On 4/21/2014 12:29 PM, The instructor wrote:
In the professional turf. Industry iron is applied every 4- 6 weeks
how often do you think a household lawn needs it?


It depends upon your soil. Iron tends to be fairly plentiful in most
soils, but its availability to plants is dependent mainly upon soil
pH, and to a lesser degree on the soil temperature and degree of root
development. Before adding a soil amendment, it is always recommended
to have a soil sample tested to determine what, if anything, you need
to add.

Soils with a higher pH tend to tie up more iron in the soil, so
supplementing with iron can be useful. If your soil isn't in the
alkaline range, adding iron may make little to no difference to the
lawn. In the long run, you'd see better results by lowering the soil pH.

Adding an iron supplement to an higher-pH soil through a top-dressing
treatment, such as an iron-supplemented fertilizer, works only for a
few weeks because the added iron will quickly be tied up in the soil.
Thus, if soil conditions require it, it may need to be regularly
applied through the growing season. However, as the soil warms and
bacterial activity and root growth increases, the amount of iron
uptake in plants increases. For that reason, a home owner with an
alkaline soil may be satisfied with limiting iron supplementation to
the spring season.

Tl;dr: don't assume you need to add iron until you have had your soil
tested and have determined its pH.