Sunlight and water are essential building blocks of life. For plants, soil provides another vital element. It doesn’t just deliver nutrients to hungry fruits, vegetables, and flowers; good garden soil increases the airflow around plant roots to avoid compaction and improve drainage as it retains moisture for basic hydration. Soil also supports a vast ecosystem of microorganisms that boost plant health.
Gardening with raised beds provides more control over the soil, so you aren’t stuck having to grow in and amend subpar soil on your property. However, the best soil for raised beds depends on the plants you want to grow. Many soil types are suitable for a variety of uses, while others are more specific in their purpose.
- BEST OVERALL: Miracle-Gro Potting Mix
- RUNNER UP: FoxFarm FX14047 Happy Frog Potting Soil
- BEST ORGANIC: Organic Plant Magic Compressed Organic Potting-Soil
- BEST TOPSOIL: Michigan Peat 5540 Garden Magic Top Soil
- BEST COMPOST: Charlie’s Compost 10lb
- BEST PEAT MOSS: Hoffman 15503 Canadian Sphagnum Peat Moss
- BEST VERMICULITE: Professional Grade Vermiculite by Plantation Products
- BEST FOR VEGETABLES: New Coast of Maine – Organic Raised Bed Mix
- BEST FOR FLOWERS: MOTHER EARTH Coco Plus Perlite Mix
- ALSO CONSIDER: Mountain Valley Minute Soil – Compressed Coco Coir
What to Consider When Choosing the Best Soil for Raised Beds
Growing flowers and food in a raised garden bed differs from growing them directly in the ground. Consider these key points before dumping dirt into your raised beds.
Raised Bed Height
Knowing the size of your raised bed garden will help you determine how much soil you will need to fill it. Thankfully, there are plenty of useful calculators that can help with this task, taking into account shape and dimensions. In general, the taller the raised bed, the more raised bed soil you’ll need.
Taller raised beds or tabletop designs can eliminate back strain and make gardening more comfortable. Alternatively, you can fill the bottom of a tall ground-level bed with filler like dead leaves or cardboard to minimize the amount of raised bed soil mix you’ll need.
Plant Type and Root Depth
The plants grown in the garden will determine the best raised bed soil depth needed for optimum growth. Generally, a good rule of thumb is to build a raised bed that’s at least 6 inches deep. This depth allows for drainage and retains moisture at levels needed for many common crops. However, some plants have deeper roots than others. For example, if you plan to grow root vegetables like carrots, a depth of 12 inches is preferable.
Raised beds are great for any kind of plant but work particularly well for growing vegetables. Elevating the growing space keeps weeds at bay and the soil warm and prevents compaction. Gardeners also get to start with pristine, neutral-pH soil. However, if you’re using previously used soil, do a soil test to determine whether you need any amendments or fertilizer to renew the nutrients.
Many gardeners have tried-and-true soil mix recipes, but in general, it’s best to avoid settling for uber-cheap bags of raised bed soil. The least expensive bags of soil are often low quality, full of weed seed, debris, and other contaminants, and unlikely to contain many valuable nutrients. A good soil mix contains topsoil, a small amount of substrate, and a significant amount of compost, which contains nutrients that improve soil conditions.
- Topsoil is basically filler soil needed for everything from raised bed gardening to indoor potted plants. It’s not very rich in nutrients but is a necessary component that contains organic matter. If you plan on using topsoil, pour this component into the garden bed first, since it makes a great base layer and filler. Then, cover the topsoil with a more nutrient-rich mix of compost, peat moss, and substrates that will nourish the plants.
- Substrate makes up a small percentage of the soil mix but is extremely important. It helps control moisture content, which is key in a raised bed. Some of the substrates that might appear in soil mixes include peat moss, rock phosphate, vermiculite, perlite, and coco coir. The type of plants you choose to grow will help determine the appropriate substrate to support them.
- Compost is a key component of plant fertilizer consisting of decaying organic matter such as animal manure and bone meal. It can even come from your own backyard pile that consists of leaves, grass clippings, and other yard waste. Using compost from multiple sources is best since a combination provides more diverse nutrients.
Be careful of adding too much peat moss, which can increase the acidity of the soil and throw off the pH balance. Some gardeners prefer to fill raised garden beds with a topsoil-free mix, using equal parts compost, perlite, and coco coir. It makes for a fluffy, moisture-retaining growing medium.
