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Choosing the Best Soil for Raised Bed Gardening

Gardening in raised beds is a fantastic way to grow vegetables, offering better drainage, easier access, and complete control over the soil you use. One of the critical factors in ensuring a productive garden is selecting the best soil for your raised beds. Whether you’re a beginner or an experienced gardener, the right soil can make all the difference. In this post, we’ll explore the properties of good raised bed soil, how to create the perfect mix, and why Mel’s Mix—a soil blend from the creator of Square Foot Gardening—is a game changer for raised bed vegetable gardening.

Article Outline:

• Why Soil Quality is Essential for Raised Beds
• The Best Soil for Raised Bed Vegetable Gardening is Mel’s Mix
• What is in Mel’s Mix?
• Arizona Worm Farm Raised Bed Mix
• Advantages of Using Mel’s Mix for Raised Bed Vegetable Gardening
• How to Combine the Ingredients for Mel’s Mix
• Maintaining Your Raised Bed Soil

Why Soil Quality is Essential for Raised Beds

Raised beds offer numerous advantages, but success depends mainly on the soil quality you use. Here’s why soil quality is so important:

• Better Drainage: Good raised bed soil improves drainage while ensuring that plants still get the needed moisture.
• Root Growth: Loamy, well-aerated soil encourages roots to spread and access nutrients.
• Nutrient Availability: Nutrient-rich soil is vital for healthy plant growth and productive harvests.
• Soil Structure: The right blend of organic matter and aeration helps create a loose, crumbly texture that plants thrive in.

Good soil is the foundation—but layout matters too. See how my garden beds, containers, and fruit trees fit together in a cohesive design.

If you’re wondering what the best soil for raised bed vegetable gardening is, the answer is simple—Mel’s Mix.

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

I didn’t come up with this mix; we can thank Mel Bartholomew, the author of Square Foot Gardening, for developing a simple, effective soil blend for raised bed gardening. After reading his book in 2008, I followed his advice for making Mel’s Mix, which he calls “the most important, productive, essential, necessary, critical” ingredient for square-foot gardening success—and it worked!

Mel’s Mix is a tried-and-true solution for raised beds, providing an ideal balance of moisture retention, aeration, and nutrient availability.

What is in Mel’s Mix?

Regular garden soil is too dense for raised bed gardening. Mel’s Mix solves that problem by combining compost, coco coir, and vermiculite to keep the soil light and airy. This blend provides excellent drainage and a healthy environment for plant roots. Here’s the breakdown:

• One part compost: You can make your compost, or if you live in Arizona, the compost from Arizona Worm Farm is a great option. If you use bagged compost, it’s best to mix several different types.
• One part coco coir: A sustainable alternative to peat moss that retains moisture and improves soil structure.
• One part vermiculite or perlite: These materials help with soil aeration and moisture retention.
• 3-5% worm castings: About 1/3 gallon per cubic foot adds beneficial microbes and nutrients. Make your own with in-bed vermicomposting bins or purchase them locally if possible.
• 1/2 cup basalt dust per cubic foot adds trace minerals that benefit plant health.

Depending on your needs, you can also adjust the mix by using up to 50% compost and 25% each of vermiculite and coco coir.

Arizona Worm Farm Raised Bed Mix

In the Fall of 2020, Arizona Worm Farm began offering a ready-made soil mix called “Growing in the Garden Raised Bed Mix.” This mix contains the perfect blend of compost, coco coir, vermiculite, worm castings, and basalt dust. It’s available by the bag or yard. This premixed soil is an easy, convenient option for anyone looking for the best soil for raised beds in the Phoenix area.

Advantages of Using Mel’s Mix for Raised Bed Vegetable Gardening

Mel’s Mix offers several distinct advantages that make it the best choice for raised bed vegetable gardening:

• Simplified Drainage: The combination of vermiculite and coco coir ensures excellent water retention while preventing waterlogging. The soil absorbs moisture, and excess moisture easily drains away when saturated. You can’t overwater with this mix!
• Easy Seed Germination: Seeds germinate quickly in this light, airy mixture, making it ideal for direct sowing in raised beds.
• Minimal Weeds: One of Mel’s Mix’s biggest benefits is its weed-free nature. Since the soil stays light and loose, weeds have difficulty establishing themselves.
• Oxygen for Roots: Healthy roots need both oxygen and water. Mel’s Mix’s light texture allows plant roots to access both, leading to vigorous growth.

How to Combine the Ingredients for Mel’s Mix

There are a couple of ways to mix the ingredients for the best soil for raised bed gardening:

1. Batch Mixing on a Tarp: Spread a tarp on the ground and combine the compost, coco coir, and vermiculite in batches. Once everything is mixed, dump the contents into your raised bed and water thoroughly.
2. Layering in the Raised Bed: You can layer the ingredients directly in the raised bed, mixing well after each addition. This “lasagna style” approach is convenient and works just as well.

It’s a good idea to mix up a little extra of Mel’s Mix to fill containers or top off your raised beds throughout the season. Store it in a large, lidded garbage can for easy access.

Maintaining Your Raised Bed Soil

Over time, the soil level in your raised beds will decrease as the organic matter breaks down. Adding more compost each time you plant is important to keep the soil level topped up and maintain its nutrient content.

• Compost: As the compost decomposes, it enriches the soil with essential nutrients. Keep adding compost to your raised beds with each planting cycle to maintain healthy, nutrient-rich soil. For more information on how to make your compost, check out my composting guide.
• No Need to Replace Coco Coir and Vermiculite: Unlike compost, coco coir and vermiculite don’t break down as quickly, so you won’t need to replenish these components each season. Just focus on adding fresh compost.
• Add in-bed vermicomposting bins to your beds. Worms break down food scraps and create nutrient-rich worm castings right in your garden bed. Read this in-bed vermicomposting guide to learn how to add these bins to your beds.

Using the right mix and maintaining your soil over time ensures that your raised beds remain productive for years. Whether you mix your own or opt for a premade option like Arizona Worm Farm’s Raised Bed Mix, getting the best soil for raised bed vegetable gardening will give you healthier plants, fewer weeds, and bigger harvests.

For more soil resources on my blog, read these articles:

• How to Prepare Your Soil For Planting
• How to Refresh Old Potting Soil
• Soil Testing: When and How to Test Your Soil

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