There is much said of mulches so when selecting the the type you require there are a number of things to consider, for example;
Why use a mulch?
Mulches, of which there are many types, are generally applied on top of the soil to improve growing conditions, and in particular to reduce moisture loss from the soil, or to act as a weed suppressant.
They will also give some insulation to tender and/or shallow root systems, and create a habitat for various insects* and soil organisms*.
* This includes good and bad varieties!
What type should I use?
This can depend upon whether you are influenced by organic / inorganic gardening or financial restraints.
Here are a few suggestions; note they are in alphabetical order and not necessarily by preference.
Cost: Cheap organic mulches can decompose in one season, whereas a more expensive option could last up to three years.
Appearance may influences the choice. e.g.
A home-made woodchip mulch from a shredder may look attractive in the first season, but not so, after a short period of time, in contrast, weathered bark will retain its appearance much longer.
Organic mulches* that can be considered subject to availability are;
Chipped bark, Chopped bracken, Garden compost, Grass clippings, Green-manure, Farmyard manure, Leaf mould, Manure, Peat or Peat substitute, Spent mushroom compost°, Straw, Woodchips.
*Certain organic mulches will break down and provide some nutrients and improve soil structure.
° Should not be used around ericaceous plants.
In recent years various recycled materials such as Coloured glass, Crushed slate, Crushed stone, Horticultural fleece Pebbles, Polythene sheeting* Pulverized rubber / plastics are being used as an alternative to organic materials.
* Use black to suppress weeds, clear to warm up the ground.
If a non-biodegradable mulch is used, place a woven polypropylene layer under it.
Points against using mulch:
There is a greater risk of spreading pests and diseases.
Dependant on the type of mulch used, the amount of rainfall reaching the root systems can be affected.
Winter air is colder just above mulched ground than it is above bare soil.
A few simple rules when applying organic mulch around plants:
Late winter or early spring is an ideal time to apply mulch as this helps lock winter rain into the soil.
Do not mulch when soil is frozen.
Soak the ground prior to application, particularly to dry soil in dry weather.
Feed plants prior to mulching.
There after one will probably have to use a liquid fertilizer if feeding is required.
Apply mulches 75-100mm (3”-4”) deep.
Extend the layer as far as the drip-line (the whole area underneath the plant's branches)
Do not allow mulch to touch the trunks, stems or crowns of plants.
A thick layer of dense organic mulch can actually retard spring bulbs growth by keeping soil temperatures lower than bare soil therefore a thin layer of coarse mulch or no mulch at all tends to give better results.
With respect to weed suppression, although bark chips will successfully inhibit the emergence and establishment of annual weeds, it will have little impact on perennial weeds unless a permeable underlay has been laid below it.