Most gardeners strive to achieve a neutral pH level in their edible and landscape gardens. But in some cases you'll want to bring the pH level lower than the neutral range of 6.5 to 7.5. In general, lovers of acidic soils--including blueberries, pines, rhododendrons and laurels--prefer a pH level between 4.0 and 5.5. Several organic methods of creating acidic soil exist.
Apply Sulfur
Bags of powdered elemental sulfur are widely available at garden centers. A soil test conducted by your local extension service may provide you with the recommended amounts to add to your soil. "Rodale's Ultimate Encyclopedia of Organic Gardening" notes that the average recommendations call for adding one pound of sulfur per 100 square feet for every pH level point you need to lower. In other words, if you have alkaline soil that registers at 7.0 and you want to achieve an acid soil of about 5.0, till about 2 pounds of sulfur into every 100 square feet of soil.
Add Peat Moss
Sphagnum peat moss, while more expensive and bulky than other amendments, works well in small patches of garden which require acid soil. In most cases, you'll add one to two inches of dry peat moss on top of the soil, wet it with a hose, and work it in to the recommended depth. Increase the application as needed. Iowa State University recommends you add no more than two pounds of peat moss per 100 square foot of garden; too much sulfur can damage plants.
Dig in Acidic Compost
Set aside an area to compost one or more acidic, organic materials. Rotted leaves, sawdust, manure and pine needles are all acidic. Work the aged compost into the ground several months before planting to give it time to further decompose. The effects this material will have on your soil are harder to calculate than with bagged materials. So conduct a soil test prior to planting, and determine if the soil needs further amending.
Mulch with Pine Needles
Pine needles add acididity when used as mulch. Spread the needles several inches thick after establishing your acid-loving perennials or shrubs. As the mulch decomposes, it helps maintain the lowered pH level. Add fresh pine needles every year or two.
Avoid Alkalizers
Some gardeners add wood ash or ground limestone to their soil for the trace minerals, including calcium and magnesium, which they contribute to the soil. But both wood ash and limestone raise the pH level of the soil---an effect you don't want when creating an acidic garden plot . And while adding dishwater or using a gray-water system is a smart conservation method in most cases, be aware that it makes soils more alkaline.
References
- "Rodale's Ultimate Encyclopedia of Organic Gardening"; Fern Marshall Bradely, et al; 2009
- Iowa State University: How to Change Your Soil's pH
- New Mexico State University: Safe Use of Household Greywater
