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updated: 9/23/2013 2:18 PM

Pine needles won't change soil acidity

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By Mary Boldan

Q. I have several blueberry bushes and heard that spreading pine needles around the base of the plants will increase the acidity of the soil.

A. Soil is typically acidic, neutral or alkaline. To have acidic soil, you need a pH lower than 7. You can find testing kits at most local gardening centers. For optimal success with blueberry bushes, the pH should be around 4.5 to 5.5. (The scale is measured from 0 to 14 with a pH of 7 being neutral. Above 7 is alkaline),

Once you know your pH you can determine if you need any additives to help obtain the level you desire.

Unfortunately, pine needles do not make the soil more acidic. Pine needles are acidic when they fall from the tree, ranging in pH from 3.2-3.8. If they are incorporated into the soil before decomposing they may have a very small effect on the soil's pH. However, if the needles are used as mulch on the soil surface, they have very little effect on plant growth because the roots are not growing in this material. As the needles break down, they are neutralized by the microorganisms that are doing the decomposing. So the bottom line; they are great as a mulch to keep soil cool, moist, etc., but don't really help in maintaining pH levels suitable for growing blueberries.

To make the soil more acidic, the home gardener must look at using garden sulfur at recommended amounts incorporated into the soil to drive the pH down before planting, and then maintain the pH by using ammonium sulfate at a rate of about 2 ounces per year per plant in the spring worked around each plant increasing the amount one ounce each year up to a total of 8 ounces as the plants get older.

While sphagnum peat moss is another good pH-lowering amendment is, it has fallen out of favor because it is a nonrenewable resource, and a vital element of peat bogs and wetland habitats.

• Master Gardener Answer Desk, located at Friendship Park Conservatory, 395 Algonquin, Des Plaines, is open 9 a.m. to noon on Wednesdays. Call (847) 298-3502 or email

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