How deep should mulch be laid and when will it need to be topped up?

Generally, I suggest a minimum depth of 50mm to 75mm but you should note that optimum depth will depend on the type and particle size of the mulching material used.

Light aids the germination of many weed seeds and any tiny seedlings receiving light will romp away, so the aim is to create a layer through which light cannot penetrate.

If the mulch particles are of a consistently large size, then a greater depth will be needed to prevent the light travelling through the gaps between the pieces. Smaller particles are better at fitting together to form a barrier, so 50mm may be adequate.

Topping up will depend on the type of mulch and its constituents, plus the prevailing conditions. In any case, it will be necessary to inspect the mulch 30 days after laying and top it up to compensate for settlement, a factor that can vary from five per cent for a good-quality bark mulch of uniform particle size to 20 per cent for mixed woodchips and composted green-waste mulches. The longevity of mulch will also depend on the type of material. Graded bark, such as Melcourt Industries' Nuggets and similar products from other firms, should be good for four or more years.

Topping up will be necessary to replace material dispersed by feet, wind or heavy rainfall. Where the mulch comprises a mixture of wood-fibre materials, and especially where there is a large range of particle sizes and some dust and fines content, then you are probably looking at replacement after two or perhaps three years. Composted materials give the shortest mulch life - sometimes as short as 12 months.

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