I've wondered about this question too. With ordinary plants in potting soil, the risk of over-fertilizing is that as the water in the soil is taken up by the plant or evaporates, the concentration of fertilizer salts can increase greatly. At some point the osmotic pressure of the water and fertilizer surrounding the roots can interfere with water uptake by the roots and possibly damage the roots. With mounted orchids though, I haven't seen any information on what happens physiologically when watering with fertilizer. It seems three things are going on: (1) the roots are absorbing water into the velamen, (2) the roots are absorbing fertilizer ions, and (3) water is evaporating into the surrounding air. I would assume that you would want all of the fertilizer to be absorbed before all of the water on the surface of the roots is gone. Otherwise there would be a thin, dry coating of all the residual fertilizer on the roots. So the question is how fast roots can absorb fertilizer - anyone know? It would seem that for that reason, it would be bad to use any fertilizer at all when the air is warm and dry, since the water on the roots would evaporate too fast.

I found an absolutely beautiful Jade in a dumpster when I was tossing my trash. I pulled it out and after trimming a bit it was absolutely fantastic. I proceeded to over water it and practically kill it. It got so bad that I thought it was a goner...and then I did the unthinkable. I cut off the entire matted and ruined root ball. The whole thing. I let it air a few days and stuck it in an awful mixture of street dirt. 6-months later, it is making a huge comeback. I barely water it now and give it a shower every six weeks or so to blow away any mites or whatever crawlies happen on it. It is doing fine. I happened on another specimen with an 8-inch trunk and I broke it up to make about 5 new plants with 4-inch trunks (the 8-inch was rotting). I'm hoping to get at least 3 of those rooted using the same method. Re-rooting a 4-inch trunk gave me some confidence with Jades. They seem to be really resilient if you sorta be a little mean to them ;-)

High nitrogen can hurt root and flowering ability in cotoneaster plant. See excerpt from below link: http://www.sciencedirect.com/science/article/pii/0304423881900649 " Although root growth was not increased by either Nitrogen or Phosphorus, high N levels inhibited root growth." More link to show that too much phosphorus can hurt root & flowering: https://laidbackgardener.wordpress.com/2016/05/18/the-myth-of-starter-fertilizers/ "further studies showed that large quantities of phosphorous were not necessary for rooting. Yes, the soil must contain a small amount of phosphorus in order to stimulate rooting… but that’s also true of any other nutrient. If the soil totally lacks nitrogen, zinc or iron, that too will hamper rooting. In fact, plants actually root poorly in soils excessively rich in phosphorous. You’re far more likely to kill plant roots with 10-52-10 fertilizer than to stimulate their growth. " http://davesgarden.com/guides/articles/view/3788/ " When plants are grown in low phosphorus environments they emit organic acids from their root tips. These acids allow mycorrhizal fungi to penetrate the roots and form the networks that assist roots in absorbing water and nutrients. If the phosphorus levels are too high the roots do not emit the acid and the mycorrhizal networks do not form. This forces the plant to put more effort into root growth to compensate for the lack of mycorrhizae." U. of Colorado Extension has excellent info. on Organic fertilizers: "recent CSU research has shown that phosphorus from bone meal at NPK 3-15-0 is only available to plants in soils that have a pH below 7.0." On rock phosphate: Recent CSU research results concluded that no rock P (regardless of mesh size) is available for plant use unless the soil pH is below 7.0. http://www.ext.colostate.edu/mg/gardennotes/234.html According to CSU, Kelp powder has NPK of 1-0-4, decent potassium, plus trace elements, only need 1/4 to 1/2 teaspoon per gallon, due to its high salt. **** From Straw: I tested bone-meal many times, with negative result in my soil pH near 8. 1) killed over a dozen geraniums by topping with bone-meal in hot summer .. that burnt their roots, but their colors were vivid at first. 2) put bone-meal in the planting hole of Sharifa Asma, the color DID NOT deepen, but really wimpy root, plus the soil got hardened. 3) Killed a $30 gallica rose gifted by a friend with bone-meal in the planting hole. 4) Made Crimson glory really wimpy by putting bone meal in the planting hole. 5) Made wimpy Yves-pink-seedling into a Black-spot fest by moving it, then put bone-meal in the planting hole. CONCLUSION: phosphorus is best in small amount as in 1/10 of potassium in rose-tissue analysis done by U. of CA at Davis. Phosphorus is best AS soluble, as in leaves, manure. Chicken manure at NPK 5-3-2 has plenty of phosphorus, plus trace elements zinc, copper, and boron.