Organic vs. Inorganic
In the world of soil, the term “organic” refers to organic materials such as compost and mulch. “Nonorganic” materials aren’t necessarily harmful. They’re just inert and include things like pebbles, rock phosphate, and perlite. Nonorganic soil that contains no organic matter lacks nutrients but is also free of contaminants. When the terms are used in this way, the term “nonorganic” doesn’t mean synthetic fillers or chemicals; it means that the substances are not nor have they ever been alive.
However, the term “organic” can also mean free of synthetic chemicals and pesticides. The USDA’s National Organic Program (NOP) covers farm practices, including soils and other substances applied to crops like organic fertilizer. In addition, the Organic Materials Review Institute (OMRI), a volunteer organization, lists products that organic farmers can use to produce food. Both the NOP or OMRI list possible soils, amendments, and fertilizers that can be used and still maintain an “organic” garden.
The best raised bed soils contain nutrients that fuel growth. Organic, natural fertilizers include compost, sea kelp, and worm castings. These fertilizers enhance the quality and condition of the soil without you having to worry about contamination. The slow-release properties of organic fertilizers prevent potentially harmful buildup and ensure that your plants aren’t harmed by a flood of nutrients all at once.
Some soil mixes may contain synthetic fertilizers. They provide a quick nutrient boost but don’t improve soil condition and texture like organic options. This is why it is best to choose or make a soil mix with organic nutrient sources.
Our Top Picks
Here are some soil recommendations to help fill garden beds. There are specialized soils as well as general mixes to help plants thrive, including soils from brands long trusted in the gardening world. All you’ll need to do is slip on your gardening gloves, open up the bags, fill up your beds, and get growing.
Miracle-Gro has earned a strong reputation in the gardening world with a wide range of gardening soils, fertilizers, and amendments. The Miracle-Gro potting mix offers a blend of nutrients from a wide range of sources, including processed forest products, peat, coir, compost, meat moss, perlite, fertilizer, and wetting agents.
The compost content has a variety of sources that may include animal manures, composted leaves, grass clippings, or composted bark. A wide range of ingredients provides an equally varied nutrient base that can nourish an assortment of plants. The diversity and inclusion of perlite prevent compaction while improving drainage and aeration. Once applied over quality topsoil, this Miracle-Gro mix has the nutrients to support plants for up to 6 months.
The FoxFarm potting soil contains a mix of microbes with mycorrhizal fungi and sediment. The fungi content enhances the nutrient uptake of the root system by creating a symbiotic relationship with the root mass. Essentially, it expands the root’s reach, promoting their development.
That fungi content gets balanced with sediment that maintains the light texture and aeration needed to let the roots expand as they consume nutrients. The mix contains a pH balance for optimal growth that’s supportive of fruit, vegetables, or flowers. On the downside, this mix holds moisture so well that in certain humid conditions, it may begin to grow mold.
Organic Plant Magic’s organic potting soil contains natural ingredients to feed and nourish plants. This compressed soil can be rehydrated and used as the nutrient layer or applied directly to existing soil without rehydrating. The dry mix alone holds 50 percent more water than regular soil, which is one reason it works so well for raised beds.
The soil contains natural coconut noir, worm castings, mycorrhizae, beneficial bacteria, amino acids, and humic acids. Those ingredients work together for a slow release of nutrients so that plants don’t get overwhelmed. This package requires 12 cups of water to create 2 pounds of compressed soil. The mixture then expands to create 3 gallons of usable soil.
Topsoil fills a raised bed rather than nourishing the plants in it. The Michigan Peat top soil does that with a mix of reed sedge peat and sand. For gardeners who are using dirt from the natural landscape, this mix can loosen heavy clay soils and improve the water retention of light, airy soils.
Sometimes topsoils can arrive with twigs and debris that aren’t harmful but don’t help your garden. The Michigan Peat topsoil (usually) arrives without clumps or these surprise additions, sticking with pure ingredients. However, a word of caution—bags have been known to arrive with stowaways such as frogs.
Charlie’s Compost has natural ingredients composted and ready for plants to soak up nutrients. It contains a mix of chicken manure, cornstalks, forest products, hay, straw, clay, and microbe inoculants. Before being bagged, the ingredients are composted for 8 to 12 weeks, at which time they’re ready for application to the garden.
