Yes, roots need air (oxygen). Water uptake, and therefore nutrient uptake, are energy driven. In order for the process to occur, plants need to torn the food they make into energy, and that requires oxygen, just as your own body requires oxygen to keep your cells fueled. The reason many terrestrial plants can be grown in water is by virtue of the fact they can change root structure. The roots produced in water are quite different from those produced in a soil-like or highly aerated medium (perlite - screened Turface - calcined DE - seed starting mix, e.g.). Physiologically, you will find these (water) roots to be much more brittle than normal roots due to a much higher percentage of aerenchyma (a tissue with a greater percentage of intercellular air spaces than normal parenchyma - as in terrestrial plants). Aerenchyma tissue is filled with airy compartments. It usually forms in already rooted plants as a result of highly selective cell death and dissolution in the root cortex in response to hypoxic conditions in the rhizosphere (root zone). There are 2 types of aerenchymous tissue. One type is formed by cell differentiation and subsequent collapse, and the other type is formed by cell separation without collapse ( as in water-rooted plants). In both cases, the long continuous air spaces allow diffusion of oxygen (and probably ethylene) from the upper part of the plant to roots that would normally be unavailable to plants with roots growing in hypoxic media. In fresh cuttings placed in water, aerenchymous tissue forms due to the same hypoxic conditions w/o cell death & dissolution. Note too, that under hypoxic (airless - low O2 levels) conditions, ethylene is necessary for aerenchyma to form. This parallels the fact that low oxygen concentrations, as found in water rooting, generally stimulate plants to produce ethylene. For a long while it was believed that high levels of ethylene stimulate adventitious root formation, but lots of recent research proves the reverse to be true. Under hypoxic conditions, like submergence in water, ethylene actually slows down adventitious root formation and elongation. Soggy soils are hard on plants for a couple of reasons. A) Roots can't quickly make back and forth transitions from well-aerated to hypoxic. B) Soggy soils don't allow the roots enough O2 to work efficiently, so root function is impaired or roots die from a lack of O2. C) Gas exchange in soggy soils is poor. O2 diffuses in air about 10,000 times faster than in water, so in transitional situations (aerated to hypoxic) the plant can't get O2 from the soil OR the upper plant organs. Also, since CO2 is heavier than air, soils with poor gas exchange tend to fill with CO2, and hold onto gas byproducts of decomposition - like the CO2 already mentioned, sulfurous gasses, methane ... which is an obvious problem. Al

PW - Thanks for the kind words! also PPE - I received your recent message. I've been very busy with spring pruning/ repotting, which is why I haven't yet expressed my gratitude, but I will. Thank you - I was moved! Is there any downside to starting the layer via ringing method up to a year before I plan to prune + pot the propagule? There is no question things will move along much faster if the layering takes place with the plant outdoors, but you can start the layer a month or so before you expect to move it outdoors, which can be done A) when nights are reliably above 55*F, or B) by moving the plant in and out as temperatures allow (should be above 55*). Is it okay to keep it on over the winter? It depends on where the layer is located on the plant. Since you'll be cutting through the phloem tissue, you'll be cutting off flow of photosynthate from all foliage distal to the layer to roots. So, if the layer is on the main stem proximal to all foliage, there is a very good chance that the plant's root system could die; however, if you are layering the main stem distal to other branches on the stem, it wouldn't be a problem. It's best to start preparing for the layer in early to mid-spring and plan on separating the layer in mid to late summer. Faster is better because it decreases the probability of a fungal pathogen gumming up the plumbing before new roots have an opportunity to form a connection to the propagule's existing vasculature. Does layering on the main stem of a plant have any effect on the growth rate above? Yes. How much, depends on what fraction of the flow of photosynthate (food) is being cut off by the layer. If you have 10 branches below the layer on a main stem, it won't have much impact on growth rate. If you are air layering the main stem at a point proximal to all, the effect on growth rate would be greater. In any case, the reduction in growth rate should be temporal; this, because the layer also blocks the polar flow of auxin (it moves from shoots to roots only). With the flow of auxin reduced to almost nil, auxin's inhibitory effect on new lateral branching will be almost entirely eliminated (in apically dominant plants), so foliage on the new branches will start to provide a net return on energy outlay when the first of the new leaves are about 75% mature. Al

If you'll look at the power supply fan on the back of a desktop computer, you'll see what's wrong here. The blades are surrounded by a round hole in the fan body, just slightly larger than the blade diameter. They're made this way because a fan that's trying to "pump" or mov air from one area to another works best when it's surrounded by a baffle. Well, your tray ceiling is acting as a loose baffle. The fan tries to pump air from above, but it's mainly pulling air from (effectively) a closed box. That's why it moves less air than it should - there just isn't much in that little box behind it. So, the solution is to lower the fan until you get the breeze you're seeking.

Many succulents grow air roots. Sometimes because they are thirsty; sometimes because it is quite humid; sometimes because that is how they grow. In general, it isn't a problem. I usually leave them alone, and they eventually dry up. Sometimes I cut them off. Most of the time I don't bother. It doesn't mean you need to cut the plant. If you did, they often 'turn' into soil roots. Most succulents are summer growers, and winter dormant. They could totally stop growing, but usually it is warm indoors and they continue growing, but slower than during their active growth period. Keep it in good light. If light is not enough, pads could grow skinny, and weaker than they should be. If there is a pad you don't like, you could cut it off and re-root the cutting. Best time to do that is during their active period.