Can you store Copper-Soap solutions?

[Greatgardens]

Are the mixed solutions shelf-stable? I normally use the "Soap Shield" brand. I hope to get down to 5-6 plants total next season, so storing solution would be useful, I think.

[cwavec]

Warning! - don't damage your plants - Read to end.


If anyone reading is a better chemist than I am, please
comment or correct!


I try not to store it. If you mix a solution in a clear container and observe
the color, then observe the color again in a few days, you will see a
change. The blue shade becomes a bit lighter. I also use Soap Shield
but there should be no difference between brands as they are all derived
off a license from a German company.

The question here is whether or not the density of copper ++ ions changes,
and I don't know the answer to that. But Soap Shield (and others) is a 10%
concentrate of copper octanoate in water. This is the product of a reaction
between copper hydroxide and octanoic acid. When mixed with a larger
quantity of water, as in making up a spray solution, this chemical hydrolyzes,
meaning that it separates into free copper ++ ions in solution and an ionized
octanoate fraction.

The copper ++ ions are the important part that does the antifungal work and
having these in maximum concentration is crucial. It seems possible that if
the octanoate portion degrades in storage, some of these copper++ ions
might rebond with it and become less available. I do not know to what
extent but that could explain the slight change in color.

In preference to storing solution, I try to have a properly sized sprayer and to
estimate, as best I can, the final amount required. With a little extra, I can
always spray it somewhere else. This works well for me with a dozen plants.


A couple more points are important here and are largely missed by the community.

Using a spreader-sticker will increase the effectiveness of your copper
solution by orders of magnitude. I have used a product called "Turbo", by
Bonide. It comes in 8 oz. bottles and is very expensive but similar products are
available from Home Depot and Tractor Supply, though they may go by another
name such as "farm surfactant". I currently use (this season) Activator 90
from Lovelace. It's very nice but I didn't save any money.

This combination is a life saver in cases of heavy fungus infestation but you
have to be careful with it as mixing too strong a solution can damage
your plants. I have settled on a maximum concentration of 1/2 oz. of
Soap Shield in a gallon of final spray solution. This will also contain
1/2 oz. of Turbo or other spreader-sticker. 1/2 oz. in the vernacular
is the same as one tablespoon. Usually, I use even less and
find it just as effective, typically 10 or 11 to 12 ml of each in a final gallon.

I think one other suggestion to be appropriate here and that is how to
measure these small amounts, especially if you want smaller
quantities of final solution so you don't have to store it. Trying to pour
out small amounts of these materials into a measuring spoon is a mess,
let alone the question of getting the concentration correct. I now use a
syringe, which I have marked on the side at the proper levels.
Figuring out those levels is made much easier. The syringe need not
have a needle but it's best for it to be big enough.


Hope this helps!

[Greatgardens]

Thanks for a good explanation!

[ddsack]

I got lazy and complacent this summer and didn't spray anything. As a result, my plants are mostly done for the season and I have just a week or two of pickings left. Though our colder nights in September often affect flavor anyway.


I really appreciate your well thought out post and the ideas you provided. Thanks!