Answer: Leaves can turn purple because of cold weather, or low phosphorous in your soil. Your soil test should also tell you the soil's pH. This is important to know because soil that is too acidic or too alkaline can bind up nutrients and make them unavailable to plant roots. Star jasmine will grow best in slightly acidic soils. If your soil is very alkaline, any phosphorus in your soil won't be available to the roots of your jasmine even though a soil test shows adequate amount in your soil. I would try to work some peat moss or compost into the soil near the roots of the jasmine (without damaging the roots), then mulch over the root system with pine needles or compost. This should provide enough acidity to help the roots of your plants take in the phosphorus they need. Feed with an acidified fertilizer, as well. Miracid or Miracle Gro will provide the needed nitrogen along with additional nutrients. Hope this helps!
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