Tips for gardening in acidic soil

October 9, 2015

To learn how plants that thrive in acid soil fit into their natural environment, explore a natural forest. The same forces that shape and nurture a forest create acid soil. As these tips will show, this is easily achieved by cultivating beds, working in ample compost to neutralize the pH, or by adding garden lime to over-acidic soil or adding garden sulphur to alkaline soil as directed on the package.

Tips for gardening in acidic soil

Indeed, acid soil is such welcome news to these and many other plants that if your soil is neutral to slightly acid, growing a woodland-type garden in acid soil requires little effort on your part. But not everyone wants a woodland in his or her yard. If you want to nurture colourful flowers and shrubs that aren't native to the woods, there's good news.

The vast majority of favourite garden plants, from petunias to roses, grow best in soil that is only slightly acidic or "near neutral", meaning that it has a pH between 6.2 and 6.8.

1. Limestone

Made from crushed limestone, lime is a very simple mineral soil amendment. The preferred type for most gardens, dolomitic limestone, enriches the soil with the plant nutrients calcium and magnesium while raising the soil pH.

Unlike most fertilizers, lime usually persists in the soil for several years, until repeated rains wash it away. It is seldom necessary to lime a bed more than once every three years or so, but the only way to know for sure is to test your soil's pH annually, preferably in the fall.

You can add lime to your soil in any season. Most gardeners lime in either spring or fall, when they are digging new beds or renovating old ones. Because lime dissolves slowly, it must be thoroughly mixed into the soil. Lime that is simply dusted onto the soil's surface takes months to benefit plants' deep roots. This is fine for lawn grass, and it may be your only option when adjusting the pH for roses and other well-established plants.

Dense, heavy clay soils require more lime than their light-textured, sandy counterparts, so there is no set application rate. However, a good starting point is 25 kilograms per 100 square metres (55 pounds per 1075 square feet). If you check your soil's pH before working in this amount and then recheck it six weeks later, you will have a good idea of how much change has resulted. If the soil is still very acidic, you can work in more lime the next time you dig the bed.

2. When handling limestone

  • Although lime is nothing more than finely pulverized rock powder, wear gloves when handling it, and avoid breathing the dust.
  • In its pure state, lime is sufficiently potent to dry your skin and irritate lung tissues.
  • Some stores sell lime in a granular (pelleted) form that is easier to handle.

3. Additional acidifiers

Garden sulphur, also known as wettable sulphur, is a fine powder consisting mostly of ground-up sulphur rock. It is used as a soil acidifier. Manure, peat moss, and acidic mulches like chopped oak leaves and pine needles will have a mildly acidifying effect on the soil.

The effects of these acidifiers are short-lived, so if your soil is alkaline, you should check the pH each season and add amendments as recommended by the test results.

Follow these guidelines to achieve a perfectly balanced environment for your garden.

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