A mulch layer can help to conserve soil moisture and reduce weed growth; this can diminish or even eliminate the need for cultivation during the growing season.

Mulches fall into two categories - organic types that decompose naturally in the soil, and inorganic types that do not decompose and therefore must be removed after serving their purpose. The choice between an organic or an inorganic mulch usually depends on the primary reason for the mulch: organic mulches conserve moisture, improve soil structure and add nutrients, whilst inorganic mulches are excellent for raising the soil temperature and suppressing weeds.

Organic Mulches

Organic mulches include compost, well-rotted manure, dried lawn clippings and peat moss. Wood-based materials such as sawdust, newspapers, bark chips and wood shavings may also be used; however, these should be allowed to rot down for at least 2 years prior to using, as their decomposition uses up soil nitrogen.

Apply a thick layer (2-7 cm or 1-3 in) of organic mulch in the spring or early summer, when the soil is reasonably moist and has had a chance to warm up. Although it is usually easer to apply this layer when planting, it can also be added around established plants, as long as they are at least 7 cm (3 in) high. Deeper layers of mulch are more effective at suppressing weeds than shallow ones.

Inorganic Mulches

Inorganic mulches such as plastic (clear, white or black) may be applied to raise soil temperatures, suppress weeds, reflect heat up to ripening fruit or deter flying pests.

• Black: Suppresses weeds and raises soil temperature approximately 3°C (5°F).
• White: Reflects light and heat up on to ripening fruit, raises soil temperature approximately 5°C (10°F).
• Clear: Raises soil temperature by approximately 5°C (10°F) and keeps vegetables clean by preventing soil splash.

Inorganic plastic films are easier to apply before planting. Cover the vegetable plot with a layer of sheeting, making sure that any required seep systems have been installed. The edges of the plastic should then be buried in 7-10 cm (3-4 in) deep trenches to prevent the wind from blowing it away. Short slits are then made in the material with a knife for depositing seeds or planting transplants. When seedlings appear, guide them through the holes so that they do not become trapped.