While soil that is fairly pH-neutral is good in many cases, certain types of plants require acidic soil to thrive. If you have soil that is not acidic enough for your favorite fruits or flowers, it’s possible to make it more acidic by adding various natural ingredients. By doing so, you can affect the pH over a large patch of soil or just around a single plant.
Add Some Vinegar
Vinegar is a mild acid, and adding it to the soil will increase the soil’s acidity. The pH will drop one to two points, depending on how large of an area you water and what type of soil you have. Typically, the effects don't last longer than 48 hours. If you water the area with plain water or if it rains, the effects may not even last that long, but don't use vinegar every day; once or twice a week may be enough.
Stir 1 cup of vinegar into each gallon of water that you use to water your plants.
Place the mixture in a watering can.
Pour the vinegar and water around the roots under the plant.
Mix in Some Sphagnum Peat Moss
Sphagnum peat moss is acidic, so it will lower your soil’s pH and help to keep it low over a period of about two years. Peat will also help lighten heavy soil and add organic matter to the soil. Before planting, spread 1 to 2 inches of peat moss over the area of soil that needs its pH lowered. Next, use a shovel or a tiller to work the sphagnum peat into the soil’s upper 8 to 12 inches. This method is best for relatively small areas, as using sphagnum peat moss on a large yard or garden would be extremely expensive. It takes 2.5 pounds of peat moss to lower the pH of 1 square yard of soil by one point, so you'd need about 85 pounds to lower the pH of a garden 10 by 30 feet by a point.
Incorporate Elemental Sulfur
Add elemental sulfur, a naturally occurring element often found near volcanoes, to your soil for a long-lasting drop in pH. Exactly how much you add will depend on your soil’s current pH and the level that you desire. To drop the level of sandy soil one full point, add 1 to 2 pounds of elemental sulfur to each 50 cubic feet -- that’s an area 10 feet by 10 feet by 6 inches deep. If you have loam instead of sandy soil, use from 3 to 6 pounds of elemental sulfur for the same area, and for clay soils use 4.5 to 9 pounds for the same area. This is a project you need to do well in advance of planting because elemental sulfur takes about a year to reduce soil’s pH.