The blend works well when mixed with other soils or as an additive around plants. If used in direct contact with plants, be sure to use it sparingly: It’s powerful enough to burn delicate plants. There have also been (rare) instances of bags arriving with ingredients that aren’t completely broken down.
This sphagnum peat moss contains 99.8 percent natural ingredients, consisting almost entirely of natural peat. This mix helps break up compacted soils, aerate roots, and improve drainage. However, the peat also holds water for better moisture retention in a raised bed setting.
This bag provides a big bang for the buck. It’s meant to mix with other soils, so even in a large raised bed, it can go a long way. Keep in mind that heavily compacted soils will require more peat to loosen the soil than light, airy soils.
This Plantation Products blend contains a mix of vermiculite grades from fine to coarse. However, it tends to contain more fine-grade particles, which makes a difference in the plants for which it works best—mostly, plants that prefer a high moisture content. With the right soils, it can be used to improve aeration and keep plants well hydrated.
This vermiculite provides adequate moisture levels for seedlings, too. However, the fine grade doesn’t take much moisture to keep plants healthy. Gardeners need to know their plants and soil mixes well when using this vermiculite. In some cases, it can retain too much moisture for plants that are easily overwatered.
New Coast of Maine’s organic raised bed mix nourishes plants with natural ingredients designed for plants meant for human consumption. That doesn’t mean it can’t work well for flowers and inedibles, but when it comes to vegetables, organic ingredients assure top nutrients. It’s OMRI listed, providing an extra layer of assurance that ingredients meet requirements to qualify as natural and organic.
This raised bed mix contains cow manure compost, bichar, worm castings, dehydrated poultry manure, kelp meal, lobster meal, greensand, lime, and mycorrhizae. A varied mix of ingredients balances pH and provides nutrients for an equally diverse range of plants. Keep in mind that this soil is designed specifically for outdoor raised beds. It’s not one to use with indoor potted plants because it won’t provide the right moisture retention or nutrients.
MOTHER EARTH blends coco pith, fiber, and peat in 70 percent of the mix with perlite as the final 30 percent. The perlite creates openings and spaces for better aeration. Its neutral pH provides a nutrient-dense medium in which to start growth.
The fiber content creates a granular mix rather than a long fibrous mix. Seedlings and cuttings do well in this particular kind of soil. However, it doesn’t clump or turn, maintaining an almost fluffy consistency that holds water well, making it a usable mix for mature flowers, too.
Mountain Valley squeezes nutrients down to a compact brick full of goodness. Made of raw coconut coir, this fibrous block expands to a light texture designed to aerate and retain water. At the same time, it provides a nutritious boost for topsoil.
Gardeners can rehydrate the entire block to create 15 gallons of soil or hydrate only the amount needed for a specific project. The compressed packaging stores easily and provides options for a wide range of gardening needs and uses. These compressed blocks come in several sizes to suit most gardener’s available storage space.
FAQs About Soil for Raised Beds
If you still have concerns about filling your raised beds with the best soil, here are the answers to a few common questions about soil for raised beds.
Q. How many soil bags do I need for a raised bed?
It depends entirely on the size and shape of the raised bed. If you know your garden bed’s dimensions, you can plug them into a soil calculator to find out how much you need.
Q. How do you prepare soil for a raised bed?
If you’re buying potting soil in bags, it’s typically premixed, so there’s not much to do other than water it before planting. Topsoils that act as fillers require you to layer substrate and/or compost on top. Once you’ve done that, it’s all about water. Watering the soil prior to planting, using either a watering can or a garden hose, ensures your plants have enough moisture to start growing.
Q. Is topsoil good for a raised bed?
A topsoil product is a great filler, but it’s not designed to be the main nutritive soil in a raised bed. The plants need nutrients, and topsoil is not rich in organic matter like compost or potting soils.
Q. Can I use only compost for a raised bed?
Yes. In fact, the Square Foot Gardening Foundation recommends a compost-only option for gardeners on a budget or those who don’t have access to other mix-ins. However, while this can be cheaper (if you have access to free compost), the soil in a compost-only bed can become compacted.
Raised beds create a fresh weed-free environment for plants to grow and thrive. That clean start depends on the soil used. Narrow down the choices by deciding what plants you want to grow.
From there, design a mix of topsoil, compost, or potting soils that will provide for the nutrient, water, and aeration demands of your chosen plants. Make sure they get sun and the right amount of water to watch the fruits of your labor sprout and grow.