Hardwood mulch, like the Jemasco brand, is chipped hardwood from branches and trees, and from other natural materials such as sawdust or clippings. Once it has broken down, hardwood mulch becomes alkaline. Hardwood mulch benefits plants except for those that need acidic soil. Because hardwood mulch creates alkalinity, you should consider using this type of mulch around your alkaline-loving plants. These include hawthorn, forsythia, and hydrangea.