I think it's disingenuous to suggest that a well-made 5:1:1 mix needs constant watering. It doesn't. Even the gritty mix, that holds even less water than the 5:1:1 mix doesn't need constant watering. Do you have to water more often than more water-retentive mixes? Yes. But there is a price to be paid in the form of lost potential for the convenience of soils that hold water for extended intervals. Denise: there is a monetary consideration that clearly delineates hobby growers from professional growers. Nursery/greenhouse ops wouldn't be willing to pay employees to water twice as often as a heavier mix because they've weighed the cost of limitations due to temporary periods of excess water retention against the cost of watering more frequently, and decided it's to the advantage of their bottom line to sacrifice some lost potential to save labor $. The hobby grower is in the hobby to scratch their nurturing gene. for the most part, They actually feel good about spending more time with their plants and offering them the best care they can afford, as opposed perhaps to the cheapest soil they can find. Think of it in terms of the difference in perspectives between a puppy mill and the owner of a new puppy - two completely different worlds. So, care given by a nursery and greenhouse of will always be in consideration of the bottom line, which means following their lead will not always be in the best interest of the plant. Your care and mine are far more likely to be about providing the best care we can. Holding up the practices of a greenhouse or nursery is a little like asking us to emulate a puppy mill. I know - tugging at your heart strings. I wasn't really trying to do that - just the first good comparison that popped into my mind. Chicken farmer/ pet chicken, beef grower/ pet cow is another. If a plant is properly handled during a repotting session, it would be extremely unusual to lose a plant. Look at the two following root reductions where well over 90% of the roots were removed:Here, I have just finished pruning the top. This is after the root work was completed: Here ^^^, about 1/2 of the roots have already been removed The plant with root work complete:Note the size of the roots I removed. Many were more than 1" in diameter. In subsequent repots, I have removed all the knobby roots from the bottom of the bole. This plant was grown in the gritty mix - note the remarkably (for a maple) fibrous root system. The entire soil mass, you can see, is densely packed with the fine roots that do the lion's share of the work. After the root work: If you look, you can see the wire that shows this tree was layered above a poorly formed (but not unhealthy) root system. Where each of the 7 main roots are now, those that emanate horizontally from the trunk, I bored 7 holes into the sapwood and treated each hole individually with IBA rooting gel. I ended up with 7 perfectly spaced roots that will look great when they are later exposed on top of the soil. One more series, just to illustrate how little trees care about having half or more of their root systems removed: Again - note how healthy the roots are. ^^^ I wouldn't suggest you approach root pruning this radically, but removing 1/3 to 1/2 of a young plant's roots (younger than say 25 years) should be no problem. Plants that grow extremely fibrous roots (boxwood, azalea .....) need a slightly different approach. Keep the roots always wet while you work. First remove all problem roots (crossing, encircling, girdling, j-hooked roots - roots that grow upward, straight down, and roots that grow back toward the center of the root mass. After the problems are corrected (makes future repots much easier - the first is always the hardest) concentrate on removing the largest roots with the fewest fine roots attached. We know that root congestion negatively impacts growth, vitality (health) and yields, and those limitation become increasingly severe as root congestion increases. Pruning a bit around the edges of the root/soil mass and potting up is a half measure that ensures limitations remain until someone physically gets into the root mass and corrects the congestion and problem roots. Even planting out (in the landscape) will not eliminate the effects of congestion in the soil mass that existed at plant-out time. Al