[BajaMitch]

This past season I did 16 experiments dealing with various mix recipes and other physical aspects. I found an optimal recipe for drip irrigated containers and self watering containers.

For the drip irrigating buckets, my results showed that a mix of 2 parts compost, 2 parts potting mix, 1 part peat and 1 part perlite was optimal. Drains well, has plenty of CEC (Cation Exchange Capacity), and holds good water retention and air retention. It costs me $.52 per "wet gallon" of this mix. My cost of ferts is over and above this mix cost. The compost has a great deal of macronutrients which significantly keeps my cost for ferts down and provides micronutrients as well. without deteriorating the wicking ability of the mix. I use 4.5 gallon buckets, but in order to fill the bucket with "wet mix", I have to use 5.68 gallons of dry mix. The dry mix reduces in volume when wetted by 21%. So, for a 4.5 gallon container, my mix cost is $2.35 for each 4.5 gallon bucket of wet mix.

For the self watering containers in the same 4.5 gallon buckets, my mix recipe is 3-1-1: 3 parts potting mix, 1 part peat, 1 part perlite. I actually put 1 qt 6 fluid oz of dry compost in the mix and take that away from the volume of dry potting mix for some micro nutrients and some macronutrient boost. The total cost of that mix is $2.21 for 3.5 gallons of wet mix or $.63 per wet gallon. I have to make 4.42 gallons of dry mix, then it wets down to 3.5 gallons with 1 gallon of volume left for the water reservoir.

This mix provided good wicking ability, plus good air and water retention and plenty of CEC.

I tried a bunch of different mix ratios and kept track of the growth, plant health, tomato production and determined that the above mix recipes definitely generated the best results at the optimum cost.

On another point, I second what AKMark says about container volume. He uses fertigation with liquid chemical ferts that do not need breaking down by microbes. Since he feeds the plants every day with just the right amount of plant-ready chemical ferts, the plants do not need a lot of grow media. It is akin to hydroponics where the root ball doesn't need to grow much past a 1 to 1.25 foot root ball and certainly doesn't need to grow any giant tap roots. By keeping the rhizosphere of the plant replenished on a daily basis with plant-ready chemical nutrients at just the right ratios, his plants get everything they need exactly when the need it...nothing less and nothing more. The "nothing less and nothing more" is critical, BTW. An imbalance in the nutrient ratio and either over fertilizing or under fertilizing and you lose plant optimization and your results drop dramatically. It is a balancing act. It is also and unstable equilibrium meaning a small departure from the right balance in any direction will get you poor results.

Next year I am going to experiment with a combination of slow release ferts, compost and some plant ready chemical ferts in various ratios to each other while maintaining the exact same chemical ratio that AKMark's fertigation is based on. I will rescue the plants if they show signs of deficiencies or excesses by turning to increased application of plant ready chemical ferts as needed. Next year's experiments will include comparisons of Self-Watering containers to drip irrigated containers using the approach described hereinabove.

This is all very fascinating to me. I have spent nearly 3 hours a day for the past year researching and working on fertilizer compositions, mix recipes, physical aspects such as containers with and without holes, optimizing root generation of cuttings, and meticulously tracking my experiments' components such as pH, grow media temps, hours of sunshine, day time and overnight temps, exact tracking of irrigation quantities per container, etc., etc., etc.

Not sure, but I think next year will be the year I complete the major part of goal which is to determine the lowest cost container method with repeatable reliable results. Right now it looks like I can do it for $2.70 to $3.30 per container which includes all costs for everything.