Container Gardening: The Best Soil for Containers

A person mixes potting soil ingredients preparing to plant container garden

Container gardening is a fantastic way to bring the joy of growing fresh produce to even the smallest spaces. But your success starts from the ground up. Literally.

Your soil selection has everything to do with healthy plants and how much they yield. So, let's get dirty with some pointers on the best soil for gardening 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.

You must establish plant roots because they help feed your plants. Well, the soil feeds those roots. And your soil ingredients must deliver some essentials, namely 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?

You might think you can grab a shovel load or two of topsoil from your garden bed to use in containers. Don't. Ever.

Topsoil belongs in the garden. Although it works perfectly fine in that garden environment, it's a poor choice for container gardening. This also applied to bagged topsoil.

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 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 nutrients needed for potted plants.

What is the Best Soil for Container Gardens?

Look for a potting mix designed for containers. A local garden or home center carries numerous brands and types of potting soil. It contains ingredients designed to enhance aeration, drainage, and moisture retention.

Typically, it includes some or all of these critical items:

  • 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.

Companies like EarthBox specializing in container gardening offer suitable soil mixtures. They even have planting kits with pre-measured essentials that retain moisture while providing superior plant nutrition. You can even adjust the fertilizer to fit your growing needs.

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

Many people view potting soil and potting mix as the same thing. 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 like fungi that can harm your plants.

Homemade Potting Mix

If you're more adventurous or fussy about potting mixes, you can create 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 to hold air. You can also use vermiculite in your mix. However, it can hold water and nutrients but compact if you use the wrong grade.

How to Make Homemade Potting Mix

You can make soil-based or soilless potting mixes.

When creating a soil-based mix, you'll want to purchase sterilized loam soil, eliminating disease, insect, and weed concerns. Again, avoid taking soil directly from your garden beds.

To create the 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 mix for a loose, well-drained mixture. You can adjust the mix by adding sand or peat moss to add or subtract from the soil's texture.

Soilless Homemade Potting Mix

You remove sterilized loam soil from the ingredients with a soilless homemade mix. Instead, 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 to achieve the desired pH.

Do Different Vegetables Require Different Soils?

Whatever your mix, you'll want to adjust the soil based on what you intend to grow in your container garden. Plants are a lot like Goldilocks! They look for just the right mixture to grow the best.

For example, tomatoes, peppers, and other vegetables prefer slightly acidic soil. You'll want to target between a 6.2 and 6.8 pH. As a point of reference, neutral soil has a pH of 7.0. You can add sulfur to the soil mix for greater acidity.

Tomatoes also prefer well-drained soil that's nutrient-rich. They're heavy feeders, so you must keep them well-fertilized.

On the other hand, herbs prefer a soil pH of 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 handling 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, and radishes.
  • Tomato Planters: These planting boxes are 11 inches and perfect for tomato plants. Additionally, you can purchase a tomato growing kit that gives you everything you need to grow ripe, juicy tomatoes.

How Long Does Soil Last in Container Gardens?

It depends on the container gardening system you use. If you make a DIY container garden, the shelf-life of potting mixes might be less than you think. For example, unopened bags of potting soil can last six months before their quality diminishes.

Typically, you'd want to replace the soil in DIY gardening containers every year or two. Why? First, peat moss can compact, reducing aeration and water retention. Second, the container's nutrients diminish from plant consumption and drainage.

You can replenish the soil in a DIY container garden by adding 50% fresh potting soil. You can add more organic matter and slow-release fertilizer to bolster the soil's nutrients.

If you instead use a pre-built container gardening system like the EarthBox, the existing potting mix can be re-used for many years, as long as there are no confirmed cases of blight or other plant diseases. The reason for this is that by following their planting instructions and process, the growing media gets better for your plants. This is due to the recommended addition of dolomite every growing season, which allows for better concentration and readily available elements to be taken by the plant.

EarthBox is Your Source for Successful Container Gardening

Tomatoes growing in an EarthBox container gardening system with attached trellis

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 yields versus garden beds. 100% guaranteed.