When my husband and I built our first raised-bed garden a little over 18 years ago, we filled it with some cheap soil from the hardware store. We didn’t really understand how important having good soil to grow our veggies in was.
Well, I can tell you we learned pretty quickly that soil plays a huge factor in the success of a garden. We spent quite a few years trying different methods of gardening until we got it right by investing in the garden soil.
So take it from us: Don’t skimp on soil quality. You’ll end up spending more money trying to fix bad soil. Even worse, you’ll waste entire growing seasons trying to tend plants that are stunted and not producing properly.
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GOOD SOIL MAKES A BIG DIFFERENCE
While good soil can help maintain the overall health of your garden, bad soil can cause a lot of problems. You’ll probably be able to tell within a couple of months whether the soil in your raised beds is good quality or not. If soil conditions are poor, the issues you might experience include the following:
- Your plants are slow to grow and produce.
- The leaves of your plants are changing color.
- Your plants are being attacked by pests regularly.
- It’s difficult to dig in the raised bed because the soil is compacted.
- The soil doesn’t hold together well when you lift it.
- The surface of the soil looks dry and cracked even when it’s recently been watered.
If you notice any of the signs above, there’s probably something off with your soil. It’s a good idea to add some soil amendments. We’ll look at how to amend your soil in a bit.
Healthy soil is dark, almost black. In addition to color, you can also judge soil quality by its structure. It should have some moisture retention and crumble gently in your hand when moist. You don’t want soil that falls apart like sand when you try to hold it, but you also don’t want a clay ball.
EDIBLE PLANTS NEED A SPECIAL KIND OF SOIL
Edible plants are pretty picky about their growing medium—and rightfully so! We’re asking these plants to grow quickly and be full of nutrients for us to enjoy.
If your veggies could fill out a dating profile for their ideal soil match, here’s what they’d say:
- light and fluffy
- full of nutrients
- free of weed seeds (no baggage, please)
- free of bad chemicals
Let’s look at each of these desirable qualities.
The ideal soil should be light and fluffy
Edible plants have pretty delicate little root systems. Think about this: Most of them are annual plants that finish their life cycles within their first year in the garden, often within just a 90-day period. These plants don’t have time to develop strong root systems that can push through compacted soil the same way a live oak or even a crepe myrtle do. They need something light and fluffy that they can sprout and grow in.
Light and fluffy means lots of air pockets. If a plant’s roots encounter obstacles or can’t push through a compacted soil, its growth will be stunted. That being said, plants do need enough dense material present to give some structure to the soil and hold their roots in place.
The ideal soil should be full of nutrients
If you want your fruits and veggies to be full of nutrients, you’ve got to give them some nutrients. One way that plants get nutrients is, of course, through the soil. That is, unless they’re growing in soil that’s too dense, dry, sandy, or just void of all vitamins and minerals. Give your plants a nice, rich soil if you want healthy produce.
The ideal soil should be well-draining
If you’ve done a bit of gardening already, then you know how important good drainage is to plant health. Soil that holds too much water can cause plants to rot. The ideal soil for a raised bed retains moisture without letting roots sit in a bathtub of water for too long (because they really don’t like that). One great bonus of soil that retains a bit of moisture is that it keeps the surface of the garden cool longer, which is great during the heat of summer.
The ideal soil should be free of weed seeds
One reason you don’t want to go scoop a bunch of your native soil (the soil in your backyard) and dump it in your raised beds is because it could contain weed seeds. Edible plants are super sensitive to competition, and weeds will just rob them of important resources they need to thrive.
The ideal soil should be free of bad chemicals
Perhaps the most important reason to pay attention to the soil you put in your raised beds is stuff you want to avoid: herbicides, pesticides, and synthetic fertilizers. Whatever’s in the soil can leach into your plants. So don’t fill a raised bed that will be home to your future food with any soil that’s been treated with chemicals you wouldn’t eat.
All right, with that in mind, let’s look at the actual materials that combine to create a raised bed soil your plants won’t want to break up with.
THE BEST RAISED GARDEN BED SOIL RECIPES
You shouldn’t fill your raised beds with potting soil or garden soil intended for in-ground gardens (which would be too dense). While you could buy a ready-to-go soil mixture from your local nursery, I recommend mixing your own soil or checking out the mixes at a landscape supply store. That way, you know you’ll end up with a soil that will nourish your herbs, fruiting plants, root vegetables, and leafy greens and that won’t contain anything synthetic or harmful.
