On 1/22/2009 11:50 AM, Sleepalot wrote:
"David E. Ross" wrote:

Some 20-25 years ago, I bought a 5 lb bag of zinc sulfate. It was
packed by Bandini, which is no longer in business. I use only a little,
on my four dwarf citrus and on my gardenia. Now that the bag is almost
empty, none of the nurseries around me carry it.
[snip]

From Wikipedia:
http://en.wikipedia.org/wiki/Zinc
Toxicity

Even though zinc is a very essential requirement for a healthy body,
excess zinc can be harmful. Excessive absorption of zinc can also
suppress copper and iron absorption. The free zinc ion in solution is
highly toxic to plants, invertebrates, and even vertebrate fish. The
Free Ion Activity Model (FIAM) is well-established in the literature,
and shows that just micromolar amounts of the free ion kills some
organisms. A recent example showed 6 micromolar killing 93% of all
Daphnia in water.[84]

Zinc sulphate is ZnSO4·7H2O which has a molecular weight of 287.
Zn has a molecular weight of 65, so zinc sulpate is 22.6% Zinc.
So a 5lb bag has 1lb of zinc in it. That seems an awful lot of Zinc
to be adding to your land. How can you be sure you're not poisoning
your land, or the groundwater?

(I am not any kind of expert.)


A lack of zinc causes a blotchy chlorosis in citrus. I've seen this in
my own dwarf citrus (lemon, navel orange, kumquat, and tangelo). I
apply a large pinch of zinc sulfate to each plant about once in three
weeks from late March until the end of September. (See my
http://www.rossde.com/garden/dwarf_citrus.html.)

A lack of zinc causes gardenia flower buds to die and fall off the bush
without ever opening. I've also seen this in my garden.

I apply a large pinch of zinc sulfate to each plant -- along with other
nutrients -- about once in three weeks from late March until the end of
September. I stop feeding my citrus and most other plants in October so
that new growth is not promoted just before we get frost.

Whatever and whenever I give anything to my gardenia I also give it to
my Australian tea tree (Leptospermum laevigatum) to prevent chlorosis.
I give zinc sulfate (about a tablespoon full) to my liquidambar tree (L.
styraciflua), along with gypsum (calcium sulfate, about 2-3 handsful),
elemental sulfur (about 2 handsful), iron sulfate (1 handful), and Epsom
salts (magnesium sulfate, about 2 tablespoonsful) once a year, also to
prevent chlorosis. Both the liquidambar and tea tree show severe
chlorosis -- and even leaf burn -- if I don't do this.

My observations are that the zinc promotes healthy growth in the plants
where I use it. I don't use a lot of it. After all, a 5 lb bag has
lasted me more than 20 years.

I'm not concerned about the ground water in my area. The natural ground
water is so highly mineralized that it can't be used even for
agriculture, let alone for drinking. It was tested during a severe
drought in the late 1970s, with the thought of adding 1 part ground
water to 10 parts imported water in order to stretch the supply of the
latter. Even at that dilution, the result would be unusable.

--
David E. Ross
Climate: California Mediterranean
Sunset Zone: 21 -- interior Santa Monica Mountains with some ocean
influence (USDA 10a, very close to Sunset Zone 19)
Gardening diary at http://www.rossde.com/garden/diary