Container Gardening: The Best Soil for Containers

Why Soil Selection is Important

Think of soil as the foundation for container gardening and your plants. Just as a strong house needs a solid base, plants need good soil.

“Soil is the make-or-break factor in container gardening. You can water and fertilize perfectly, but if your mix is wrong, plants won’t thrive.” — Mark Bolt, VP of EarthBox.

You must establish a strong root system because it helps your plants grow and thrive. The soil feeds the roots, so it must provide three essentials: water, nutrients, and air.

Here's why soil selection matters:

• Nutrients: Soil provides essential nutrients for plants to grow healthy and strong.
• Water Management: The suitable soil helps plants soak up water without drowning or drying out.
• Root Health: Your soil allows roots to breathe and spread quickly, leading to better plant growth.

Can You Use Topsoil in Gardening Containers?

No. Topsoil belongs in the ground, not in pots. It’s dense, heavy, and holds too much water, which can suffocate plant roots. So do your plants a favor—put the shovel down.

The UC Master Gardener Program recommends avoiding garden soil in containers, even high-quality garden soil, because it lacks the aeration that container plants need to thrive. Instead, use potting soil specifically designed for containers.

Issues with Garden Soil in Containers

Here's why you must avoid using it for container gardening:

1. Compaction: Topsoil is coarse and heavy, often including stones and clay. When used in gardening containers, it compacts. That reduces aeration and drainage, both of which are disastrous for plant health.
2. Diseases: Natural soil generally houses weeds and other seeds, not to mention disease-causing pathogens. You'll pass those unwanted items onto your containers and plants.
3. Nutrients: Topsoil likely falls short of nutrients for your plants. It may contain some from decaying matter, but unless you've added more, it falls short of the nutrients needed for potted plants.

“Topsoil is meant for the ground, not pots. It’s too dense, holds too much water, and puts roots at risk.” Mark Bolt, VP of EarthBox.

What is the Best Soil for Container Gardens?

The best soil for container gardening is a potting mix specifically designed for containers. Unlike garden soil, potting mixes are specifically engineered to promote drainage, aeration, and moisture retention, all of which are critical for root health.

Look for mixes that include:

• Sphagnum Peat Moss: It helps hold water moisture and improves aeration.
• Perlite and Vermiculite: They add air space to the soil for better root health. They're also essential for improving drainage in your gardening containers.
• Compost: It provides organic material for your plants, containing essential nutrients.

“The best container soils balance air, water, and nutrition. That’s why our EarthBox systems use mixes designed to hold moisture while letting roots breathe.” Mark Bolt, VP of EarthBox.

What Are Some of the Better Potting Mixes?

To find out, Epic Gardening conducted a field trial comparing 14 leading brands. They grew the same variety of pepper plants in 5-gallon grow bags using only potting mixes labeled for container use (no garden soil or topsoil).

Each mix was evaluated based on:

• Plant height
• Leaf color and appearance
• Branching
• Flowering
• Fruit yield and quality

Top 5 Potting Mixes:

1. Miracle-Gro Potting Mix
2. Vigoro Potting Mix
3. Miracle-Gro Organic Container Mix
4. Miracle-Gro Moisture Control Potting Mix
5. Recipe 420 Potting Mix

These results highlight the significant impact that the right potting mix can have on plant performance and yields, even when identical watering and care are provided.

EarthBox Potting Mix

That’s precisely why EarthBox created its own potting mix, specifically engineered to work with the EarthBox gardening system. Unlike generic bagged mixes, the blend is designed to:

• Provide the right balance of moisture retention and aeration
• Support consistent root growth throughout the season
• Pair with EarthBox fertilizers and dolomite lime for long-term nutrient delivery
• Eliminate the guesswork of choosing from dozens of off-the-shelf brands

“We designed our mix to take the variables out of container gardening. It’s consistent, reliable, and proven to maximize yields in our system.” Mark Bolt, VP of EarthBox

Independent testing, such as this Epic Gardening trial, demonstrates the significant impact of soil choice on yield. EarthBox eliminates the guesswork with a proven mix designed explicitly for its system.

What's the Difference Between Potting Soil and Soilless Potting Mix?

Many people view potting soil and potting mix as interchangeable terms. Not true.

Potting soil may or may not contain soil. However, potting mix is always soilless as a growing medium. The advantage is that the potting mix is sterile and safer for plants. It doesn't contain pathogens, such as fungi, that can harm your plants.

Homemade Potting Mix

If you're more adventurous or particular about potting mixes, you can create your own homemade potting soil for container gardening. You'll use many of the same ingredients in bagged mixes. The upside is that you can customize those ingredients to achieve the best balance for your plants.

The main ingredients include:

1. Peat moss for aeration and water holding capacity.
2. Coarse sand to improve drainage and aeration. Unlike peat moss, sand doesn't hold water.
3. Perlite to add drainage. It also keeps the soil light and fluffy, allowing it to hold air. You can also use vermiculite in your mix. However, it can hold water and nutrients, but it can be compact if the wrong grade is used.

How to Make Homemade Potting Mix

You can make soil-based or soilless potting mixes.

When creating a soil-based mix, it is recommended to purchase sterilized loam soil, which eliminates concerns about disease, insects, and weeds. Again, avoid taking soil directly from your garden beds.

To create the soil mixture, follow these steps:

1. Add a gallon of sterilized loam soil to a bucket.
2. Add a gallon of moistened peat moss to a gallon of coarse sand, perlite, or vermiculite.

Combine the ingredients in the bucket and adjust the mixture to achieve a loose, well-drained consistency. You can change the mix by adding sand or peat moss to alter or refine the soil's texture.

