Best Soil for Raised Bed Vegetable Gardening

If you’re wondering what the best soil for raised bed vegetable gardening is, that’s an easy answer – “Mel’s Mix”. I didn’t come up with this mix; we can thank Mel Bartholomew, the author of Square Foot Gardening, for simplifying the best soil to use for raised bed vegetable gardening.

After reading Square Foot Gardening for the first time over 12 years ago, I decided to start my own garden. I followed the advice for how to make Mel’s Mix, which he calls “the most important, productive, essential, necessary, critical” ingredient for square-foot gardening success, and it worked!

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The Best Soil for Raised Bed Vegetable Gardening is Mel’s Mix

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What is in Mel’s Mix?

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Regular garden soil is too dense for raised bed gardens. Mel’s Mix for square-foot gardening mixes compost, coco coir, and vermiculite, which keeps the soil light and airy.

Mel Bartholomew’s mix for the best soil for raised bed vegetable gardening is simple:

• 1 part compost – Make your own, or If you live in Arizona, the compost from Arizona Worm Farm is great. If you use bagged, a mix of several different types is best.
• 1 part  coco coir
• 1 part vermiculite or perlite
• 3-5% worm castings (1/3 gallon per cubic foot)
• 1/2 cup basalt dust per cubic foot

Measure each type by volume (cubic feet), not weight.

You can also use up to 50 percent compost to 25 percent each of vermiculite and coco coir.

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Great news for Phoenix-area residents

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Fall 2020  Arizona Worm Farm (located in Phoenix, Arizona) began selling “Growing in the Garden Raised Bed Mix” that is premixed and ready to go! It is available by the bag or by the yard and also available for delivery. It contains the correct mixture of compost, coco coir, vermiculite, worm castings, and basalt dust.

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What are the advantages of using this mix for raised bed vegetable gardening?

The benefits of using this soil mix for raised bed vegetable gardening include:

• It simplifies drainage – the vermiculite and coco coir absorb moisture; when they are saturated, excess moisture drains away. This means you can’t overwater.
• Seeds germinate easily in the mix.
• No weeds! It really is true. In the years I’ve been gardening, I rarely see a weed inside the raised beds. The soil remains light and airy; it does not get crusted or compacted. Plants’ roots need oxygen and water, and roots love this mixture.

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Adding a balanced organic fertilizer before you plant to your soil mixture for raised beds helps give plants the food they need to grow and thrive in your garden. You are feeding the soil that feeds your plants.

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What’s the best way to combine the ingredients in the raised bed mix?

One way to mix up the ingredients for the best soil for raised bed gardening is to combine the ingredients in batches on a tarp. Once they are combined, contents can be dumped into the raised bed. Once you fill your bed, water the soil very well.

You can also layer the ingredients (lasagna style) in the raised bed, mixing well after each addition.Make up a little extra raised bed mix to use in pots and containers

This raised bed mixture also is a perfect potting soil, so I like to mix up extra of this soil mixture and store it in a large-lidded garbage can. It’s very convenient to have the mix on hand for filling pots and for other areas in the garden.

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Add more compost to raised beds each time you plant

At the end of the season, as the soil level goes down from the decomposition of the compost, add additional compost to bring the soil level back up to the top of the bed. It isn’t necessary to add additional coco coir and vermiculite to your beds each season, as the coconut coir and vermiculite do not break down as quickly. The continued practice of adding compost and feeding your soil each season improves the soil and the harvests.

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Test your soil once a year

About once a year after adding soil to your raised beds, it’s important to have your soil tested. A soil test can determine the health of your soil. This is the soil test kit I use. It’s simple to use. 

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