Swiss chard grows best in rich, moist soil with a soil pH between 6.0 and 6.8. Plant in fertile soil because plants should grow fast to produce tender leaves. Work nitrogen-rich amendments such as blood meal, cottonseed meal, feather meal, or composted manure into the ground before planting. Or, apply a timed-release vegetable food such as 14-14-14 according to label directions. Swiss chard does best with a nice, even supply of water. Water regularly, applying 1 to 1.5 inches of water per week if it doesn't rain. You can measure the amount of water with a rain gauge in the garden. Apply organic mulch such as compost to keep the soil cool and moist and to keep down weeds. Mulching will also help keep the leaves clean.
Do water regularly, especially in summer, as drought-stressed plants may bolt, or flower.