Growing Media & Amendments

Guide to Growing Media

When picking out the right growing media for the job there are several things to consider.  I imagine you found that out the first time you walked into your local grow shop or garden center, and thought you were just there to pick up some “good dirt”.  After reading the labels, you actually became more confused than before.  I mean what the heck is Yucca extract or Mycorrhizae good for? I am pretty sure my grandma didn’t have any of those ingredients in her garden’s dirt cocktail. Well chances are she did, or at least something that did the same job, she just didn’t recognize them as such.

So here is the scoop on growing media. First off, it needs to be stated that technically all of the “potting soils” sold in grow shops and gardens centers are actually soilless mixes because they do not contain any of the natural soil components including: sand, silt or clay. But we will discuss them in more detail in just a bit. After you have chosen your media, watering and fertilizing habits are key to prosperous grows.

Soilless Growing Media

Soilless growing is great for use in both indoor and outdoor settings, and has easily become the method of choice for growers because of its superior properties, and ease of amending. Soilless media allows for the ultimate control over desired inputs, drainage properties, pH and nutrient control. The most common soilless potting mixes are made with one of two bases.

The most common base is Coco Coir. This media is 100% natural and made from coconut husk fibers. It is generally a finely ground blend with some desired variation. It has the perfect air to water ratio, and thus is hard to overwater. Coco coir also has a high CEC encouraging optimal nutrient release. Due to its superior qualities, Coco coir allows for rapid growth similar to hydroponics. Keep in mind that with Coco coir bases, Cal-Mag supplementation will be needed. We recommend either Canna or Botanicare’s coco coir based potting mixes.

If it is not a coco coir base, it is generally a peat based mix. Peat is partially decayed and dried sphagnum moss. It is extremely high in organic matter, and retains moisture better than coco coir. Thus, it is not as forgiving if you overwater. By itself, peat usually has a very low pH, between 3 and 5. In potting mixes you can help balance the acidity with the addition of lime. For a peat based potting mix our go to of choice is Pro-Mix.


Once you’ve decided which base is best for your application, next you have the soilless amendments. Amendments help define the final properties of the mix, which is customized for maximum harvest results. Common amendments include the following, and added for the following reasons.

  • Perlite: increases drainage and aeration
  • Dolomite lime: buffers pH, provides calcium and magnesium
  • Worm castings: natural source of nitrogen, enhances beneficial microbe population
  • Mycorrhizae: symbiotic growth on and around roots, increases water and nutrient uptake
  • Azomite: buffers pH, slow release of micronutrients
  • Oyster shell: buffers pH, provides calcium
  • Yucca extract: natural wetting agent, increases uniform water absorption of planting mix
  • Dried kelp: source of potassium and natural plant hormones
  • Alfalfa meal: organic source of balanced fertilizer, amino acids and triacontanol
  • Feather meal: source of organic slow release nitrogen
  • Fishbone meal: organic source of phosphorus and calcium

True Soil

Now onto “true soil”. True soil is used almost exclusively in outdoor growing. Its composition varies from place to place and consists of countless natural and native components. These components include mineral particles- sand, silt, and clay (45% collectively), air (20-30%), water (20-30), organic matter (1-6%), microorganisms and the ever pervasive weed seed.  Organic (carbonaceous) matter, often referred to as humus, is composed of decaying plant and animal remains. Microorganisms include both beneficial and harmful bacteria and fungi. And weed seeds are one of the grower’s greatest foes. Not only are they a nuisance, but they also compete with your crop for water and nutrients.

Since the composition changes from area to area, the properties change along with it. True soil with a healthy ratio of soil particles and organic matter will have good drainage. If the soil is compacted with low aeration, roots and plant growth will struggle. Conversely, if there is too much drainage, growth will also be hindered due to a lack of water and nutrient retention.

Along with your soil composition changing from area to area with true soil, so will your soil fertility. The most important aspects of soil fertility to keep in mind include the presence and amount of organic matter, macro and micro nutrients, pH and CEC. There are various amendments and fertilizers that can help you achieve desired results in an outdoor setting. For more information on any of these click the links above.