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Weeds on Paths and Paving

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The hard landscaping surfaces surrounding the house and in the garden, can range from loose gravel to a sea of concrete or tarmac, and these can all become infested with algae, moss and weed plants. The crustose forms of lichens such as Lecanora rupicola form white patches on paving and tarmac, and are extremely difficult to remove. Wooden decking is not a good choice in the British climate as it quickly develops a slppery film of algae so requires regular cleaning to keep it safe to walk on.
Algae and moss are the pioneer plants which can establish on a bare substrate, their spores are floating around in the wind and in rain-drops. As they grow they trap dust and plant debris which is blown in and builds up to provide a medium for more advanced plants to germinate. Left alone for a few years a large variety of plants will become established on a solid concrete surface. If there are any cracks or crevices, deeper-rooted plants can take hold, although if there is enough debris around they will form a dense mat of roots over the surface.

The rate of development of a film of algae on a solid surface depends on a number of factors. While light is required for them to grow, heat from the sun dries the surface and the its harmful effects inhibit growth. So shady areas are more prone to getting a film of algae or moss. Cutting back overhanging trees or shrubs can reduce the rate of growth. Poorly drained areas are also more prone to infestation.

In areas which are constantly shaded a solid relatively smooth surface can be installed so that any debris and developing algae are easily removed. Scrubbing with a brush and water is quite laborious, and using a power washer can be slow as well as damaging to paving by pitting the surface or washing out grouting. There are chemical treatments, but care is needed to avoid damage to adjoining grass or flower beds where the run-off might settle.
Sodium Hypochlorite (bleach) is a popular chemical used for cleaning paths and driveways; a more economic source is the bulk product available from farm suppliers. It is usually watered or sprayed on. After a day or so the algae and moss will have died and can be left to decay naturally or scrubbed away. Excess amounts of moss can be scraped off with a spade before application; dead material is more difficult to remove if it is allowed to dry up. If left it will act as a medium for seeds to germinate in. It is best to use this sort of treatment regularly as the initial film is developing, rather than allowing a carpet of moss to grow.

Gravel is an ideal surface for drives and paths as it allows water to soak away, so it doesn't put a strain on drainage systems. After a few years it can become clogged with debris and softer stones are crushed by vehicle tyres so fill the spaces. Seeds find this an ideal medium for germination. Regular raking will keep the surface looser and discourage the weeds.
Leaves must always be removed so that they cannot break down to add to the debris, a blower is probably the best tool for the job. For large amounts rake the bulk up first, then use the blower to gather up the remainder. The strong air current will lift damp leaves stuck to the surface.

The cement-based grout between paving slabs attracts a moss which prefers the alkaline conditions - it is the same moss that grows in little hummocks on cement roof-tiles and slates. Smaller areas can be cleared using the edge of a garden fork scored along the grout space.
Block paving does not have grouting between the bricks, but the narrow crevice soon becomes host to moss and weeds. These can be removed with a hooked weed-knife or a special wire brush with the bristles arranged in a V shape. Keeping the crevices topped-up with clean, dry sharp sand will discourage the development of any unwanted growth. Leaving the sand spread out on a warm, sunny day for a while will allow it to dry out before brushing it over the bricks, so that it will flow down into the crevices fully.

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Weeds   Weed Prevention   Weed Removal   Weedkillers

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