Pin oak (Quercus palustris) is an attractive landscape tree, but it can look bad when grown in the wrong spot. It sounds as if this is what is happening to yours. Pin oak likes well-drained, slightly acidic soil. If your landscape soil has too high a pH, your tree can't absorb the nutrients (iron in particular) that it needs from the soil, and as a result it develops pale leaves. Typical symptoms of iron chlorosis are yellowed leaves with green veins. A spray of chelated iron, available at garden centers, may green up the foliage. But a long-term fix will require more work. Start with a soil test. If your soil is too alkaline, use elemental sulfur, iron sulfate, or another soil acidifier to lower the pH. Keep the tree watered well during times of drought, and mulch the soil around the tree with compost or bark chips. Fertilizing the tree in spring or early summer can help too.