Tofino gardening: Why Lime?
by Sarah Sloman
For a gardener spring is a great time of the year. the bulbs are blooming and the air starts to smell like fresh cut grass, but what is that white stuff on that lawn and why is it there?Well, it is lime and lime will greatly affect the pH of your soil. If you would like to use lime we should clarify to use dolomite lime only. Dolomite lime comes prilled or powdered and is always chalk full of calcium carbonate and magnesium carbonate, plants find both delicious. For application the powdered dolomite lime is quite affordable and a bit hard to spread, the prilled dolomite lime is more costly, but spreads like a dream, both raise the pH of the soil.
PH is the number of hydrogen ions in the soil. Soils with a low pH are acidic and soils with a high pH are alkaline; most plants prefer a pH of 6.0 - 6.5. The pH of the soil can be a result of parent rock in the soil, the use of acidifying fertilisers, some of our locally available mulches or rainfall. So if you have a limestone your back yard you probably don’t need to lime but for the rest of us we all need to and we may need a lot depending on your soil type.
Sandy soils leach very quickly in our weather, but they are easily affected by fertilisers very rapidly so they require light amounts of lime and often. The pH of clay soils doesn’t change very easily but once it is changed it is not so quick to switch back so therefore these types of soil require large doses of lime and not too often (2 times a year). Lime is really important in clay soils because it can improve the soil structure which will result in better aeration and drainage.
PH greatly affects the amount of nutrients available to your plants. A correct pH can release up to 90% more nitrogen to the soil. Altering the pH up and down will temporarily make phosphorus available; this is very important because phosphorus is so tightly locked up in the soil it is hard to make it available to the plants we love so much. Some plants prefer a more acidic soil than others Rhodos thrive in acidic soils because more iron is available, so don’t lime them too much if at all. Horsetail prefers an acidic soil so if you have a horsetail infestation you may want to try liming. Worms do not like acidic soil and we would all love to for the red wrigglers to be happy. Soil tests are available to determine the pH of your soil if you are in doubt. If you have moss in your lawn, this is usually a result of the soil being to acidic.
Sarah Sloman is a trained horticulturist and owns and operates Pacific Earthworks in Tofino.
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