I've built a raised garden bed and would like to know what types of soil or mix I should use to fill it with? Should it be a mixture of top soil and compost? I'm looking for an affordable option.
I'm in Birmingham, Alabama and the bed is 3' x 6' x 16". I have 3 of these beds. Mostly growing veggies (spinach, beans, carrots, etc) and herbs.
The reason most people build raised garden beds is because their existing top soil isn't good enough to grow in. So definitely don't use your existing soil.
People that follow Square Foot Gardening tend to use Mel's mix which is 1/3 Vermiculite, 1/3 Peat Moss and 1/3 Compost from varied sources. This seems to be the best mix if you're doing square foot gardening.
Some people use just straight compost. Others heavily amend their existing soil with compost and other additives. Some garden centers and other suppliers sell bulk "garden soil" which can mean different things to different people. There's also bagged "garden soil" from local and national suppliers. A lot of them seem to be mixes of topsoil and compost with other additives. The bags usually mostly compost and peat based.
There are also things like Pro-Mix Organic Vegetable and Herb Mix and other similar products from other brands. This is the type of stuff commercial greenhouses seem to use. A lot of them are peat moss based it seems.
People will have different opinions but basically you don't want to add "soil". Other growing mediums will give you more benefits in terms of tilth, water handling and nutrition.
I've been considering this same question and it looks like I'm going to go with Mel's Mix as I'm planning on doing SFG. Even if I wasn't I'd probably use something similar which would be mostly compost, peat and either vermiculite or perlite.
What are you currently using in your other raised beds and how are the plants doing in them?
Also consider coconut coir instead of peat moss. People have issues with the sustainability of peat moss
If I would start new soil, I would take a few things into account:
These things work together and makes the soil balanced. Nature does it out of the box, so trying to mimic nature is a good start.
Moist (water) is used to transport nutrients deeper into the soil. It also transports micro-organisms further around.
Oxygen keeps everything alive. The soil needs oxygen too. It's for the micro-organisms to multiply and to 'burn'. No processing is going on without the oxygen. Cell division thrives on oxygen. Micro-organisms have cells too, they want to spread!
So, with that being said... What to choose? In the answer above Mel's Mix is mentioned. Very good choice! There are other comparible mixes or alternative ingredients available. Look around for a mix of dirt, clay and compost. The dirt can be somewhat coarse for the oxygen. Clay is good for the moist. The compost is for starting up with the micro-organisms.
I suggest to watch "Back to Eden" about topping off the soil with wood chips. Organic, clean, mixed wood chips. This is very natural coverage of the soil. It will keep it moist when needed and give of water in times of hot weather. It will also soak up excessive water. Further it will be coarse enough to let even more excessive water seep through to the deeper soil.
You can add wood chips later too. Or add additional every (other) year, so it will build up natural layered structure. This is awesome for healthy soil. After a while you don't have to do anything anymore than just let nature do the work. Not tilling, no chemicals, no plowing, no fertilizers. The "do-nothing" method like Masanobu Fukuoka calls it.
I also suggest to read the book "Teaming with microbes". This will give you an idea about what lives in the soil, how to support it and how it enhances your plants and trees.
For advanced soil, I would look into the mycelium/mycorrhiza and things like bokashi. This way your plants will grow strong and healthy!
