Answer: The root system of your lilac vine should not be invasive enough to cause problems with leach lines or water lines. These plants do have a deep root system, as would other vines such as bougainvillea, but they are not considered invasive the way the roots of trees might be. I think you can safely plant your lilac vine in the garden. Over a period of years the roots will travel 3-4' out from the plant, and about 2' deep. Most utility and water lines are buried much deeper than that. Hope this information is helpful.
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