How to Choose the Right Growing Media for Planter Box Gardens

How to Find the Right Growing Media

Depending on where you live, you'll be looking at bags of growing media with different names or references. Many garden centers and chain stores will have their own mixes, and in some cases, their own brands. The most important thing is paying attention to the ingredients it contains, not what it's called. Be sure to read the label carefully, and look at the percentages, or the order in which the ingredients are listed. We can't overemphasize how important it is to read the ingredients on the label before purchasing any growing medium!

Some typical ingredients in commercial growing media that are safe and preferred for gardening containers include:  

• Sphagnum Peat, which offers excellent water movement and absorption, aeration, and nutrient retention. The label should have this component listed first, or have the highest percentage.
• Vermiculite, an amendment derived from the mineral mica, has a light, fluffy structure that causes it to retain large quantities of air, water, and nutrients.
• Perlite, another amendment, is a naturally occurring volcanic glass that provides excellent aeration and water movement.
• Coir, a sustainable fiber made from ground-up coconut husks, offers excellent water retention properties. It is not recommended to use straight coir, but a blend that includes it as a secondary component is okay.
• Forest By-Products, especially tree bark fines, are okay in small percentages (it's difficult to find commercial mixes that don't contain FBPs). These materials increase moisture retention, but typically decrease available air spaces, while increasing the acidity of the mix.

(From left: Sphagnum Peat, Vermiculite, Perlite, Coir, Bark Fines)

A wide variety of other ingredients may be added to potting media in small percentages in order to provide nutrients. These include blood meal, bone meal, bat guano, dolomitic and/or calcitic limestone, chelated iron, kelp meal, processed poultry manure, rock phosphate, green sand, and worm castings.

In general, any growing medium that's labeled for container gardens, hanging baskets, or seed starting is well suited for EarthBox^® gardening. You'll find that bags of the appropriate growing media are much lighter than bags of topsoil. It’s particularly important to avoid any growing medium that contains soil/topsoil, rock, clay, sand, or any products described as "partially composted.” Topsoil is not sterile, which means it may contain weed seeds, pathogens from manure, or sweepings of actual dirt from mills and stables. Topsoil, sand, and clay are all very dense, which prevents proper aeration and drainage that allow roots to move and grow. Imagine pouring wet concrete in your flower beds—the same can be likened to using the wrong type of growing medium in container gardens.

After years of testing, we determined that growing media that boasts "moisture control" or "water grabbing crystals" is okay to use. Additionally, growing media that already contains fertilizer is acceptable, but you will still need to add granular fertilizer, per the EarthBox® instructions.

Helpful Hint:

Unlike traditional pots or containers, you’ll want to overfill the EarthBox^® container with growing media so that when the mulch cover is pulled tight, there can't be any pooling of water on the surface. Once covered, your EarthBox^® system should resemble a loaf of bread.

Why the Right Mix Matters

1. WICKING, or natural capillary action, is necessary so your plants get the water they need from the reservoir. Sphagnum peat is porous and acts as a sponge to properly absorb the water and help disperse nutrients.
2. DISEASE PREVENTION is important when growing fruit and vegetables that you’ll later consume. While many plant diseases can be spread through the air or transmitted by chewing insects, some start in the soil. By using a sterile growing medium, you eliminate the risk of infecting plants with any soil-borne pathogens.
3. INSECTS AND WEEDS can find their way in to the system through non-sterile potting media, such as partially composted mixes or manure. By choosing a high-quality, commercial growing medium, you are ensuring your plants have a clean environment for roots to grow without the threat of unwanted pests.
4. AERATION is important for healthy roots so they have room to move and don’t rot. Most growing media blends that are suitable for container gardening include several amendments that allow for aeration and drainage, such as perlite.

Helpful Hint:

For the very best results, we recommend you use EarthBox^® Potting Mix, made specifically for the EarthBox^® gardening system. Our proprietary blend is OMRI-certified (Organic Material Review Institute) for organic production, and has been formulated to include beneficial microbes for strong, healthy roots. If you choose to purchase your own growing medium locally, refer to our Approved Growing Media list, and be sure to check the guidelines for what to look for when selecting your own growing medium.

Potting Mix vs. Potting Soil

We've found that growing media can have different names, depending on the geographic region of the country. We call it potting mix, which is the term most often used in the Northeast. In the West it's often known as potting soil, even though it doesn't contain any soil at all. Potting mix in the western half of the country is a product that you mix into the topsoil when planting trees or landscape plants, which makes it unsuitable for EarthBox^® gardening. State and federal regulations don't govern growing media, so label details will vary by product and by region.

The Bottom Line

Ultimately, the mix you use should resemble a professional type of medium. You'll need 2.0 cubic feet of growing media to fill an EarthBox® Original gardening system, or an EarthBox® Root & Veg™ gardening system; and just under 1.0 cubic foot to fill an EarthBox® Junior™ gardening system.

To get the best performance from your EarthBox^® garden, follow the set-up instructions, Planting Guides, and fertilizer guidelines; and you'll be in a good position to maximize your EarthBox^® garden right from the start.

Tell us in the comments: What growing media have you found locally that works great for EarthBox gardening? Don't forget to tell us which region you're from!