Soilless Homemade Potting Mix

Remove sterilized loam soil from the ingredients and replace it with a soilless, homemade mix. Use two gallons of peat moss with two gallons of perlite or vermiculite. Then, mix them thoroughly.

With either soil mix, you'll also want to add slow-release fertilizer and small amounts of limestone.

Limestone raises the mixture's pH. It comes in two forms: calcitic limestone and dolomitic limestone. The former includes calcium to strengthen the plant's cell walls. The latter adds magnesium and calcium to the soil.

Start by adding two ounces or four tablespoons to your mixture. You can adjust the pH to achieve the desired level.

Compost - An Essential Ingredient of Most Container Soil Mixes

According to the University of Maryland Extension, compost delivers the full spectrum of major and minor nutrients plants need to grow, bloom, and produce.

What is compost?
Compost is a dark, crumbly, earthy-smelling material made from decomposed leaves, grass clippings, wood waste, and manure. It’s teeming with beneficial microorganisms that improve soil health and help feed your plants. That is why compost is usually a great ingredient to add to your container garden soil mix.^*

*We do not recommend using compost in EarthBox gardening systems. Particles can fall through the aeration screen and prevent the wicking system from working properly.

Why Compost Works So Well in Most Containers:

• Nutrient-rich: Compost contains natural sources of nitrogen, phosphorus, potassium, and micronutrients.
• Replaces peat moss: While peat moss holds moisture, compost supplies nutrients and improves water retention, making it an ideal substitute.
• Reduces pollution: Composting recycles nutrients that would otherwise wash into waterways, helping protect the environment.
• Safe and weed-free: Properly made compost reaches high enough temperatures to kill weed seeds and pathogens.
• Versatile: You can use it solo or in blends:
  • • 100% compost
    • 100% soilless mix
    • 50% compost / 50% soilless mix

Does Compost Replace Fertilizer?

Not completely. While compost supplies nutrients, those nutrients are released slowly over time. For best results, especially with heavy feeders like tomatoes or peppers, you’ll still need to supplement with fertilizer during the growing season.

What About Soil pH?

Most vegetables thrive in a pH range of 5.5 to 7.0. Some composts test above 7.0, but studies show there’s no need to adjust pH artificially. Nutrients in compost remain available across a broad range.

Do Different Vegetables Require Different Soils?

That said, certain crops, like tomatoes and peppers, perform best in slightly acidic soil (6.2–6.8). In those cases, you may benefit from fine-tuning your mix by adding amendments such as sulfur.

Herbs, on the other hand, tend to prefer neutral soil (around 7.0).

How Deep Should the Soil Be for Gardening Containers?

Soil depth depends on the plant's roots. Here's a general guideline:

• Small plants need 6-8 inches of soil.
• Medium-sized plants need 10-12 inches.
• Large plants like tomatoes need 18 inches or more.

That also means you'll need to find gardening containers that can handle those depths. EarthBox, for example, offers several selections with varied depths:

• Original Gardening Boxes: The company's tried-and-true planting boxes are 11 inches deep. That's a perfect depth to house the most popular vegetables.
• Herb Planting Boxes: At just over seven inches deep, you can plant basil, thyme, oregano, mint, sage, and other herbs in these gardening boxes.
• Vegetable Planting Boxes: Their 15-plus inches work for root vegetables with more substantial soil requirements. In these gardening containers, you can plant carrots, beets, onions, turnips, potatoes, and radishes.
• Tomato Planters: These planting boxes are 11 inches and perfect for tomato plants. Additionally, you can purchase a tomato-growing kit that provides everything you need to grow ripe, juicy tomatoes.

Can Potting Soil Be Reused?

Yes, but with a caveat.

Potting soil breaks down over time, losing nutrients, aeration, and structure. By the third year of reuse, you’ll likely notice stunted growth compared to fresh soil. That’s because organic matter compacts, air pockets disappear, and fertilizer additives are long gone.

How Long Does Potting Soil Last?

Unopened bags of potting soil typically last about six months before the quality begins to decline. Once in use, soil in containers should ideally be refreshed every year.

“Soil isn’t one-and-done. As it breaks down, you lose structure and nutrition. We recommend mixing in fresh growing media and new fertilizer and dolomite lime each season. As long as you do that and your plants didn't suffer any serious plant disease, you can reuse the potting mix indefinitely in our EarthBox gardening systems.” Mark Bolt, VP of EarthBox.

How to Refresh Potting Mix

To reuse soil successfully:

• Fluff it up: Remove last year’s roots, stems, and debris. This improves porosity (the “fluffiness factor”) that roots need.
• Add fresh potting mix: Top off with at least 25% new soil each season to restore structure and nutrients.
• Replenish fertilizer: Most added fertilizers only last three to six months, so supplement with a slow-release fertilizer and dolomite lime, depending on your crops.
• Check pH: Over time, peat-based soils can become acidic. Adding lime helps balance the pH for most plants, or you can save older soil for acid-loving crops like blueberries and azaleas.
• Consider a revitalizer: Products designed to recharge potting soil can improve water retention and add nutrients.

EarthBox is Your Source for Successful Container Gardening

EarthBox has been a go-to source for container gardening for three decades. Its growing systems let you successfully grow vegetables, fruits, and herbs, even if you don't have a green thumb.

Commercial farmers developed the system and then tested it in labs. So, you'll enjoy maintenance-free container gardening that can double your yields compared to garden beds. 100% guaranteed.

Choosing the right soil is half the battle. Pair it with a proven container system, like EarthBox, and you’ll maximize yields with less guesswork, regardless of your gardening experience.