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Raised Bed Gardening Soil: What Makes the Garden Grow

This author has been a successful gardener for many years. From splitting hosta plants to growing vegetables, he offers several techniques.

Compost bins with palettes

Compost bins with palettes

Gardening is great fun for young and old alike. This activity is both physically and mentally demanding, as well as rewarding, from the garden design to the planting and, ultimately, harvesting of your vegetables. This article is about raised bed gardening soil—read on to learn the formula you can follow to make a great garden.

Raised Beds for Gardening

The raised bed concept in the home garden is not a new concept. This is standard practice for small to mid-size gardens. Using raised beds in a vegetable garden will prove to provide you with several advantages.

  • A great option for anyone with limited space.
  • Various heights allow easier access to vegetables.
  • Raised beds organize and make a garden more attractive.
  • Controlled environment for your vegetables.
  • You have more control over what goes in and what comes out.
  • The soil in a raised bed improves over the years.

Types of Raised Beds

Below are three of the most common methods used for raised beds.

Wooden Boxes

This is the most popular of all raised beds. Lumber sizes come in 8’, 10’, 12’, and 14’ lengths. The widths are 4’, 6’, and 8’. This gives you a variety of sizes for your area. The most common size is the 4’ x 8’. raised wooden bed. Along with the length and width of the lumber will be the depth of the raised bed.

Many vegetables need certain depths for proper growing conditions. These numbers range from 6”, 8”, 10”, and 12”. It is highly recommended to purchase your lumber pressure-treated. You will find that they will last for years. (find a short video to show how to make a raised bed using wood)

Metal Tubs

Galvanized corrugated steel construction. This type of raised bed will last for years. They come in a variety of sizes and depths. Metal beds come in rectangular and circular shapes. Very easy to work with.

Concrete Blocks

Concrete blocks for raised beds can be a lot of work to make them attractive. The advantage of this method is that it is extremely strong and permanent. The first layer needs to be level. For this type of bed to be functional, two additional stacks may be required. Single open blocks measure 8”x8”x8”. Regular open blocks measure 6”x 8” x 16”.

Just offset stacking them will give a secure structure. As a decorative measure, colored patio blocks are a nice finishing touch.

The Dirt on Dirt

Before you go out and purchase a bunch of things, look around your property and take inventory. Almost everything on the ground is worth something to your garden beds. Let's look into the "dirt on dirt."

Lawn Debris

Collecting lawn debris, such as leaves, straw, grass clippings, small branches, etc., can be stored for later use. While planning your garden projects, don't forget that these materials can and should become an amendment to your raised bed soil during the fall and winter. This gives time for the materials to decompose over several months. The great thing about this method is that it’s free, and depending on how much you collect will determine if you need additional amendments.

Compost

Compost is an essential element for your raised bed gardening soil. We can add to the list of materials from our lawn debris. These items come from our kitchen, which we usually call "garbage." Table scraps, vegetable peelings, eggshells, coffee grounds, etc. These materials contribute to building compost.

When collected, these materials start the process of breaking down and can eventually be added to our raised bed soil. Compost helps the soil absorb and retain nutrients and moisture. This is a continuous cycle in building great soil.

Manure

Manure is both fertilizer and soil amendment. This amendment slowly releases nutrients into the soil. Manure contains nitrogen, phosphorus, and potassium. Composted cow manure is a great additive for your raised beds in the fall. I like to use chicken manure during the growing season to sprinkle around the plants as a great boost.

Mulch

Mulch is used to retain moisture, help reduce weeds and keep the soil cool. It also makes the garden bed look attractive and uniform. Good soil supports the plant but also anchors the roots. Good soil will provide the necessary nutrients, water, and air plants need.

Compost Bin Container

I find that having a container that I can use to collect my compost materials is the best method. On a daily basis, almost anything that is leftover from the kitchen table can be put into the composter.

A portable compost bin container is a fantastic receptacle for this method. Below is the model that I have, and it works great. I put my "garbage" in it, add some dirt, and leaves from time to time, rotate the tumbler every day, and let it do its thing.

My wife thought that it would stink to high heaven. Not in the least! No smell!

If you are willing to dedicate more time, build yourself three separate compost bins using palettes. This method is designed for the gardener with a lot of material to collect for building compost.

This is a three-level system that needs daily and weekly turning as the compost decomposes.

Fresh compost

Fresh compost

Best Soil Plan for a Raised Bed

There are many types of soil that one can have in a garden. That is why we want to fill our raised beds with a particular formula to get the best combination for our vegetable plants. Additionally, building good soil ensures a reliable supply of crops year after year.

Most homeowners don't have the proper soil for gardening. This is one of the reasons why raised bed gardening is the best solution for the home vegetable garden. The materials you use for the best soil for your raised beds are:

  • Vermiculite - 20%
  • Compost - 40%
  • Peat moss - 30%
  • Top soil - 10%

A Little Soil Chemistry!

Remember that your number one goal as a gardener is to build the best soil you can. Knowing a little about the chemistry of your soil will stay with you forever.

Soil pH is a measurement of how much acid and alkaline is in your soil. This measurement is rated on a scale from 0 to 14, with zero being the most acidic. The higher end of the scale of 14 indicates the most alkaline. The number seven shows neutrality. You will want to strive for a pH level between 6.0 and 7.0.

