form, writes Kya deLongchamps.

Blast off: It’s out with the power hose on that mossy patio

Reaching the front door, supplicant against the drizzle for months, we don’t generally notice the creeping blanket of microscopic botanic growth smothering walls, pathways and hard landscaping.

It’s a time-consuming, potentially grubby weekend adventure, but few outside jobs can match the instant satisfaction of transforming slimy green patios, decks, concrete walkways and steps to their original purity and colour.

Stone and concrete is a conglomerate of mineral rich materials on which tiny plants can happily feast when they are released by scuffs and wet weather. Eating away at the surface of a paving stone, lichen will not do any structural damage but it can suck out the colour of tinted stone in patches, even if you get the blighter off with repeated scrubs.

In sufficient depths and ranged across unsealed stones and slabs with no roughened tread to save us — after rain, a micro-environment of lichen, algae and tufts of soggy moss can be dangerously slippy. Some deliberate promotion of lichens is a popular way to soften the appearance of old stone sculpture, and even walling, but on walkways, control is crucial.

Surfaces and joints between paving stones, gifted any depth of ingression of dusty muck and green growth, will start to harbour larger vertical weeds, spoiling the look of those soft, mortar free joints.

If you have just installed paving or paths, start as you mean to go on, and brush them down regularly with a wire paving brush. Even the attrition of a good broom will keep most small plant life at bay, and you’ll burn 200-250 calories per hour doing the whole lot in one afternoon. Rake gravel regularly to turn it over, disturbing sly growth.

Occasionally give the whole lot a wash down with an acid-free soapy cleaner slopped into warm or cold water. Rinse off with your garden hose, brushing excess water that may harbour spores and seeds to your drains, avoiding planted areas with tender plants.

Work across joints filled with sand with a soft brush being careful not to clear them out too. Keep a bag of horticultural sand on hand, mixed with a little jointing stabiliser to lightly bind the grains, and gently re-fill areas as you go. Examine the efficacy of water run-off on your hard landscaping, as pooling water will promote unsightly green growth.

Lichen is a shy, slow bloomer, but moss, algae and those big flattened liverworts, are sexy little devils and spread rapidly if left untended. There are two approaches to beating the uglier, settled invader on established paving and paths (both in my experience will deliver a sheen of algae to the complexion).

The first is sheer, determined brush-muscle in league with some soap and/or heavy chemistry, or cutting a swathe through the muck with a dedicated power washer. It’s extremely important to weigh up what you are prepared to throw into the groundwater, as inevitably any solution will leech into the surrounding soil. Stick to dish-washing soap if you can, using muscle rather than toxicity to shift the dirt.

Path and patio cleaners use a solution of either benzalkonium chloride or various mild acid washes to kill moss and algae. Bleach and Jeyes Fluid Path & Patio is a favourite for the job, but use as little as you can get away with and wear rubber overalls, protective goggles and gloves to spare your skin and eyes.

The 1:1 or even 1:2 solutions advised for these solutions is very, very strong, and must be thoroughly rinsed off before pets or children go anywhere near the area. Just Patio and Concrete Cleaner is a natural surfactant (detergent) based on seaweed extracts that is non-caustic, non acidic and environmentally friendly. For a homemade solution, try baking soda and salt dissolved in a bucket of warm water, spritzing small weeds with neat, white vinegar.

Powerful Buy:

Pressure washers are a fantastic, versatile tool, and yet remain one of the most ill-advised pieces of powered equipment used in the garden. Deployed on everything from crumbling mortar to unsuspecting dogs and pet ponies, the unexpected force of litres per second jettisoning from a power washer can blow the joints out of walling and pavers, lift flakes of more delicate patio stones and earn you an equestrian kick up your horticulturals.

Match the force and pattern of the spray to the job, angle the lance to relieve the severity of the spray and keep moving in a sweeping motion, not bearing down on one area for any length of time. If you have reclaimed water from a water barrel — try using that.

Buying a machine:

You can choose from electrical or petrol models (electrical suit most domestic situations). The power of a machine intended for use on paving and decking should be in the area of 110-160 bar. The motor of a suitable machine will be around 1400-2,000 watts with a flow rate of water from 350-500l per hour. The real working pressure will be expressed as bar-rated pressure, as the pressure in the washer will start high and then modulate as you work. Using a trigger spray intelligently, your machine should save water on doing the same job with a standard garden hose.

Some models offer not only a dirt-blasting lance with variable spray heads, but a dedicated patio cleaner that rides lightly like a small hovercraft, scrubbing the surface with spinning jets under a splash guard. This can be glanced over gravel to clean that too without blowing stones all over.

Use the specialist detergent in the correct ratio for your machine. Expect to pay in the area of €150-€250 depending on model and stick to known quality brands such as Karcher, Vax, Nilfisk and Qualcast. Aldi had a special last Monday, a 150 bar, 2 200W washer at €99.99 — there may be some yet for sale.

Most stone, paver blocks and all aggregates are to some extent porous. Sealing their surface, especially patterned concrete with an appropriate product, will keep them looking fresher for longer and cut down on this hard labour and water works.

Again, always choose non-chemical control where possible, keeping that green monster tamed with regular maintenance and swift, effective drainage.

Finally, think about cutting back shadowing trees and shrubs, and clear away leaves and debris to let the sunshine and fresh breezes do the work for you.

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