chong

It appears to me that everyone is arguing over apples and oranges. As a few have already posted, they have found various definition of hydroponics. And each one says it is a method of GROWING plants in mineral nutrient solutions, without soil. Growing is the "apple". Air-layering is a method of plant PROPAGATION. So, Propagation is the "orange".

The origin of air-layering was the observation that some types fallen trees after a storm, whose branches have touched or been embedded in the ground, continue to grow their own roots, and were able to be separated from the main, to live out on their own. Initially, this phenomenon was duplicated by partially breaking part of a branch, and wrapping the injured part in moist common soil wrapped in impervious material, e.g., old tin can, heavy canvas, etc., and enough openings for aeration and periodic watering. Nowadays, common soil is still used in Marcotting. I have a friend in the Philippines who is a full time farmer, and he has a video on how to propagate black pepper by air layering, that shows him putting "dirt" in a ziplock bag and wrapping the soil around node on the black pepper vine, before closing it off with the ziplock bag and rubber band. I believe in the US, practitioners of this method are mixed/divided between soil and soilless potting media.

Soilless potting media, I distinguish from just media. I use a soilless potting media for plants that I intend to send out of state - Fisons Sunshine Mix No. 1. It consists of coarse peat, perlite, vermiculite, and pumice. Using this for hydroponics would be counterproductive. The peat holds so much moisture that it would take several days for it to dry out. Watering it every 15 minutes alternatively would keep the medium wet constantly.

Hydroponics, as the name implies (hydros=water, ponos=labor), is a method using water with nutrients. When defined as "without soil", it does not preclude sand nor pebbles/pea gravel, which according to the USDA is, in fact, soil. So this growing method is mostly about the growing of plants in water containing the nutrients. The medium is only for support of the plant itself.

On propagating plants from cuttings in water, I'm sure there are many of you that have done this before. Especially, if you've ever ordered Plumeria cuttings. Besides Plumeria (Frangipani), I've done this with Cestrum Nucturnum, Carrissa Grandiflora, Wild Strawberries, some citrus, black pepper, Datura, Brugmansia, even orchid. And yes, with roses, also. With roses though, the plant will develop as the original, however, it would not be very cold hardy because the roots will freeze. So you will have to bring it in during the cold season. That's why nurseries graft them onto hardy rootstock. I suppose that, this can be considered "hydroponics" since the medium is in fact, water. With periodic changing of the water in rooted Cestrum N., I've had them grow in the water for over a year. But they got to be so spindly, though.