I recommend combining your main ingredients for each mix on a tarp before dumping it into your raised bed.
We’ve got two mix options for you.
Soil Recipe #1
Our ideal raised bed soil mix is 40% topsoil, 40% compost, and 20% coarse sand, plus a little something extra added to the top. All the ingredients for this loamy soil can be found at local landscape suppliers, nurseries, and garden centers—don’t worry. I guarantee this tried-and-true recipe will keep your edible plants happy and healthy for years to come! (You can even use this same mix in your container gardens.)
Let’s look at each of these soil elements in more detail so you understand their importance.
Topsoil is usually a loamy mix of clay, silt, and a little bit of sand. You have topsoil in your backyard—it’s the top layer of your native soil. I typically don’t recommend using this topsoil in your raised beds, however.
The clay found in topsoil is dense enough to give some structure that will support and hold the roots of your vegetable plants as the leaves grow large and heavy. The silt provides lots of nutrients.
Sand is super permeable and has lots of large particles in it. Most topsoil mixes have some sand but not enough. Adding sand to your soil blend, therefore, helps with water retention. You need the soil to hold water for long enough that plants can absorb it, but not so long that your garden becomes a swamp. Sand doesn’t really have a lot of essential nutrients though, and that’s where our third ingredient comes in…
Compost is made from organic material that has broken down over time. Giving your plants organic compost is the best way to mimic nature because plants growing in the wild get most of their nutrients from decomposed, leaves, sticks, insects, and even animals. All the vitamins and minerals that were once in those living things can help nourish your garden in compost form.
Besides adding tons of nutrients to the soil, compost is also super permeable and full of air pockets. Some plants like lettuces can grow in straight compost, but larger plants will need that top soil mixed in to give their roots more structure than loose compost can provide.
A Little Something Extra
The last soil ingredient for your raised bed garden is just some worm castings added to the top. This is a great organic way to give your plants a boost of nutrients. If you have some on hand, you could also use composted rabbit or chicken manure instead of worm castings.
Your local bulk landscape supply store will most likely have a loamy soil mix very close to the one above. I recommend paying them a visit so you can talk to them in person, tell them what you want, and look over their options. The employees should be able to tell you the composition and ratios of the different bulk soils they sell. Being able to feel different options is really important before you make a large purchase. You can even bring home samples to try.
Soil Recipe #2
This recipe is from Mel Bartholomew’s book Square Foot Gardening. He engineered this soil blend to be ideal for raised beds, both holding moisture but draining really well. It’s also super easy to mix. The negative, I would say, is the cost of the last two ingredients.
Mel’s Mix contains:
Vermiculite helps to keep the soil light and fluffy. Peat moss or coco coir helps to retain water. You can add “a little something extra” (see above) to this mix, as well.
Make sure to measure each component by cubic feet, rather than by weight. You’ll need 9 cubic feet of each ingredient per cubic yard.
HOW TO CALCULATE SOIL FOR RAISED BED
1. Measure the width, length, and height of your raised bed in feet.
2. Multiply W x L x H to get the total cubic feet of soil needed to fill your raised beds.
Ex: An 8ft x 4ft x 2 ft raised bed would be 64 cubic feet.
3. Add the total cubic feet of each raised bed that needs to be filled.
Ex: Two 8ft x 4ft x 2 ft raised beds would be 128 cubic feet.
4. Divide the total cubic feet of raised beds by 27 to get the total cubic yards needed.
Ex. 128 cubic feet is equal to 4.74 cubic yards.
If your soil needs exceed 1 cubic yard, I recommend buying in bulk instead of purchasing bags.
THE BEST WAY TO AMEND RAISED BED SOIL
For those of you who’ve already filled your raised beds, it’s not too late to get great, fertile soil for your plants.
If you’re noticing signs of bad soil in your garden, an easy way to improve the soil quality without dumping it all out and starting over is to instead just remove the top 6″ or so of soil from the bed. Pick one of our soil recipes above and mix enough to fill this top portion of your garden. (Calculate how much soil you need by multiplying W x L x 0.5). That way, the majority of your plants’ roots will grow in the great soil up top.
