| There is a nurseryman who sells at our local farmers market . Below I have copied his writing explaining his view on potting soils in a newsletter he sends out. I am having better results with the peat/pumice mix when I add some sand and some of my soil than with the usual store bought mixes. As Gary says, the bagged mixes at the stores usually have a more limited life. Using longer lasting mixes allows you to save some work by repotting less often. If I were not growing roses in the ground, I would be using raised beds. We have an elderly neighbor who does all of her gardening in tall brick sided raised beds and it allows her to continue gardening. She can sit on the bricks and work with the plants. A concrete path allows her to use her walker to easily reach the beds. I find that the polyanthas and smaller roses do very well in pots and that young hybrid teas like 1/2 barrels or 15 gallon cans. I don't mind hand watering them but the summer can dry a pot with a large rose in it out in half a day. Dry roses quit flowering in my experience. The other caution is about sunlight baking the sides of the pot and killing roots. Some growers will place a mark on the sun side of the pot so that they don't turn it and cook another area of roots. I prefer just to shade my pots or place them in larger pots so that I can keep all the roots cool and in good health. I'm not trying to sell Gary's soils, but I wanted to share his views on potting soils and the recent use of growers to use a soil with a very short life in order to raise plants for market fast but which cause trouble for the plants/ buyers later whe the plants are installed. We both think bareroot is best for planting in pots and in the ground. From Gary's Newsletter- LHN Potting Soil ACID MIX
1 cubic foot $10
Although this soil was specially created for Azaleas, Blueberries, Camellias, and Ferns it is not too acidic for most plants. I use it in containers for growing all annuals (flowers and vegetables) and plants that require lots of moisture (Hydrangeas and Roses). It is especially valuable for outdoor use in smaller containers (6" or less in diameter) where moisture retention is critical. It can lose about 10-15% of its volume within 18 months as the peat moss breaks down, but retains excellent permeability due to the pumice. It is actually a good soil substitute or replacement when used in the ground. I have beautiful Azalea in Ferns in the ground growing in 100% ACID MIX for well over a decade.
Ingredients: Peat moss & Pumice (about 1:1) LHN Tropical POTTING SOIL
1 cubic foot $10
This soil was created for those plants that require well-drained (highly permeable) soil especially in permanent (at least several years) applications. It is also ideal for all indoor potting applications. We haven't observed any significant shrinkage of its volume over many years of use. It's water retention is about 25% lower than the ACID MIX, so use with caution in small containers outdoors. It is acidic enough to grow most acid-loving plants.
Ingredients: Pumice, peat moss, sand (about 6:3:1) Our potting soils do not have time release nutrients added. The brands that include it can be toxic if moistened and not used immediately. I like to add a time release, like Osmocote, at the time of planting and follow it with organic fertilizers at monthly intervals (we sell these also). Plants potted in our soils can sit in a deep saucer of water for extended periods to provide moisture when you are on vacation. The majority of other brands will rot and stink when left submerged. Also water draining from pots filled with our soil is clear. Many other brands leach out a brownish red color that discolors pavement. When I grow our trees and shrubs in containers, I mix our ACID MIX with construction sand at a ratio of 1:1. Many of our customers like this mixture for the added weight. I like using sand because it is the main component of the finest natural soils and allows plants grown in it to perform better when installed into the landscape. WARNING: OTHER POTTING SOILS ARE ONLY SUITABLE FOR TEMPORARY APPLICATIONS!
A University of California researcher confirms that just about all commercial brands of potting soil are meant for 5 months of use. This short period is due to the temporary nature of the materials chosen. Most potting soils contain composted bark and/or sawdust which lose permeability and gradually become less habitable as the chunks of organic matter decompose and shrink. Apparently the 5 month period is acceptable as most potted plants in the US (other than mild Orange County) freeze or are allowed to die during winter and replaced every spring along with fresh soil. These same researcher also found that most commercial soils, even when fresh, are suitable for growing only a small percentage of extra hardy (tolerant of poor soil) plants. They were able to grow vigorous Impatiens but found that ferns and Cyclamen did poorly. I have also found that most potting soils are not permeable enough to allow vigorous root development, especially when used in large containers. Most potting soils are actually compost. The more you use, the less oxygen is available for root health. This is why some "experts" tell you to increase container size in small increments. Too much fresh compost at one time will suffocate and kill the roots! (see below) In contrast, our potting soils behave more like real soil. The more you use, the better the results. You can use them over and over. Just follow the rules of crop rotation and don't plant the same (or closely related) plant twice in a row. Even more important, you can irrigate freely. Our soils are nearly immune from too much watering. Many of our customers have used our potting soils in the ground, either as an amendment, and often as a replacement with excellent results. Don't give up trying to grow a particular kind of plant until you've tried growing it in our potting soils.
The Science Behind Potting Soil Plant roots require water retention, air exchange, support, insulation, and nutrient storage.
Unfortunately, the first two of these are usually in opposition. Any soil that has high water retention has less air exchange, just because water is taking the place of air. Our Laguna Hills Nursery soils combine peat moss, the best natural material for water storage (Clay holds more water, but won't release it) and pumice, the most permeable natural material (70% space, 30% rock). In our atmosphere the oxygen content is roughly 21% and the carbon dioxide is 0.03%. Research from the University of North Carolina shows that the air in the soil of container plants can be anywhere from 0%-21% oxygen and 0.03%-21% carbon dioxide. High levels of carbon dioxide can inhibit root growth. More importantly the oxygen must remain above 12% for active root growth and above 3% to stay alive.
The problem with most potting soils is that they depend upon the structure of organic matter to create free air flow. Peat moss, bark and sawdust all have great air exchange initially, but because they are not permanent materials, problems eventually occur. Generally (different materials and even parts of organic materials decompose at different rates) within 6-18 months the airflow through the organic materials decreases considerably. Moist organic matter gradually turns to "muck". On top of that the decomposition continues and compounds more toxic than carbon dioxide are produced when the supply of oxygen is compromised.
I've noticed that plants under such poor conditions produce small, off-colored foliage usually showing tip burn (resembling salt burn).
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