cattleya leaf tip necrosis

[lschalkwyk]

I have a Cattleya that I bought as a bare root plantlet almost 5 years ago. It has taken a long time to get going, but is now growing well and sending its first flower shoot. It was probably too dry and underfed in previous years, because it (along with my phals) has responded very well to finer bark medium and a heavier feeding regime. I'm now using 200 ppm N in a weekly soak with made with a 20-20-20 + trace elements fertiliser.

One of the Cattleya's leaves is black at the tip and it's progressing. There is now maybe

15 mm of dry black leaf at the tip and then a band of chlorosis of 3 or 4 mm wide. Can anyone offer an educated gues on whether this is due to salinity, lack of Ca, a virus, or something else? The fertiliser I'm using doesn't contain Ca, but the water is very hard, containing an average of 276 ppm of total hardness as CaCO3 according to the water company.

Leo

[Duncan Vincent]

The calcium found in water is almost totally unabsorbable by plants(or humans for that matter). Makes my blood boil every time i see a tums commercial telling people that it "contains calcium that your body needs". Calcium nitrate is very readily absorbed and is very cheap.

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[dbs]

That's the general rule that we were taught in General Chemistry ISTR. But, if memory serves, covalently bonded chemicals tend to be insoluble unless they have an uneven charge distribution spatially. Alcohols are an interesting group that dissolves but doesn't dissociate due to the hydroxyl group that introduces a spatial charge disparity.

My previous example of sucrose is an interesting exception to that rule because they will dissociate upon heating. Brewers use the fact that sucrose hydrolyzes to produce an invert sugar that has better fermentation properties (though an acid is usually employed as a catalyst). Cooks also "invert" sucrose by an addition of corn syrup (aka fructose) while heating a sucrose solution to prevent crystalization during cooling.

Dave