Basic slag, a byproduct of iron smelting, can be used in place of limestone to raise soil pH, lowering the acidity level. Besides some native plants as well as azaleas, blueberries and gardenias, the majority of garden plants thrive best in only slightly acidic soils with a pH range of 6.0 to 7.0. Besides affecting pH, slag often contains calcium and magnesium, both essential nutrients for growing plants.
Contact your local agricultural extension office to obtain a soil testing kit. Follow the instructions provided with the kit and send the labeled soil back to the extension for analysis. Your results will be returned, including the current pH balance and how much limestone to add to raise the pH.
Fill a drop spreader with the recommended amount of powdered slag and distribute it throughout your garden. For a small garden, you can distribute the slag by hand.
Break up the soil, using the rototiller or garden spade to work the slag 6 inches into the soil.
Retest your soil before planting seeds to ensure the pH is in range.