May is a good time to plant vegetables in many parts of the country. In the northern parts of the United States, soil temperatures do not warm enough to place transplants and seedlings into the ground until early May. In southern parts of the country, crops that are planted in succession such as beans can be planted throughout May. You can consult the tags on transplants as well as the backs of seed packets to determine what plants should be planted in May for your area.
Start seeds indoors in early March for transplanting outdoors during May. Place seeds in seedling trays filled with slightly damp peat moss and cover with plastic. Put the trays under a grow light. Remove the plastic when the seeds germinate. Move the trays outdoors in the shade during daylight hours to harden them off for transplanting in May.
Prepare your garden bed by breaking up the soil to a depth of 12 inches with a rototiller in late April after the ground has dried. Never try to break up soil when the ground is saturated with water. This can cause the soil to compact. Spread a 4-inch-thick layer of organic material such as peat moss, compost and composted manure over the top of the bed. Mix the amendments with the soil using the rototiller.
Open a planting hole for transplants and seedlings with a shovel. The planting hole should be twice as wide as the transplant's root ball, but no deeper. Place the root ball of the seedlings or the transplants into the hole and cover with soil.
Create furrows or drill holes for seeds in the soil of your garden with a rake and your fingers. Place the seedlings into the furrows or drill holes so they are planted twice as deep as the seed's widest point. Cover the seed with soil and water so the soil is as damp as a wrung-out sponge.
Cover the area around transplants and sprouted seeds with seedless straw mulch to a depth of 4 inches to crowd out weeds and hold moisture in the soil.