Karcher T7 Patio Cleaner Stripped Algae from 25 Square Metres of Sandstone

A K5 pressure washer delivers around 145 bar at the lance tip. Fit the Karcher T7 T-Racer and that force is shared between two rotating jets inside an enclosed disc about 30 cm wide. Across 25 square metres of sandstone, the pace came out at roughly 40 minutes of steady walking, with far less sideways spray than a bare fan lance sends across legs, borders and nearby beds.

The first layer to lift was the black-green algal film, the slick coating that turns wet sandstone dangerous in autumn. The T7 removed that surface growth cleanly and left the patio with a much more even colour. Darker biological staining stayed in the deeper pores of the riven stone, below the top millimetre. On soft, porous sandstone, the cleaner strips the visible growth while organisms inside the pore structure can remain alive. That difference is what separates a patio that looks clean for six weeks from one that stays clear for six months.

Why the Algae Returns Quickly

Pressure washing removes what can be reached mechanically. Spores and growth sunk into sandstone have a better chance of surviving, especially where the slabs stay damp.

Sandstone holds water. A riven or sawn sandstone paver can carry 3 to 6 percent water by weight when saturated. That retained moisture supports green algae and the black growth often described as lichen. Clean the surface with a T7 in September, leave a shaded north-facing corner with poor drainage, and the film can be measurably back within two months.

Surface cleaners sell well because the before-and-after photograph is real, but that photograph only records the reachable growth. If cleaning stops at the pressure-washer stage, the patio can look finished while the biological source of the staining is still alive down in the pores, ready to spread back across the clean face.

A biocidal patio treatment changes that result. Sodium-hypochlorite-free products based on benzalkonium chloride, or a similar quaternary compound, are used to kill root growth inside the pore structure. Applied to a dry surface after the T7 has removed the bulk growth, then left to soak, this kind of treatment can stretch the clean period from weeks into a full season.

Wash with the T7, allow the stone to dry for a day or two, apply the biocide, then leave it in place. Immediate rinsing removes the residual protection. Sealing the sandstone after cleaning can extend the clean period again, although sealing a patio with live algae still in the pores traps the biological problem beneath the surface.

A freshly washed slab also hides one unresolved issue. The clean face of the stone does not show whether poor drainage is feeding the shaded areas that green up first, and that same standing water is often what rotted the fence post at the patio edge.

Sika Postfix Beside a Clean Patio

A patio can look newly restored while the fence beside it still leans. Where a post has rotted at the base, the usual repair is to reset it, and Sika Postfix offers a lighter, faster alternative to mixing concrete. One 20 litre bag of the two-part expanding foam sets a standard 100 mm post in roughly three minutes and reaches full load in about 30 minutes, compared with the day-plus cure of a postmix concrete collar.

Postfix weighs around 1 kg per bag. An equivalent postmix load is about 20 kg, so one person carrying material for six posts moves 6 kg of foam instead of 120 kg of postmix. The foam also drains, which matters when the original post failed because water pooled around the timber base inside a concrete collar.

The expansion helps in awkward holes. A slightly oversized or crumbling hole can still get a firm set because the foam fills irregular spaces without needing a precise wet mix.

Postfix costs several times as much per post as a comparable volume of postmix, so concrete wins on materials for a 20 post run. For one or two failed posts beside a patio that has just been cleaned, the saving is in labour, weight and mess.

Once the post is firm and the ground around it drains, the same reasoning about water and slumping applies to anything built to hold soil nearby.

A Raised Bed Fill That Holds Its Height

Raised beds often disappoint in the second year because the fill was too rich and too fine. A mix dominated by soft organic material compacts, and the surface can slump 15 to 20 percent below the top rail.

A more durable vegetable-bed blend is roughly 50 percent quality topsoil or soil-based loam, 30 percent well-rotted compost or composted bark, and 20 percent coarse grit or horticultural sand. The mineral fraction is what keeps the bed open and draining. Pure compost fill looks generous on delivery, then turns into a dense, airless mass within a season, leaving roots short of oxygen.

For a bed 1.2 metres by 2.4 metres and 30 cm deep, the fill volume is about 0.86 cubic metres. Ordering a full cubic metre of blended material covers settling and leaves a small amount for topping up in spring.

Peat-based multipurpose compost performs poorly as bulk fill. It can swing between waterlogged and hydrophobic, and it breaks down quickly. Composted bark or a loam-based John Innes No 3 used for the compost fraction gives a much steadier base over three or four seasons than stacks of cheap growbag compost.

Even the right blend fails if it goes over heavy clay that has been worked at the wrong time.

Clay Soil Needs the Right Moment

Heavy clay worked while wet smears into a solid, glazed pan that roots and water struggle to cross. Work a clay vegetable bed during a dry spell in spring or autumn, when a squeezed handful falls apart into fragments and the spade leaves rough faces instead of shiny smears.

Codling Moth Traps and the Hatch Window

A pheromone codling moth trap is a triangular delta trap with a rubber lure that mimics the female moth’s sex pheromone. Male moths are drawn onto a sticky base. Hung at head height in an apple or pear tree, one trap covers a small garden of up to about five trees.

The catch count is what tells you when to act. It marks when moth flight starts, and the spray or barrier window opens roughly 7 to 14 days after the first sustained catch, when eggs hatch and larvae begin moving toward the fruit.

Many gardeners treat the trap as the whole defence. In a small garden with one or two trees, a well-placed trap may reduce the male population enough to cut damage by itself. In a fruitier neighbourhood, moths can fly in from outside the garden, so the trap mainly acts as a monitor. Control then depends on a targeted treatment during the hatch window or a physical barrier such as cardboard bands around the trunk to catch larvae looking for a pupation site.

The lure degrades. A standard pheromone cap lasts around six weeks of active flight before it stops pulling strongly. The sticky base also clogs with debris and non-target insects.

Two lures across a summer, with one replaced mid-season, keep the count meaningful through both codling moth generations in a warm year. A trap left up all season on one old lure can give a falsely low count while the second generation damages the fruit.

Roses, Splash and Blackspot

David Austin roses planted along a patio edge often get blackspot because of splash. Rain, and sometimes overspray from a pressure washer, throws soil-borne fungal spores onto the lower leaves. In warm, wet weather, Diplocarpon rosae develops from there.

Control starts with removing infected leaves, including the fallen ones. The fungus overwinters on debris and reinfects plants from the ground up each spring.

Spacing and airflow carry more weight than many spray routines. A rose squeezed against a fence with little air movement dries slowly after rain and stays infectable for hours longer than a plant with open sides. Myclobutanil-based rose fungicides work best as preventive products, applied before symptoms appear and repeated through the wet stretch. They are poor rescue tools once half the leaves have yellowed and dropped.

Some David Austin varieties have genuinely strong blackspot resistance, while older, more romantic cultivars are often the worst offenders. If a rose defoliates every July despite repeated care, pull it out and plant a resistant variety in the same gap, then strip and bin every fallen leaf around it before the next spring flush starts the cycle again.