Question #2: What is the best raised bed soil mix?

December 4, 2009

Here ya go Ann!

I get lots of questions on what to use to make the best soil mix for raised beds. Now, I'm sure there are a million good recipes out there, but I'll give you a some quick suggestions of what I use that works well for me.

Remember that brand "new" soil mixes are often not that fertile at the get go. They take a little time to start to break down and for the population of beneficial microbes to grow. Initially, plants in new soil may often look yellow or stunted. Feed the soil by adding things like dry molasses, dry seaweed or liquid bio-stimulants. You must make sure to mix in fertilizer with the soil and planting and provide supplemental fertilizer.

(Ann, specifically on the Letco bedding mix, I would not use that mix for veggie beds. They have a better bulk mix called Specialty Planting Mix (and now a Vegetable planting mix 2012). I've used that mix in about 5 of my veggie beds and it's working pretty well. It's still less than a year old, and so initial fertility was not high, but it's getting better.)

If you're buying bagged soil and making your own mix, here is what I often recommend. I'll use a 4' x 4' bed that is 12" high for the example. First you want to get your volume. Remember that 1 cubic yard equals 27 cubic feet. And to get your bed volume multiply the width, length and height in feet.

4 x4 x 1 = 16 cubic feet. That's how many cubic feet of soil your bed will need. If you're buying 2 cubic foot bags then the bed will take 8 bags, if you're buying 1 cubic foot bags, it will take about 16.

For this bed you could use (each of these are 1 cu. ft. bags)

  • 6 bags of a high quality topsoil such as Soil Menders Enriched Topsoil(NOT builders trash topsoil)
  • 6 bags high quality compost (I like Vital Earth)
  • 3 bags of Humus, such as Soil Menders Plant and Soil Food
  • 1 bag of Composted cow manure

Then you're going to need to amend that mixture with your granular vegetable fertilizer and you can also add things like dry molasses, dry seaweed, greensand and lava sand. Expanded shale can be added to mixes for beds that need improved drainage. If you plan on growing root crops such as carrots in the bed, skip the expanded shale or any other chunky product. 

If you're buying a bulk soil, look for one that has a good mix of compost, topsoil (quality), some finely shredded landscapers mix (not chunky), humus and amendments like greensand.

This is super quick...and I'm headed out of town, but I hope this helps!

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