What is the most over-looked ingredient in a good potting soil?
How do I go about making or finding a professional potting soil for professional results?
Can I use a professional potting soil approach in a box / bed garden?
In this Blog I’m going to include some information I’ve learned from an article on the web site, www.allergyfree-gardening.com, titled ‘The Real Dirt on Potting Soil’. written by Tom Ogren who is the author of five published books, has a M.S. in agriculture / horticulture and taught horticulture for twenty years. In addition to this he started growing when he was five years old, 57 when he wrote the article and somewhere between then and more recent times he owned two wholesale – retail nurseries. He mentioned a couple of potting soils he favored but could no longer find them and began to buy less costly potting soils and amending them considerably. I will only draw on the points he made in that part of the article, but I recommend this as a good read in general, especially for amending and or making a professional potting soil.
We have put into practice, and have been getting good results by applying Tom’s principle approach to amending or making professional potting soil. In a paragraph subtitled Perlite, he points out the pros and cons of high drainage using Perlite. These pros and cons are, better root development via more aeration, but will require more frequent watering. Aeration is key, and air is the over-looked ingredient.
Here is how it works: The main functions of the growing media are to provide nutrients, water, gas exchange and anchorage. Lets first focus on gas exchange because this involves air. The gas is a phosphorus that is the bi-product or production of microbes breaking down organic matter. The microbes also provide root growth hormones. Think of your potting soil as yogurt culture. The bacteria is friendly and it needs air to thrive. Bad bacteria will be killed or kept in check by air. So air is key. In the past, the practice has been to increase drainage with Perlite. This is because Perlite provides air and increase drainage. Air via Perlite also keeps the roots from drowning and keeps the soil from compacting. Both water and compacted soil displace air. However, high drainage results in increased run off or waste of nutrients and water. Also, maintaining moisture is key for sustaining a bio-intensive root zone. So, the down side to high drainage is that run off of water and nutrients are costly and messy. Air, on the other hand is free (at least for now) and so are the gases that the microbes produce. There are other materials that work better to increase both aeration, moisture and nutrients in a potting soil. Though they are not widely distributed in the major retail stores yet, they are worth the trip to the hydroponic store, and worth the increase cost of shipping if buying on-line. They are less expensive and work better in the long run. These are referred to as sustainable and soil-less mediums.
The two most common are boiled rice hulls and Coir (ground coconut shells). Boiled rice hulls replace Perlite, and Coir replaces Peat Moss. All of the plants in the pictures in this article are growing in potting soil that is approx 2/3 Coir and Boiled Rice Hulls.. Coir has safe Ph levels, is more coarse for aeration and absorbs more water and nutrients. Likewise, Rice Hulls also absorb moisture and will hold their shape (see Sink or Swim blog on rice hulls) to trap air. Because they are organic, they will slowly decompose and provide nutrients. As mentioned, Boiled Rice Hulls also absorb moisture and cost about $1.50 per cu ft when purchased on site in small volumes.
What is a Good Professional Vegetable Potting Soil Mix?
- 4 shovels of dampened coir,
- 4 shovels of dry boiled rice hulls,
- 1/2 shovel hardwood ash , optional for middle pH.
- 1 shovel top soil,
- 8 cups Garden Tone organic vegetable microbial plant food by Espoma,
- 1 cup Triple Superphosphate, or Triple Phosphate, and or 2 cups organic bone meal.
- 1 cup organic blood meal for a jump start.
- 1 cup pelletized lime for pH balance.