Managing your soil's pH in San Diego can be difficult. A pH of 6.0 to 7.2 is optimal for the growth of most garden and landscape plants. However, soil pH in the range of 7 to 8 is adequate for many plants, especially those adapted to arid, Western U.S. environments. Living with slightly alkaline soil (pH 7.0-8.0) may be easier and less expensive than trying to lower soil pH. Selecting plants that tolerate high soil pH conditions will insure success in plantings and few problems with iron or other nutrient deficiencies. Source: Utah State Cooperative Extension
If soil pH is above 8.0 (or you don't want to change your plant selection) consider the following measures to lower the pH of alkaline soils:
Amend the soil with organic matter. On average, soils with higher organic matter contents have lower pH. Pet or sphagnum peat moss are highly acidic and will lower soil pH more than other organic amendments.
To safely acidify soil where you already have plants applying elemental sulfur is the best way. Sulfur is very slow acting (it may take as long as 3-4 months to be effective). Applied at recommended rates, it’s safe for your plants.
Iron sulfate is good, too. Iron sulfate acts more quickly (it takes about 2-3 weeks to affect the pH) but it takes a lot more of the chemical compared to using elemental sulfur. Be especially careful with iron sulfate. It will leave rusty stains on your clothes, sidewalks and patios. It’s even a good idea to wash your gardening clothes separately from your other laundry after spreading iron sulfate. Source: Bachmans.com
