Answer: Pine needles are commonly used as mulch without any problems that I'm aware of. They are acidic, and sometimes gardeners with acidic soil worry that the pine needles will make the soil more acidic. However, pine needles do not break down fast enough to change the soil's pH in a year. Before it rots, organic matter of any type will have little effect on soil acidity. "Last year I mulched my blueberries with a four inch layer of fresh and partially decomposed pine needles, and after a year the pH hadn't changed at all," said Eric Evans, lab director of the Woods End Soil Laboratory in Mount Vernon, Maine.
As for using them in place of straw, you might need to use a thicker layer because pine needles are "lighter and airier" but they still make a good protection. Pine needles are what Mother Nature uses on the forest floor--she doesn't have easy access to bales of straw! I hope this info helps.
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