Sheet Mulch Bed

Sheet mulching makes a growing bed on ground already covered in lawn or weeds, without digging it up or spraying it. Plain cardboard or newspaper goes down first and shuts out the light, so the plants underneath die back where they stand. Layers of organic material go on top and rot down into the bed the crop will grow in.

The paper is laid over mown ground, tape and staples pulled off, nothing glossy, overlapped by 20 to 25 cm (8 to 10 in) so no seam is left open, and wetted as the work goes. Over it come alternating courses about 5 cm (2 in) deep, dry carbon-rich material such as straw or leaves and fresh nitrogen-rich material such as clippings or kitchen scraps, built up to between 45 and 90 cm (1.5 to 3 ft) and capped with 10 to 15 cm (4 to 6 in) of mulch. Then it waits: four to six months is usually enough, so the work is done in the cold season for planting in the warm one, and a vigorous warm-season grass underneath can stretch that to eight. Plant too early and the roots sit in undecayed material rather than soil.

The paper is also what goes wrong. On ground that drains badly it packs down wet into a sheet neither water nor air can cross, and the bed sours underneath; where it dries out it turns water-repellent, so rain runs off instead of soaking in. Neither shows from above, so the moisture beneath has to be checked rather than assumed. Cardboard attracts termites more than wood chips do and voles nest under sheets, so keep one away from a timber building. Running weeds such as bindweed or quackgrass find any seam and are better dug out first. It suits annual beds that somebody looks after, and is not recommended for permanent ornamental planting or ground nobody maintains. A covered soil takes raindrops without crusting, soaks in more rain, loses less to evaporation, swings less in temperature and fills with earthworms - but the cover rots down, so topping it up season after season is a separate, ongoing job.