|What would be a good soil mix to fill raised beds that will be used for planting vegetables?|
|Usually it is best to start with the native soil and add organic matter to it such as compost, old rotted down leaves, well aged stable manure and bedding, and so on. If your soil is clayish you might also add a small amount of grit or coarse sand. This process will raise the soil level somewhat.
Additional amendments such as fertilizer would be added, if needed, based on basic soil tests. Your county extension should be able to help you with the tests and interpreting the results.
You will find that simply loosening and fluffing the soil raises its level somewhat, and the addition of ample amounts of organic matter will also help raise it. Each year you will need to add more humus to help maintain and increase the bulk. Using an organic mulch will also help improve the soil structure and feed it as it breaks down.
Keep in mind that soil building is an ongoing process and the beds do not need to be raised terribly high to provide good results since many vegetables are not so deep rooted. If you are simply trying to improve drainage, for instance, several inches can be enough. Over time your efforts will show cumulative results and the soil will be well improved.