  • Nitrogen (N) - helps make proteins for strong leaf and stem growth and a dark green color
  • Phosphorus (P) - promotes root and early plant growth, setting blossoms for developing fruit
  • Potassium (K) - promotes the overall strength of the plant along with disease and stress resistance

Below is the soil tester that I use for all my plants, inside and out. Very easy to use. Insert the probe in the soil, select which test you would like, and have instant results. The soil tester will tell you what additives you are missing in your soil. In addition, it will indicate if your plants are getting enough water and light. Every gardener should have a soil tester.

Filling Your Raised Beds for the First Year

Soil for your garden is like baking a cake. For the best cake, you need to have certain ingredients that go into the mix. When filling a raised bed, you need to think of it as a layer cake. And we do this by filling it with certain layers of material. Below is a list of ingredients for our raised bed mix. Or a layer cake!

First Layer = 40%

The first layer of material is the nonessential matter like cardboard, small branches, sod, and grass clippings. These materials are just for filling. They don’t hold any significant nutrients for your plants. But they will decompose over time and contribute later. Depending on the depth of your raised bed will determine how much of this material is necessary.

Second Layer = 25%

A second layer can be brown dirt, clay, sand, and topsoil. Very little, if any, nutrients for your vegetables. This layer will support the layers above and give your raised bed the height it needs. In time this layer will contribute to the total richness of your raised bed soil.

Again, how much of these materials will be determined by the depth of the bed. The goal is rich black soil. Also, I am basing the measurements of a 24” deep bed. The next layer will be the good stuff.

Third Layer = 30%

Our Raised Bed Gardening Soil: What Makes The Garden Grow depends on this third layer. It is a mix of compost, manure, peat moss, vermiculite, and potting soil.

Mix these materials thoroughly as they all work together for the correct chemical balance. This layer is where your plants get the nutrients they need. 8–12 inches of these materials are at the top of your raised bed. Now you are ready for your vegetable plants.

Fourth Layer = 5%

It is very important to remember this last layer. Mulch consists of decomposed wood products. It helps keep your soil cool, reduces weeds, and makes your garden beds look uniform and attractive. Not putting mulch on after your plants are in will lead to problems down the road.

Filling raised bed - 4' x 8' x 24"—first layer

Filling raised bed - 4' x 8' x 24"—first layer

Filling raised bed - 4' x 8' x 24"—second layer

Filling raised bed - 4' x 8' x 24"—second layer

Filling raised bed - 4' x 8' x 24"—third and fourth layers

Filling raised bed - 4' x 8' x 24"—third and fourth layers

Calculating Soil Volume (Third Layer)

There is a really effective and easy method for calculating the third layer. It doesn’t matter if you have one raised bed or ten when determining how much soil you will need.

Square and rectangular gardens are the easiest to calculate when you need to determine the soil volume you require. It usually involves three main measurements: length, width, and height.

Note: Height refers to the depth of the raised bed, and the volume is usually calculated as follows:

  • V = L x W x H

You can easily calculate the amount of soil mix by using the following three steps.

  1. Measure the length, width, and height.
  2. Multiply the three measurements. This number will give you the cubic feet.
  3. Divide the cubic feet by 27 to get the number of cubic yards you will need.

V refers to the volume of soil that you will need for your raised bed. If we are using the third layer of a raised bed, then this would be the volume measurement for the height.

An example of this measurement is as follows:

Let’s say your raised bed is 6 feet long by 3 feet wide by 1.4 ft high (deep). Using our formula of V = L x W x H can be calculated this way.

  • Length = 6 ft
  • Width = 3 ft
  • Height = 1.4 ft
  • 6 x 3 x 1.4 ft = 25.2 cubic feet
  • 25.2 cubic feet divided by 27 = 0.9 cubic yards of soil mix

Let’s look at another example using this same formula.

A raised bed measuring 4 feet long by 2 feet wide by 2 feet high.

  • Length = 4 ft
  • Width = 2 ft
  • Height = 2 ft
  • 4ft x 2ft x 2ft = 16 cubic feet
  • 16 cubic feet divided by 27 = 0.592 cubic yards of soil mix
best-vegetables-to-grow-in-raised-beds

Avoid Making These Mistakes

Over the years, I have learned many things about gardening. The most crucial ones came from the mistakes that I made. Here are a few for you to avoid.

  • Not enough soil in the bed: Make your raised beds deep enough for the plant roots to grow. In this instance, it is better to have and not need than to need and not have.
  • The wrong soil ingredients: Don't cut corners. Your vegetables need nutrients to grow well. They will tell you if you cheated them on nutrients. They just won't give you any veggies.
  • Improper watering techniques: Set up a good watering schedule for your plants. If you have the time invest in a drip hose watering system on a timer. You won't regret it.
  • Not enough sun: Most plants need 6 to 8 hours of full sun to grow. Planting in the shade will defeat your purpose for gardening.
  • Lack of planning ahead: Planning your garden projects is a must. Have a good Plan A and a better Plan B.
  • Planting the wrong vegetables: Learn about the vegetable you wish to grow. Knowledge is king and knowing which vegetables grow well next to another is very important. This is called companion planting.
how-to-grow-squash-vertically-step-by-step-guide

In Closing

The success of any garden is the result of careful planning. Learning about the popular methods of gardening detailed in this article—from the design of your garden area to the mistakes to avoid—will start you on the right foot.

This content is accurate and true to the best of the author’s knowledge and is not meant to substitute for formal and individualized advice from a qualified professional.

© 2022 Reginald Thomas