Peat Usually makes the soil more acid. It is quite costly unless dug locally, and these days is generally frowned on because of the environmental impact of peat harvesting on wildlife habitats. It does not contain many weed seeds, and the coarse grades are best for soil composition improvement. If well made, this is a very useful material, but is generally weaker at soil improvement than peat or manure. It does not supply much plant food and can contain weeds and some diseases if not properly made.
Regular use is needed fore the best effect.
This is one of the few types of organic matter to have a slightly alkaline effect on the soil. It is therefore good for soils that need both composition improvement and raising of the pH level, or soils at the right pH level that would become too acid if peat or manure were to be used. It makes an ideal mulch, although it can be dug in at any time. If you plan to use straw, try to rot it down first, or at least add some extra nitrogen to compensate plants for the loss. Leafmould The value of this depends on the sort of leaves that have been used to make it.