What sort of soil mixture should I fill my raised bed with?

The experts vary on their advice a little here.

Mike McGrath of NPR’s You Bet Your Garden says to fill you beds with 50% compost and 50% screened topsoil.

Mel Bartholemew of Square Foot Gardening says to use an even mixture of 1/3 peat moss, 1/3 coarse horticultural vermiculite and 1/3 blended compost (from at least 5 different compost sources for a variety of ingredients).  So no topsoil at all in his mix.  Proportions are measured by volume, and the peat moss volume is uncompressed (so a 3 cubic feet bale is actually 6 cubic feet when broken up for Mel’s Mix).

To save money, you might choose to try lasagna gardening – fill your bed mostly with a mix of organic compostable material (shredded leaves and grass clippings would be ideal), cover with several layers of newspaper or cardboard and top off with only 6 to 12 inches of your preferred soil mixture to plant into.  Long-rooted crops may need a deeper soil mix, but for many garden crops 6 to 12 inches is enough.


What are the advantages of gardening in raised beds over traditional row gardens?

  1. you can grow twice as much or more produce in the same space, so if you have limited space a raised bed garden may be the only way to produce what you need
  2. because you can grow more, raised beds help you save more money (once your investment in the raised beds is repaid) by growing your own organic produce
  3. you never have to till the soil (because it is never compressed), which not only saves you work but the no-till method is also better for your soil
  4. an array of raised beds can be much more visually appealing in your yard than a conventional row garden
  5. by raising the level of the soil closer to your hands, you don’t have to bend down as much to do garden chores (saving your back and making gardening much more enjoyable!)
  6. you can space plants much more densely inside of a raised bed (because you don’t have to leave space for rows to walk in), which shades more ground and thus cuts down on weed germination and growth
  7. you can focus your resources (water and fertilizer) more inside of a raised bed than in a conventional row garden (which tends to get water and fertilizer over the whole area – including the walking rows where it is mostly wasted)
  8. raised beds (especially if they are tall) can help protect your growing areas from pets, children and some garden pests (and also weed seed blown about by the wind)
  9. if you are concerned about the safety/toxicity of your native soil (if you are in an urban environment then you probably should be), raised beds allow you to grow in a safe, organic soil mixture of your choosing
  10. growing organically is easier in raised beds (because of the premium, un-compressed, organic soil mixture – which makes plants stronger and thus less susceptible to disease and insects)
  11. you will have greater access to your raised beds than you would in a conventional row garden (when soil is wet and muddy, you should stay out of a conventional garden until it dries – not so with a raised bed garden where the paths can be walked on at all times)


How do raised beds achieve such dramatic out-production vs conventional row gardens?

  1. you never compress the soil by walking on it inside a raised bed, which keeps your soil loose and airy
  2. you can fill your raised bed with a premium soil mixture (this benefit is greater the poorer your native soil is) tailored to your individual gardening situation (if you live in a very rainy climate you can make the mix more drainable and vice-versa for dry climates)
  3. you can extend the growing seasons by simply raising the level of the soil off of the ground level (which is where cold air pools)
  4. you can plant more densely (which also suppresses weeds – less weeds means less competition for nutrients and water)


What are some of the best organic soil amendments for a raised bed?

  1. compost (from multiple sources if possible – including homemade by you – to create a blend with varying characteristics)
  2. worm castings (the best soil amendment of all – make your own by starting a worm bin)
  3. greensand (a slow-release source of potassium and also micronutrients)
  4. bat guano
  5. kelp meal