Maximum Yield Cannabis Canada 2017 November/December | Page 54
triple c nutrients
The most common causes of copper toxicity are excessive use
of copper sulphate fungicides and industrial activity, such as
mining, that releases copper into the soil.
“
SOME PLANTS BENEFIT from copper
more than others. For example,
sunflowers, lettuce, spinach, beets,
onions, and tomatoes have higher copper
requirements than cabbage, broccoli,
cucumber, mint, peas, and potatoes.”
Copper deficiencies and toxicities are both rare, but they do
happen under certain conditions. A deficiency will present
itself as slow growth, chlorosis, reduced starch formation,
delayed flowering, and sterility. Seeds saved from plants with
copper deficiency will have a hard time germinating. Legumes
will not be able to fix nitrogen as well as they would normally,
leading to chlorosis. The upper portion of broad-leafed plants
will wilt and the top leaves will turn a bluish-green colour.
Copper deficiencies occur most in sandy, alkaline soils. High
alkalinity and waterlogged soil reduce the availability of
copper to plants even if it is present in the soil. Organic matter
that has not been broken down enough will tie up copper until
it is fully decomposed. Excess zinc, nitrogen, and phosphorus
also reduce copper uptake.
The most effective way to fix a copper deficiency is to fix your
soil. Copper’s ideal pH range for proper uptake is 5.5 to 6.5.
Be sure to improve your soil drainage by adding fully decom-
posed organic matter. You may also want to test your soil for
excess zinc, nitrogen, and phosphorus. The quickest fix to
correct this problem is to transplant your sick plants into a
raised bed or container with proper drainage and pH, being
careful not to damage the root system.
Copper toxicity can stunt the growth of your plants and
restrict root growth by burning the root tips. It can reduce seed
germination and lower iron availability. You may not catch
copper toxicity at first because new growth will initially be
greener than normal before plant health starts to decline and
show signs of iron or other micronutrient deficiencies.
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grow cycle
CHROMIUM
Although chromium is a trace element widely distributed in
the soil, you should be aware of potential chromium toxicity in
your garden. In low doses, chromium is an essential element
in human and animal nutrition. However, large quantities can
have devastating effects on humans, animals, and plants.
Although there are a couple of studies from the early 1900s
that found it might be a stimulant for plant growth, there is an
overwhelming amount of evidence that shows it does more
harm than good for your garden.
Chromium is more of a health concern in modern times due
to industrialization. Harmful forms of chromium are used in
industry for plating, alloying, tanning animal hides, textile
dyes and mordents, pigments, ceramic glazes, refractory
bricks, and pressure-treated lumber.
Large amounts of chromium have been found in agricultural
soils due to the use of organic wastes as fertilizers and the
use of waste water for irrigation. Chromium does not degrade
biologically and will remain stable for several months in the
soil without changing its oxidation state.
The most toxic form of chromium, hexavalent chromium, is
easily accumulated by plants. When too much chromium is
absorbed, there will be reduced seed germination, chlorosis,
photosynthetic impairment, and eventually plant death.
If you suspect a high concentration of chromium in your
garden’s soil, it is a good idea to get it tested to be sure. The
2007 Canadian Soil Quality Guidelines for the Protection of
Environmental and Human Health recommends soil should
contain less than 64 milligrams per kilogram (mg/kg) of total
chromium, and 0.4 mg/kg of the form hexavalent chromium.
If you do have high levels of chromium in your soil,
beneficial myccorhizae can ameliorate nutrient deficiencies
caused by chromium toxicity. This also means you should
dig the soil as little as possible so that mycorrhizal colonies
can establish themselves. Your best bet would be not to
grow in that soil at all. Instead, install raised beds with
healthy soil or grow in containers.
Cobalt, copper, and chromium aren’t talked about much
in the gardening world, but they can make or break your
garden. Use this information to correct deficiencies and
toxicities as soon as they occur for healthy, happy plants.