After a few years now growing in Self-Watering Containers such as the EarthBox and the EarthTainer, I have concluded that there is no "off-the-shelf" potting medium that is ideally suited to the unique needs of a bottom-up, moisture wicking container. Case in point, both the Moisture Meter is pegged in the "Wet" range, and more relevant the plants themselves are more leggy than they should be:
A "symptom" that I observe is early leaf roll which I attribute to a too wet container mix:
Another "telltale" is premature yellowing of lower leaves and branches:
There is also credible evidence that tomatoes grown in SWCs can have a "watered-down" taste. So, how to address the goal of replicating the ideal in-ground growing experience but in an automated self-watering container.
My guideline in selecting a range of materials to experiment with is based on people being able to easily obtain them at big box stores or places that supply lawn and irrigation supplies. Also, ingredients such as Orchid Mix were ruled out due to their excessive cost. As upward wicking is a "must-have" property, mixes such as "Al's 5:1:1" are good for top down watered containers, however I deemed that a SWC mix required a finer particle composition. But the dilemma is that with too fine a particle size, one will end up with "container goo".
So my quest to find an optimal composition of 3 to 4 ingredients that will provide the best balance of moisture wicking coupled with proper aeration for the root system. The products I selected for the trials included:
Sta-Green Potting Mix (Lowes)
Miracle-Gro Potting Mix
Cactus Mix (containing Pumice)
Decorative Bark Fines
I had to make some assumptions on a range of combinations and ratios as there are something like 7 to the 6'th Power of combinations when doing the math. So here are the 27 combinations I have planted for the Fall tomato trials.
Miracle-Gro; Cactus Mix
Sta-Green; Cactus Mix
Miracle-Gro; Cactus Mix; Perlite
Miracle-Gro; Bark Fines; Perlite
Sta-Green; Cactus Mix; Perlite
Miracle-Gro; Turface; Perlite
Sta-Green; Turface; Perlite
Sta-Green; Bark Fines; Perlite
Sta-Green; Redwood Compost; Perlite
Sta-Green; Cactus Mix; Turface; Perlite
Sta-Green; Bark Fines; Turface; Perlite
Sta-Green; Redwood Compost; Turface; Perlite
My hope is that a number of these combinations will actually "starve" the plants of moisture and will die. I hope an equal number will also show the leaf roll and premature yellowing leaves, indicating too wet conditions. And ideally, I will end up with a distribution curve of healthy, "just watered enough" plants that will replicate an in-ground experience.
If anyone has suggestions for other combinations and ratios, please post them, as I have 4 more empty 'Tainers for trials.
I'll be posting photo updates and identify the specific container mix with each picture as the Fall tomato crop develops.