When dealing with struggling vegetables, there are several beneficial soil amendments you can consider adding to improve the soil quality.
Here are some of the best soil amendments you can use:
- Compost: Choose between mushroom, leafmold, vermicompost, and composted manures (rabbit, chicken, turkey, cow, or horse)*. You can also make your own from kitchen scraps and yard waste.
- Peat moss or coco coir: These are lightweight organic materials that enhance water retention and aeration in the soil. They can improve soil structure, especially in sandy soils, and increase nutrient availability.
- Rock dust: Rock dust, such as granite or basalt dust, contains minerals and trace elements that can replenish nutrient levels in the soil. It enhances soil fertility and can benefit plant growth.
*Word of Caution:
If you plan to use cow or horse manure, make sure you know the grass/hay they were fed is herbicide and pesticide free. Otherwise, you risk contaminating your garden. I’ve seen several gardeners end up with plants that just wouldn’t grow. For this reason, I prefer to use rabbit and chicken manures.
Soil Amendment Cheatsheet
Here’s what you can add to amend soil issues. (There’s no need to grab all the items. Pick whichever is readily available to you.)
If your soil is too sandy and not holding on to moisture…
Add compost, peat moss, or coconut coir.
If your soil is too compacted…
Add compost, coarse sand (not play sand), peat moss, or coconut coir.
If your soil is lacking nutrients…
Add compost or rock dust.
You can do a soil test through your local county ag extension or several online vendors to see more details about your soil and what is lacking.
Soil testing is my last resort. I stick with adding compost and making sure I am feeding my plants when needed and this has always worked for me.
HOW TO MAINTAIN HEALTHY SOIL THROUGHOUT THE GROWING SEASON
Even if you start with the absolute best garden soil, you’ll still need to replenish the soil nutrients from time to time. Your edible plants are hungry, and they’ve been sucking all the good stuff out of your soil. It’s up to you to add it back in.
The best way to do this is simply by adding 2- to 3-inches of compost at the beginning of each gardening season before you plant something new. Leafmold or mushroom compost are great options for replenishing nutrients, but really, any fresh, finished compost from a nursery will do.
If you notice your plants are falling over or look like they need more support, you can work some more topsoil or clay into your soil to improve its structure. If you notice the leaves of your plants are turning yellow or plants are rotting, then it’s probably more of a permeability issue. Work some sand into your soil.
RAISED BED SOIL FAQs
Can I fill a raised bed with potting mix?
Potting mixes are often created specifically for certain plants like cactuses or fruit trees. Some mixes might not have any actual soil in them at all. A potting soil for a houseplant, for instance, could be filled with bark or be nothing but peat moss. While it’s not going to hurt your garden to toss some potting mix into your soil, you need way more organic matter inside your raised beds than just a potting mix can give.
Can I reuse soil in a raised bed?
You only have to fill your raised bed with great soil one time; after that, all you have to do is refresh the top every season. The soil level in your raised beds will sink a bit over time due to the soil being compacted by heavy rains and regular watering.
The best time to raise the soil back up to the top of the bed is when you’re planting something new. Just add a 2- to 3-inch layer of fresh compost. This is also a great way to replenish the nutrients in the soil.
Can I fill my raised bed with topsoil from my backyard?
I typically don’t recommend using your own topsoil for a couple reasons. First of all, the materials in topsoil differ by region. Unless you know the makeup of your native soil, you might add too much sand to topsoil that’s already sand-heavy or end up with way too much clay in your garden.
Secondly, most of us can’t guarantee that our yards haven’t been sprayed with pesticides, etc. You wouldn’t want to use topsoil that’s been treated with chemicals that will get into your edible garden.
Lastly, you’re more likely going to introduce weeds into your raised beds, and we want to keep weeds at bay to make your gardening chores a lot easier.
LETTUCE HELP YOU GROW
I’m so happy that I figured out the importance of having good soil in my vegetable garden before I gave up on gardening entirely. Take it from me: Don’t skimp on soil for your raised beds. It’s worth the extra money to ensure the ultimate success of your garden.
Start your garden the right way by booking a one-on-one coaching or design consultation session with us. We’ll help you fill your raised beds with the best stuff possible. Our goal is to leave you with a productive and beautiful kitchen garden space that will flourish and bring you joy for years to come.