On 10/7/11 7:12 AM, Bob F wrote:
David Hare-Scott wrote:
Bob F wrote:
I've just been told that the curled under leaves on my italian prune
trees are caused by magnesiom deficiency and I should apply a few
pounds of epson salts under each tree.

Is the diagnosis likely to be accurate? Location is Seattle.


I don't know about leaves curling, I thought magnesium deficiency
cause leaf yellowing especially in older leaves. Can you provide a
photo?

Photo here (I hope)
http://www.flickr.com/photos/68364065@N07/6220401824/


What kind of store wound I go to for a good price on 50 or 100 lb
bags of epson salt?

A few pounds per tree seems quite excessive to me, this is a trace
element not a major nutrient. If you over-do it you won't have a
problem with curling leaves 'cause you wont have any leaves at all. Another
problem is that epson salts is very soluble and unless it
binds to humus or clay colloids it will leach out quickly.

Here is another method that may be work if it is Mg deficiency. Treat some (or
all) trees with a foliar spray of epson salts,
possibly repeated in a week, if it is Mg deficiency they will recover
quite quickly, that is within weeks. For the longer term treat with
dolomite which will slow release Mg over time.

Another possibility is that the soil is very acid which tends to lock
up some minerals like Mg so liming or adding dolomite will raise the
pH and release Mg. A dye-indicator to test pH is cheap and
sufficiently accurate for gardening and can be used in many
situations.
Acid soil is common here in Seattle I believe, and it's been a long time since I
limed the lawn, so maybe that's a better idea

Epsom salts are acidic -- magnesium sulfate. If acidic soil is your
problem, this will only make it worse.

In any case, insufficient magnesium in the soil requires only a small
dose to correct. I put about 2 tabslespoonsful around each rose bush in
my garden only once a year. For roses, magnesium promotes the sprouting
of new canes. I corrected chlorosis in an Australian tea tree
(Leptospermum laevigatum) with a half-handful of Epsom salts without
ever repeating the dose; I merely continue to feed the tea tree with
acidic fertilizer (ammonium sulfate).

I buy Epsom salts at a local drug store. A small carton (about the size
of a half-pint of milk) lasts several years.

--
David E. Ross
Climate: California Mediterranean, see
http://www.rossde.com/garden/climate.html
Gardening diary at http://www.rossde.com/garden/diary