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Leaves can be used as mulchThe pH of soil is a measurement of how acidic or alkaline it is. Anything below a pH measurement of 7.0 is classified as acidic. Anything higher than 7.0 is classified as alkaline. Soil pH is important because nitrogen, which is an essential nutrient, is not manufactured in soil with a pH above 5.5. Phosphorous, on the other hand, needs a pH in the 6.0-7.0 range. In addition to nutrients, plants, shrubs and trees often require a certain pH range in order to grow or thrive. - The leaves of some trees, including beech, oak and pine needles, fall in the 4.3 to 5.5 pH range, making them highly acidic. However, that acidity lessens as the leaves decompose, leaving a fully-decomposed mulch with a pH of about 6.5, which is almost neutral and is beneficial to many flower and vegetable species, such as dahlia, dianthus, gladiola and lilac, which need a pH between 6.0 and 7.5.
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Oak leaves are acidicIf the soil is too alkaline, most plants will not survive. Though a few plants thrive in alkaline soil--salt grasses can survive in a pH of 8.0--most prefer a pH in the middle range of the scale, since more soil nutrients are found in soils with pH values nearer the middle. As a result, leaf mulch benefits all but the most alkaline-soil loving plants. - Some trees need acidic soil, but since leaf mulch does not have much effect on soil pH, additional soil additives will be needed. Mulching with sphagnum moss will add needed acid as it slowly decomposes. In addition, mulch that contains partially decomposed leaves from trees listed in Section 2 is more acidic than its fully decomposed counterpart.
- While mulch made from fully decomposed leaves has little effect on soil pH, it does ease soil erosion, maintain soil moisture and temperature, inhibit weed growth and improve the nutrients in the soil.
