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?
For making or amending potting soil with medium commonly available, read the article previously mentioned 'The Real Dirt on Potting soil' by Tom Ogren. The 2 cu ft. Vertical Eco Garden potting soil mix, given here, in increments of a classic Norman Rockwell garden shovel, is the mix being used to grow all the plants in these pictures. This mix starts with 4 garden shovels of compost forest material, leaf or plant compost. I used my own forest compost but a good 'off the shelf' substitute is often labeled Garden Soil. Here is the rest of my soil recipe:
- 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.
If you are growing varieties of vegetables, general measurements are fine. You can get more specific when growing one plant type. For this, I would use the recommended soil culture and check the pH. A big advantage of using Boiled Rice Hulls and Forest compost in a potting soil mix is its longevity.
But what about plant anchorage in this loose growing media that doesn't compact or cake up like peat moss? In the Vertical Eco Garden design, roots grow through a layer of Geotextile material to access the water and nutrients in the vertical rooting chamber, and this anchors the plant. This unique feature allows the use of a very aerated and moist media needed for a rich microbial environment. The Geotextile felt like material also provides air and the roots like it. For a bed garden, I suggest a layer of straw or other structure for the roots to grow through.
Concerns with Peat Moss
I am often asked, what happened to the Topsy Turby (spell?) upside down hanging tomato thing? Well, I don't know. But I suspect it was the combination of high drainage (perlite with peat moss) and inexperienced gardeners who forgot to water frequently. You see, Peat moss is hydrophobic. Once it dries out and cakes up, its hard to get water back into it. Coir absorbs water. We will post a quick U tube video demonstrating this by dropping a chunk of each in water so you can see what it does. The Peat moss floats forever like a little raft. The coir absorbs water just like a sponge. Actually, this is the main reason for frequent watering when using peat moss, and I suspect is probably the main cause of problems contributing to over-watering. Finding the balance between damp and wet is precarious. In the VEG system we use drip irrigation set on low to maintain proper moisture, and this works great with Peat Moss based potting soils.
The practical solution for utilizing run off / drainage in the Vertical Eco Garden design was to give all the plant roots shared access to a continual vertical chamber containing the root growth media. Gravity does the rest. It works. And it looks like I need to make a big organic salad.
And then of course, since it works so well we decided to expand on that.
For a bed, box or conventional garden that is a min of 12 inches deep, you can use the Tom Ogren, Vertical Eco Garden and I am sure there are others, approach to potting soil that utilizes air, thus a more bio-intensive soil. The differences are in the amount of soil, labor and cost. Your results on the ground will be determined also by Mother Nature. This differs from the Vertical Eco Garden design. It is more resistant to heat, drought, torrential rain and foraging. In the picture above, there will be a wide variety of 125 high yield plants in a garden space of 15 sq ft using a total of only 28 cu ft of potting soil, or 7 cu ft per each VEG. This soil can be easily removed through the bottom openings and amended for recycling. A 4 ft X 8ft X 12in height box will need 32 cu ft to grow 32 plants.
The enviro friendly non toxic, treated Geotextile fabric can last for a very long time, much longer than un-treated lumber that is placed on the ground. And we need to turn that around. In addition to burning less of the carbon based molecule that is ideal for construction and materials, lets save the trees that are better left alive to absorb carbon. OK? There is no weeding or cultivating required with Vertical Eco Gardening. Evaporation removes heat and heat is not absorbed or stored over night as with ground gardens because the plants provide their own shade. Organic bug control? less pest come from the pavement than the ground. There is less waste as the excess water and nutrients draining from the upper plants feed the plants below. The Vertical Eco Gardens in the above are mounted on wheels and can be relocated for more or less sun, (note the lettuce or shade tolerant plants face due east for only morning sun). The gardens in this picture can be rolled into a building at night for a longer growing season.
The over all cost goes way down each consecutive year they are used. The loose media also facilitates automated soil exchange of the potting soil and should open the door to Commercial Urban Farming as soon as this is viewed as more of a business opportunity rather than an identity. Also, if you like to garden and would like to have more free time on more important things, please visit us at www.verticalecogarden.com to learn more about The Vertical Eco Garden and maybe it will spark some more ideas.
