When planting a garden bed with annual or perennial plants, you may want to consider buying or growing the plants in plugs. These plant starts grow in multi-cell trays, where each plant is in its own cell. This method of plant production allows the individual plants to develop compact, self-contained root systems that reduce the shock of transplant. Plug trays come in various sizes, holding anywhere from 6 to more than 50 starts. Plants in plugs fare best when acclimated to outdoor weather before being planted. Wait to plant until the last average spring frost date passes and soil temperatures warm to 70 degrees Fahrenheit.
Pull the tray of plugs out of its box or remove any wrappings covering the plants. Place the plants outdoors in full shade. Attach a sprayer nozzle to the end of a garden hose. Water the plugs with a gentle stream of water to thoroughly moisten their root balls.
Place the tray outdoors in full shade for two to three hours each day during the next two to three days. Water the plugs when the tops of their root balls feel dry. Gradually increase the amount of sunlight and outdoor time the plugs receive over the course of two weeks until they sit in full sun and stay outdoors around the clock. For plants that need shade, increase the amount of outdoor time only.
Pull weeds and remove rocks and debris from the planting site. Spread a 3- to 4-inch-deep layer of compost over the planting site with a rake. Mix the compost into the top 6 to 8 inches of soil with a rototiller or garden fork. Choose a site that gets the appropriate amount of sun or shade for the plants you've bought.
Spread a 5-10-5 nitrogen, phosphorous, potassium slow-release granular fertilizer over the planting site at a rate of 1 1/3 to 1 3/4 teaspoons per 1 square foot of soil. Mix the fertilizer into the top 3 to 4 inches of soil with the rake or garden fork. Smooth the soil's surface with the rake.
Dig one hole for each plug with a trowel. Make each individual hole twice as wide and equal in depth to the size of the plug's root balls. Base the spacing between each hole on the mature spread of the plants. For example, if the plant variety will grow to a width of 6 inches, then space the holes 6 inches apart. The label in the plug tray may give mature sizes.
Pinch the bottom of one cell in the plug tray gently to force the plug upward, out of the tray. Place the plug in the bottom center of a hole. Add or remove soil to the hole as needed to position the top of the root ball level with the encircling ground. Fill the hole with soil, tamping it firmly around the root ball. Do not overfill the hole or plant the plug deeper than it was previously growing. Repeat this process to plant each plug.
Water the planting site with 1/2 to 1 inch of water to moisten the soil to a depth of 6 to 12 inches. Use a hose with a spray attachment.