For trees and large shrubs that are iron deficient,
iron implants can be injected into the trunk or root
flare. It can be as simple as inserting a capsule into
the plant, or may involve a complex network of tubes
delivering the iron. Essentially, iron is released
slowly over time into the sap stream, sending the
needed nutrient throughout the entire plant. The
effects can last for two growing seasons or more
before another injection is required. While there
are do-it-yourself implants containing powdered
iron, this approach is usually only available to
professionals in the plant care industry. Also, given
the expense of a treatment, this is generally reserved
only for valuable specimens or large trees.
Changing the soil pH can also help make more iron
available to plants. Before attempting to do so, however,
it is important to know if high soil pH is indeed the
problem you need to fix. Most garden centers and home
improvement stores carry inexpensive soil pH test
kits. For a nominal fee, most cooperative extensions
perform this service as well. Upon determining that
lowering the soil pH is indeed the correct approach,
granular and powdered forms of iron are available as
pH-lowering amendments. Chelated iron is available in
a dry form and can be spread along the drip line area
of the affected plant. The most common products to use
are elemental sulfur or iron sulfate. Elemental sulfur is
usually much more economical and efficient than iron
sulfate, as it takes about six times more iron sulfate
than elemental sulfur to treat an area. Aluminum sulfate
is also suggested by some as it works faster than either
elemental sulfur or iron sulfate. However, unless your
soil is lacking it, the addition of aluminum will build up
to toxic levels and be detrimental to plant health.
Current wisdom suggests that the only relevant
purpose for aluminum sulfate is to change the color
of some types of hydrangea flowers from pink to blue.
Some other, mostly outdated, literature also suggests
using sulfuric acid to lower a soil’s pH. While it will do
so, it is generally not worth the health risk to handle
sulfuric acid, especially when there are far easier and
less expensive amendments available. Results are
variable, depending on pH and the amendment, and this
procedure may have to be applied on a yearly basis.
“A pla nt lacki ng i ron wi ll show
its defi ci ency fi rst i n th e younger
leaves; i n oth er words, th e new g row t h .”
The only permanent solution to treating iron-deficient
plants in a location that is not suitable for the uptake
of iron is to replace them with a species of plant
that is tolerant of the pH on site. Plant
varieties vary greatly in regards to their
susceptibility to iron deficiency. Some
particularly susceptible plants
include members of the rose family
and ericaceous plants like azaleas,
rhododendrons, kalmia, pieris,
heathers, and blueberries. All other
solutions, even adjusting the soil pH,
are temporary and need to be done
again. Some amendments can adjust the
pH for a few months; others as long as a few
years. Either way, it will have to be done again.
grow cycle
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