According to the National Gardening Association, garden soils can range from 5 to 9 on the pH scale. Often, gardeners must make adjustments to soil pH in order to grow certain kinds of plants successfully. Limestone, a naturally occurring component also referred to as calcium carbonate, is often used to raise the pH of soils, but there are other materials that can be alternatives for limestone in raising the alkalinity of garden soil.
Wood ash is often used as a low-cost alternative to limestone. It has been used as a soil amendment since the times of ancient Rome. When wood burns, the nitrogen and sulphur are expelled as gas and the calcium, potassium, magnesium and trace elements remain. These remaining components make good liming agents to raise pH in soil. Spread wood ash in the spring when soil is dry and before tilling, according to Emittsburg Frederick County Master Gardener. Wood ash can also be used to repel insects, slugs and snails. Wear eye protection, gloves and dust mask when working with wood ash.
Growers living in coastal communities have always used seaweed and other sea products to condition the soil in their gardens. Today, a number of processed seaweed products are available to gardeners. Some are in the form of calcified seaweed produced from beds of calcified and coralline algae. This is a good alternative to garden limestone and has additional trace elements and nutrients. According to the Royal Horticultural Society, it is generally more costly than garden lime.
Finely crushed oyster shells can be used as a good alternative to garden limestone. These are usually left over from the oyster processing industry. The shells are mostly calcium carbonate, the same component as garden lime, and are equally as effective, according to Clemson University. It also adds nutrients for the beneficial bacteria in soil.
Ordinary chicken egg shells are 95 per cent calcium carbonate, the same component as in garden lime, according to The Fertilizer Guide. They can be put into your compost pile or crushed finely and added directly to the soil. Or soak them in water in an airtight container for a few days and then add the water to the soil.
Blast Furnace Slag
Blast furnace slag, also called basic slag, is a by-product of the steel industry that is a calcium silicate material. Lime is used to remove impurities from molten iron ore, and the slag remains can be crushed and used as a soil amendment. It is used for liming in the agricultural industry.