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Why the pH of Your Garden Matters

September 19th, 2011 Gardening

You may think all you need for a successful flower or vegetable garden is soil, seeds, fertilizer and water. While those are essential ingredients, many gardeners fail to consider the pH level of their soil, which can have a huge impact on whether or not the plants thrive.

pH basics A substance's pH is a measurement of its alkalinity or acidity. These two qualities depend on the concentration of hydrogen irons. The more hydrogen ions a material has, the more acidic it is. The pH scale goes from 0 to 14, where a neutral substance is measured at 7.0. Anything below 7.0 is considered acidic, while anything above is considered alkaline, or basic. Every point on the pH scale has 10 times more hydrogen ions than the number below it.

To get an idea of how it works, consider the pH measurements of several common liquids. Lemon juice, which is very acidic, has a measurement of 2.0. Orange juice is still acidic, but not as much, with a measurement of 4.0. Blood is pretty neutral, but slightly more basic than acidic, at 7.3. The common household cleaner, ammonia, is very basic, measuring 11.0.

pH in the garden Most plants have the most success in slightly acidic soil, around 6.5 on the pH scale. However, some plants thrive in more basic soil. If the soil is too acidic or too alkaline for your plants, they won't be able to absorb the nutrients they need to grow strong. Roots can only absorb nutrients like nitrogen and iron when they're dissolved in water, and if the solution isn't the right pH, they won't be able to access the nutrients.

Environmental factors can affect pH levels. You can't determine the pH of your soil without testing it, but there are a few general rules that usually apply. For example, areas with a lot of rain and dense forests have more acidic soils than those with light rainfall and prairies.

Common plant preferences Here's a list of common plants and their preferred pH levels, according to West Virginia University.

5.25 - 6.0 pH Potatoes, strawberries, sage, blackberries, rosemary and pineapples all thrive in an acidic environment.

6.0 - 6.75 pH Baby's breath, daffodils, sunflowers, pear trees, rose bushes, squash, carrots, lentils, and watermelon prefer less acidic soil.

6.75 - 7.5 pH Avocados, mushrooms, asparagus, honeysuckle, wisteria, hyacinths and forget-me-nots grow best in a relatively neutral garden.

How to manage pH levels If you're planting a garden that requires multiple pH levels, it makes sense to group together the species that require the same type of soil. To adjust the pH levels of your garden, you need to test its current level, which you can do with a kit that can be bought at most gardening supply stores.

Once you've evaluated the pH, decide if you need to raise or lower the pH level. If your soil is too acidic, you can add ground limestone to your garden. Apply it in the fall to give it time to process before the next growing season. Wood ashes also work to raise the pH. To lower pH, add acidic compost to your garden. Use materials like pine needles, sulfur, sawdust and peat moss as mulch to keep the soil acidic in the long term. Your plants will flourish once they're growing in the proper environment.