There are lots of recommendations about soil for raised beds, but knowing the difference between adequate and superior soil is key to having growing success.
Here’s a breakdown of what we recommend:
1. 50% Topsoil
2. 30% – 40% Organic compost mixed with crushed dry leaves
3. Azomite trace minerals
You might be thinking, that’s it?
We’re going to dig deeper (pun intended) into why this combination works, but first we’ll share a little of our own struggles with this question.
What Not to Do
We started our journey back in the 1980’s experimenting with growing a few of our favorite lettuces. The trouble was we had no idea what we were doing. We planted the seeds in the back yard in a dirt space about 4×4 ft.
How hard could it be, right? I mean, it’s lettuce.
Well, it was a total flop! But a few years later we tried again and got peas and green beans to grow by adding some compost to the soil. Hmmm, the light bulb came on. Compost made a difference.
To say the least, this sparked our curiosity and encouraged us to do some research and learn from successful farmers and gardeners so we could build our knowledge base and apply what we learned from their expertise.
Year by year we gained much more understanding about the soil and its role in the health of what grows in it, how soil structure works, and how it becomes sustainable.
What Type of Soil for Raised Beds?
Now let’s get into why these soil materials work so well.
Quality topsoil made from recycled garden prunings, food products, and/or vegetable trimmings and sand. You definitely don’t want topsoil that is too sandy or that’s so compact it’s sticky or sludgy. Feel the soil for yourself. Not all topsoil is equal, so find a reputable nursery or landscape company to source a good one. This will be 50% of your raised bed soil so be sure not to skimp.
Add organic compost over the topsoil and mix in thoroughly. You will only be doing this thorough mixing the first time you fill your beds. This should be at least 30% or a little more but remember to leave a bit of room at the top of your bed. Use a good, certified compost to ensure its high quality. Find a supplier in your state here.
That makes up most of your bed. As a note, you only need to add topsoil the first time you’re filling the raised bed. Add some compost to your established beds once a year in the early spring before planting. To make your soil take off even more, read our post about compost tea.
You then top it off with a few things to enhance the nutrients even more.
Adding the leaves make a great deal of difference. Your neighbors may be happy to give you their fall leaves if you ask them.
Leaves add a lot of beneficial matter to the soil and feed it. It has carbon which plants thrive on, so this is something you shouldadd every year.
A leaf shredder is the easiest way to cut them into smaller pieces. Just mix in the shredded leaves with your compost before you put it in the bed. It makes the soil airy and light, allowing oxygen to penetrate it.
This is a natural mineral substance found in the Utah desert—specifically, an ancient volcanic ash deposit. AZOMITE stands for “A to Z of minerals including trace elements”. The trace elements of these minerals complement the more commonly replaced nitrogen, phosphorous, and potassium in the garden and help nourish the soil.
You don’t need a lot. Calculate what you need using our handy quick reference chart, which you can download here.
You only need to apply this once a year for maximum benefits. Find Azomite on Amazon here.
By using a combination of these and mixing them with the topsoil and compost, you can start creating an excellent foundation for your crops.
As organic growers, we like to teach people that soil is something to respect and so important, because if you care for it and feed it all the good things it needs, it will provide you with outstanding results.
What Makes Healthy Soil?
The texture of soil can tell you a lot about what’s going on with the structure of it. You want to have loamy, crumbly soil. A loamy soil results from a good structure, or in other words, how all the soil particles are bound together.
Soil that is in optimal health is made up of water, minerals, gases, and organic materials and doesn’t compact too much.
Good soil also contains microscopic organisms, fungi, bacteria, earthworms, etc. This a most important relationship because the resulting produce will be so much fresher and taste a thousand times better than anything store-bought. That’s garden to table!
Raised beds allow you to create the best soil from the start, rich in organic matter, because you can control each input from the beginning. Learn more about the soil food web.
You can continue to improve on your soil in raised beds and make it more self-sustaining year after year as the active food web in your soil continues to grow and thrive.
A Note on Mulch
Mulching the top of your soil is a great way to help retain moisture and keep the soil warmer when it’s cold. The best mulch in our opinion is aged, shredded dry leaves. We talked about this in the soil recipe above but using them as mulch on top of your plants nourishes and feeds the soil.
They break down over time and make the soil even better and healthier, meaning your crops will thrive even more with each growing season.
I wish I’d known this when I was raking up leaves from the yard all those years ago!
Some growers prefer to use straw. At first we used it too, but we stopped after we noticed its tendency to mold, which introduced unwanted bacteria into our beds. So we don’t recommend that.
Pine bedding (such as for horse stalls) can work, and while it doesn’t usually mold like straw it isn’t going to provide the same nutrients as leaves. That being said, use whichever one you like or what’s available to you.
Whether you’re new to gardening or have some experience, you’ll benefit from adding organic matter to your soil and building on the microbial web. Starting somewhere is the key.
Bronte and Candy are a mother and daughter team who have been operating their organic farm, Girly Girl Greens, since 2017. They deliver microgreens on a weekly basis to the local community and chefs in Seattle and Bellevue. For them, growing success is all about healthy soil.
When they’re not writing posts or working with the crops, they like to enjoy the outdoors, spend time with family and friends, or relax with a cup of coffee and a good Hallmark movie.
Read more about them.