Hydroponics ensures there is ample oxygen along with that water. There are many hydro techniques, but they all involve a good ratio of water to oxygen. Some use a bucket of water with an aerator, others use a misting system with roots that hang in the air, others use alternating water, no water etc.

In a potting mix the only place for oxygen is in the spaces between particles. Those spaces can be filled with air or water, but not both at the same time. The term drainage refers to how quickly and completely those spaces empty of water and fill with air.

The 5-1-1 mix would never be too wet for tomatos or any veggie/annual/flowery thing for that matter. "Too wet" simply means the mix maintains water in some portion of those spaces between particles. The greater the percentage of spaces that gravity doesn't remove water from immediately, the closer to 'too wet' the mix is.

Avoiding 'too wet' is simply a matter of using ingredients of a sufficiently large enough particle size. Above 1/8" particles can't hold water in those spaces so the mix would be considered fast draining. Particles in the 1/16th inch range would drain well, but might have a small amount of standing or 'perched' water at the bottom of the pot. Smaller than that and the percentage of spaces remaining filled with water after gravity has moved all it can out of the container increases.

I think everyone makes the 5:1:1 mix a little differently. If the bark is well-composted and you work hard at it, I think you can over=water to the point where you could make a case for being able to say it CAN get too wet, but if you're reasonable in your approach to watering, it won't be a problem. Ideally, the soil will hover at right around the separation point between a soil that does and a soil that doesn't support a small amount of perched water.

The answer to your question about "... why soil mix that is too consistently wet in a container can cause problems in growing tomatoes, while growing tomatoes hydroponically, i.e. roots always submerged in water, does not cause problems?" lies in understanding the difference between parenchymous and aerenchymous tissues.

The root cortex and pith of plants grown in soils with ample O2 are composed of mostly parenchyma, which serves primarily as a (food) cache. Some % of the parenchyma cells of plants that have been flooded or have had their roots intentionally immersed in water, which creates hypoxic conditions (low O2), die from lack of O2. Their dissolution creates continuous air spaces between the shoot and the roots. This tissue this forms is called aerenchyma, and it facilitates O2 movement between roots and shoots, allowing normally terrestrial plants that are able to form this type of tissue to survive in aquatic environments. The problem is, the tissues formed are not well-adapted to making the transition back and forth from an aerobic environment to hypoxic or anoxic conditions.

The short answer is that roots that are adapted to function in water fare poorly or don't function at all in well-aerated soils, and roots that form in well-aerated soils die in soils devoid of air and choked with the gasses that saturate these soils; although, they often CAN make the transition to hydroponic culture via the mechanism described above.

Al

Thanks Justaguy and Al.

I have four 1/4 inch wicks suspended from a five gallon container with 5:1:1 mix. The wicks are always in water. Any chance the wicks could make the mix too wet?

Doubtful. I use a mix slightly more water retentive in SWC and it doesn't get too wet.

Agree

Al

Thanks again, one more question: some roots have grown
through the bottom of the container through the holes and synthetic wicks and into the water resevoir. Could the roots in the water resevoir adversely affect plant growth, compared to if the roots were not in the water?

I don't believe so. It's not uncommon for roots in SWC to extend into the reservoir. While it's not the healthiest environment for them I can't imagine it's any worse than pruning those roots off.

The way I figure it, if they can function at all and provide any benefit to the plant, it's just a bonus ;) It's their fault for growing into the reservoir anyway. Gotta show the plants some tough love! ;)

Justaguy....thanks very much!

chal,

What I found last year was that with the roots freely allowed to enter the water reservoir, the tomatoes when cut open, contained more moisture that those I've grown in traditional raised beds. Taste was also negatively affected.

I now use layers of Landscape Fabric to impede the roots from freely growing down in to the water reservoir, and this has reduced the over-water condition to my satisfaction. You might want to experiment with a layer or two of Landscape Fabric to see if it works in your situation.

Raybo

Raybo-
Thanks...I'll try it.
Tom