You have several choices when it comes to adding amendments to your garden beds. There are two ways to buy amendments: in bags or in bulk. Some things that you need in small quantities, such as pelletized fertilizer, can be bought by the bag; others, such as compost or soil conditioners, should be bought in bulk (Image 1).
Most garden centers sell a gardener's blend of composted manure, hardwood chips and humus, as well as a composted blend of plants and leaves (Image 2). Called soil conditioner, it has many of the elements garden soil needs. You can order it by the truckload and have it dumped out near your garden, then carry it in with a wheelbarrow as you need it.
This type of mixture has a lot to offer: The small chunks are recycled hardwood chips, and they'll provide structure and air pockets in the soil. The dark dirt around it is composted manure and humus; it will release a slow and steady supply of nutrients into the ground as it continues to break down. Because it's all composted, you don't have to worry about weed seeds and disease.