The editors of Sunset magazine sent a batch of used coffee grounds to a laboratory for analysis and found out that it makes an excellent soil conditioner and will act as a slow-release fertilizer if added in sufficient quantities. Whether you decide to mix your used coffee grounds into the planting bed or into the compost pile, your plants will get a nice jolt of phosphorus, potassium, magnesium and copper. As a bonus, the grounds act as feed for earthworms, so they'll be attracted to the garden in larger numbers.
Dig into the planting area to a depth of 12 inches, using the gardening fork. As you dig up the soil, turn it over and crush any large clumps. Remove any rocks and other debris that turns up.
Add the coffee grounds to the soil. According to the Soil and Plant Laboratory analysis used by Sunset, the planting area should contain 35 percent coffee grounds.
Till the grounds into the soil to a depth of 8 inches. Level the planting area and water well. Your garden is now ready to be planted.