Mulch

Towards the beginning of the growing season, mulches serve initially to warm the soil by helping it retain heat which is otherwise lost during the night.

As the season progresses, mulch stabilizes the soil temperature and moisture, and prevents the growing of weeds from seeds.

Use takes into consideration availability, cost, appearance, the effect it has on the soil—including chemical reactions and pH, durability, combustibility, rate of decomposition, how clean it is—some can contain weed seeds or plant pathogens.

In these areas, the word "mulch" is used specifically to refer to very fine tanbark or peat moss.

Some mulches such as straw, peat, sawdust and other wood products may for a while negatively affect plant growth because of their wide carbon to nitrogen ratio,[18] because bacteria and fungi that decompose the materials remove nitrogen from the surrounding soil for growth.

[19] Organic mulches can mat down, forming a barrier that blocks water and air flow between the soil and the atmosphere.

Commonly available organic mulches include:[9]: 768–772 Leaves from deciduous trees, which drop their foliage in the autumn/fall.

Thick layers of entire leaves, especially of maples and oaks, can form a soggy mat in winter and spring which can impede the new growth of lawn grass and other plants.

Grass clippings are dense and tend to mat down, so are mixed with tree leaves or rough compost to provide aeration and to facilitate their decomposition without smelly putrefaction.

Grass clippings are often dried thoroughly before application, which militates against rapid decomposition and excessive heat generation.

Fresh green grass clippings are relatively high in nitrate content, and when used as a mulch, much of the nitrate is returned to the soil, conversely the routine removal of grass clippings from the lawn results in nitrogen deficiency for the lawn.

It can also lower the pH of the soil surface, making it useful as a mulch under acid loving plants.

However, peat bogs are a valuable wildlife habitat, and peat is also one of the largest stores of carbon (in Britain, out of a total estimated 9952 million tonnes of carbon in British vegetation and soils, 6948 million tonnes carbon are estimated to be in Scottish, mostly peatland, soils[21]) Wood chips are a byproduct of the pruning of trees by arborists, utilities and parks; they are used to dispose of bulky waste.

Tree branches and large stems are rather coarse after chipping and tend to be used as a mulch at least three inches thick.

Woodchip mulch is a byproduct of reprocessing used (untreated) timber (usually packaging pallets), to dispose of wood waste.

The finer types are very attractive but have a large exposed surface area that leads to quicker decay.

Layers two or three inches deep are usually used, bark is relativity inert and its decay does not demand soil nitrates.

On application pine needles tend to weave together, a characteristic that helps the mulch hold stormwater on steeper slopes.

This interlocking tendency combined with a resistance to floating gives it further advantages in maintaining cover and preventing soil erosion.

[28] Ultimately this can reduce the amount of herbicides used and manual labor farmers may have to do throughout the growing season.

Microorganisms in the soil break down the mulch into two components, water and carbon dioxide, leaving no toxic residues behind.

[27] This source of mulch requires less manual labor since it does not need to be removed at the end of the season and can actually be tilled into the soil.

This is usually part of a sophisticated mechanical process, where raised beds are formed, plastic is rolled out on top, and seedlings are transplanted through it.

The black and clear mulches capture sunlight and warm the soil increasing the growth rate.

When colored mulch first entered the market, most formulas were suspected to contain toxic substances, heavy metals and other contaminates.

Today, "current investigations indicate that mulch colorants pose no threat to people, pets or the environment.

[39] Groundcovers are plants which grow close to the ground, under the main crop, to slow the development of weeds and provide other benefits of mulch.

However, live mulches also may need to be mechanically or chemically killed eventually to prevent competition with the main crop.