I moved some plants to this method over the summer. I love it and I think the plants do too. So far peace lily, dieffenbachia, "lucky bamboo" and some other random experiments. I used the DE "napa floor dry" of Al's gritty mix fame, as my media.

Essentially, all container growing is semi-hydro, or at least it's closer to hydroponics than it is growing in the ground, and why coarse soils that don't hold significant volumes of perched water are more productive than soils that do.

If you DO decide to go semi-hydro, you should fertigate (fertilize + irrigate) regularly from the top. Filling the reservoir regularly and not flushing the soil allows fertilizer salts and the dissolved solids in tap water to accumulate in the medium. This is a problem with 2 faces. It not only unnecessarily raises the o/a level of dissolved solids, it can also quickly cause the ratio of nutrients to each other to become badly skewed, which causes the plant difficulty in absorbing particular nutrients. For instance, an imbalance in Ca & Mg (too much of either in relation to the other) can make it difficult for the plant to absorb one of the nutrients. Too much P can make it difficult to absorb several nutrients, but especially Fe (iron). The scientific term for nutritional imbalances that affect the uptake of other nutrients is 'antagonistic deficiency'.

You can see that as we move away from soils with a preponderance of fine particulates, as in peat-based soils, the problems associated with poor soils also start to disappear. Watering problems, high salt content, lack of adequate aeration, compaction, the ability to maintain a healthy state of fertility..... all go away. It just makes it far easier to consistently maintain plants in a healthy, attractive condition.

And don't use organic forms of fertilizer if you're going to go semi-hydro. Odors, algae growth, and gnat activity are all markedly more likely and noticeable if you use organic nutrients for hydrocultural apps.

Al

Thanks to both of you for contributing your input to this. I think semi hydro is an under utilized approach. In addition to the benefits of keeping a constant moisture level, I like that it is CLEANER than potting plants in soil.

Al, I can see how your gritty mix follows the same kind of principles as semi hydro. I like that this allows me to control the nutrients but also flush the pots out easily.

My next big experiment is to see if some of the most challenging houseplants will do better in semi hydro. When I grew a gardenia in soil, I noticed that the main downfall of the plant was its fussiness about soil moisture.I have also read that gardenia is prone to root disease. Since I know that gardenia can root in plain water, I am going to dare to try a gardenia semi hydro and see if I can actually keep one alive!

I am also going to try some calatheas semi hydro. I am wondering if the semi hydro technique might help with their desire for high humidity.

Many plants can grow roots that contain a different kind of tissue. Where roots in a solid medium get their oxygen from pores in the medium itself, roots growing in water must transition to a specialized tissue (aerenchyma, rather than parenchyma) that allows the plant to bring oxygen to the roots from the top of the plant. If you want a more scientific explanation I'll provide it, but what's important to understand is the root tissue of plants in soil is different than the roots of plants growing in water. The problem with the differentiation is the roots are very poor at making back and forth transitions. That's why soggy soils are so hard on plants. They ask the plant to grow under water for a few days, then in an aerated environment until the next time the plant is watered. It doesn't work - roots rot and die, or root function is limited by lack of oxygen.

In soils that go back and forth from soggy to reasonably well-aerated, roots die during the soggy period. Then, when aeration returns to the soil, the plant spends energy it would otherwise use for growth, flowers, fruit .... to regenerate the lost roots. This cycle of root death and regeneration is very hard on the plants energy reserves, and robs the plant of vitality.

**************************************************************

There's no question low humidity taxes a plants ability to move enough water to keep up with hydration demands, but the key element in most cases is how efficiently the roots work. If root function is inhibited by a lack of oxygen in the root zone, it can't move water. Keeping humidity high helps to mitigate the symptoms caused by the primary offender - poor root function. Keeping roots healthy does much more for a healthy appearance than maintaining high humidity, but that's not to discount the value of keeping as much moisture in the air as is practical.

Al