[Arid_gardener] Lady Banksia problem

[Dick]

To add a little of what I've learned from Terry Mikel an others, if my memory serves me well, consider the following: Water--H20, has the ability to become a vapor at rather low temperatures and return to a liquid state unaltered when it returns to that temperature. Higher or lower pressure will raise or lower the rate and temperture at which the water moves to or from the vapor phase. For example, your car radiator will not boil even though the temperature may be well above the 212 degree boiling point because it is under pressure. Make the mistake of removing that cap, however, and you run the risk of being scalded as that super heated water instantly turns to steam and spews out like a miniature volcano.

In a plant vascular system, the feeder roots take up the water that is channelled up through the stem vascular system at a rate equal to the rate of transpiration from its foliage.. As the supply of water to feeder roots in the root zone dwindles, , wilt begans to set in and, if water is not soon replenished, the wilt procedes to the point of no recovery and the affected foliage dies.  

The water carries all its load of soluable minerals and salts along with it to the tip of its leaves packing them into the individual cells. The water turns into a vapor and transpires through the leaf stomata into the atmosphere. 

Its mineral load, unable to evaporate, packs into cells. When the cell is packed full and can't function, it dies (turns brown); we call it salt burn. At some point, the accummulation is critical and the leaf falls. The more "salt burn" the plant suffers, the less its ability to produce carbohydrates. Without the capacity to process its own food, the plant dies. Some plants can tolerate salt better than others but I have no idea why. 

Frequent shallow irrigation and surface evaporation cycles leave behind the entire load of salts and other minerals in the water. These higher and higher concentrations are picked up by feeder roots.  Over time, the salt accumulation showing up as that ugly brown fringe creaping down the leaf, is reducing the function of one of a plants vital organs, its foliage, without which it cannot exist. The more salt accummulated in the root zone,  heavier the load carried to the foliage accellerating the speed at which cells are packed with salt and killed.

The average salt content of our water is, if my memory serves me this moment, 8.5 wt. percent. Most plants can live with that. The purpose of flush irrigation is to flush the previously deposited salt load beyond reach of the feeder roots replacing it with another 8.5 charge so that the water adsorbed by feeder roots never excedes 8.5 or the load in fresh water.

The most effective irrigation I have found is the frequent use of an overhead oscillating sprinkler. My yard configuration now makes that extremely difficult and messy and I have stopped the practice.

I believe my crude "science" here is fairly accurate but, if the function of this forum is purely educational as I percieve it to be, I would welcome any adjustments or friendly contradictions of what I have believed are facts.  
  ----- Original Message ----- 
  From: Steve Sheard 
  To: Bill Woody ; arid_gardener at CALS.arizona.edu 
  Sent: Monday, July 09, 2007 8:31 PM
  Subject: Re: [Arid_gardener] Lady Banksia problem


  Dear Bill,
  There are not many roses that are not being affected by our +115 temperatures. Most of the browning on roses at this time of year is not from mildew or rust (I have yet to see rust in the valley). My guess is that the browning is from "salt burn" due to a high concentration of salts in the soil and maybe the bush not getting enough water. 
  To reduce the salts you need to throughly soak the bed to wash the salts down below the root zone, and then leave it a day or two to dry. Dig down and see how wet it is.
  I am watering my roses every day with these very high temperatures. When they drop back to 110 F I will go back to every second day. A rose on the east side should need about 4 gallons at a watering. 
  Visit http://www.roses4az-mevrs.org/ for more info on growing roses in the valley.

  Regards
  Steve Sheard
  (Not a Master Gardener, A consulting rosarian with ARS)


  ----- Original Message ----
  From: Bill Woody <billw-9 at msn.com>
  To: arid_gardener at CALS.arizona.edu
  Sent: Monday, July 9, 2007 7:47:17 PM
  Subject: [Arid_gardener] Lady Banksia problem


  Our Lady Banksia vines are getting browner.  They are growing on trellises on the east side of a concrete block wall so they are shaded after about 1 pm.  I have sprayed them with a dilute solution of baking soda and soap to kill mildew and stop rust but they continue to decline.    Might they need shading for a good portion of the morning as well in this fierce heat?  Or what do you experts suggest?

  Bill Woody


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