The type of soil needed to grow a garden bed is usually a mix of 60% topsoil, 30% compost, and 10% potting soil (containing perlite, peat moss, and/or vermiculite). Some people also add organic fertilizer. The depth of this soil depends on what you plan to plant in it.
A good, healthy soil mix that promotes a natural ecosystem where plants thrive is essential to raised bed gardening. If you want to know about this combination and some other suggestions,
How much soil do I need for my raised garden bed?
First, since you're buying one or more beds, you may need to buy soil in bulk. It's much cheaper and you can always mix it at home and mix it later if you have extra. After all, there is always something to settle down.
You can also usually find pre-prepared compost in bulk, too. If you want good prices on compost and mulch, check with your local landfill and waste management company. Maybe your municipal waste removal department has a leader. In our area, landfills in local towns are sold in cubic feet, usually half the price you pay elsewhere.
When buying soil in bulk, it is measured in cubic feet or cubic yards. That means you need to break high school math again! Remember, when it comes to a standard raised garden bed, you are dealing with a rectangle.
Remember how to get the area of a rectangle? side x the other side = area²
Example: 4 feet x 6 feet = 24 feet²
You do this, then multiply that area by the depth of the space you need to fill. Remember, we use feet as a measurement. So when you measure inches, you need to divide it by 12 (since there are 12 inches in a foot).
Example: We have a higher bed, so I need to put 24 inches of soil on it.
24 inches ÷ 12 = 2 feet now 24 feet² x 2 feet = 48 feet³ or 48 cubic feet.
If you need to change it to cubic yards, remember that 27 cubic feet = 1 cubic yard. So you need to divide the number over cubic feet by 27.
Example: 48 cubic feet ÷ 27 = 1.78 cubic yards
did you know?
Topsoil that is sometimes mixed specifically for plants is called loam. Loam is soil made from a balance of three main soil types: sand, silt, and clay. Because this combination of soil types is known to retain proper moisture, oxygen, and nutrients, it creates the perfect soil texture for plant growth.
What is the best formula for soil for raised garden beds?
60% topsoil/loam
30% compost
10% potting soil (you want a potting soil mix containing perlite, peat moss and/or vermiculite)
Keep in mind that these ratios are approximate, but I've searched a lot of extension service publications and gardening websites to find this out, and the percentages tend to stay around this. I'm going to use it on my own bed and see what happens.
If you want to add fertilizer to this mix, just add ½ cup per 5 square feet of soil.
What do I need to know about your soil?
Some locations may not have access to good quality topsoil. If this is your case, then you may need to use an alternative. Throwing away 50%-50% of the compost and potting soil mix can replace it. Or, if you have some topsoil but a limited amount, you can always mix it with a 50%–50% mix to give it a fresh look.
Speaking of fresh soil - you can definitely refresh the old soil. When I transplant other plants from one place to another, I tend to find old soil. Also, the soil in the raised bed will settle with the seasons, and then you will lose soil volume as you take out the various plants.
When I find old soil, I dump it on the bed I want to replenish. Then, I grab enough new potting soil to fill the bed I like. I use a patio rake on the shorter/larger beds and a hand tool on the higher beds to mix all this soil together.
You can also add peat moss to raised beds. However, it should not exceed 20% of the total portfolio. Why? Because peat moss is naturally acidic. So you probably don't want to grow vegetables in it.
The purpose of a raised bed is to help reduce gardening work by limiting weeding and providing the best, most fertile soil for your bed. So don't step or compact the soil! The fluffy, well-drained soil you can develop is a huge advantage, giving you vigorous plant growth. If you compact it, you reduce aeration, slowing the activity of earthworms and beneficial microbes beneath the soil surface.
You can add a fine sawdust mulch on top of the soil for better moisture retention. As wood chips break down naturally, they add more nutrients and bulk to the soil.
