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As young plants re-establish in the field or garden, they often have
trouble taking up the nutrients they need from the
soil. Soil conditions
such as high pH, excess moisture, and cold temperatures also can make
nutrients unavailable to plant roots. This is often exhibited by
purpling or yellowing of the lower leaves on plants. When this occurs,
foliar feeding spraying liquid fertilizer on the plants' leaves and
stems may provide needed nutrients for a short period of time until the
roots can resume nutrient uptake.
Foliar feeding has many other
reported applications: It can be used at flowering to increase fruit
set. It is believed to make plants less sensitive to frost. Foliar
sprays of compost tea help prevent plant diseases. And certain
nutrient-related problems can be addressed by foliar sprays of the
specific nutrient, such as calcium to prevent blossom end rot on
pathway for nutrient uptake in fruits and vegetables is by the roots, so
do not expect foliar feeding to supply all the nutrients needed.
Remember the motto of sustainable farming is "Feed the soil, not the
plant." Foliar feeding is a temporary measure for special situations,
and should not replace cover cropping and soil amendments as recommended
by regular soil tests.
Foliar fertilizers should be diluted so
as not to burn the leaves. Fish emulsion and seaweed are the preferred
foliar fertilizers for vegetables. Not only are they easy to dilute,
they also contain micronutrients that are essential to plant health.
a foliar fertilizer by a fine mist sprayer or nozzle. Spray to the
point of run-off.
Mix the foliar feed solution in a clean
sprayer. When you're done, run plenty of clean water through the sprayer
to prevent clogging.
Foliar feed on a cloudy day (but not if
rain is imminent), early in the morning or late in the afternoon, to
avoid sun damage to the wet leaves. Do not foliar feed on hot days, as
the heat can cause plants' stomata to close and prevent absorption of
If in doubt about the success of foliar feeding,
use a refractometer. Take a sample before foliar feeding, and then a few
minutes after foliar feeding. If the Brix has increased, the plant has
taken up the nutrients.
Water-soluble fertilizers can be applied
through an irrigation system, a process known as fertigation. Not only
does fertigation save time, it also ensures a more even and effective
distribution of fertilizer directly to the plants' roots. Like foliar
feeding, fertigation can be used to quickly fortify plants that are
under stress and unable to take up nutrients from the soil.
Fertigation requires a system for injecting the
fertilizer into irrigation water at the correct rate. The simplest
solution is to use a Syphonject, which attaches between a garden hose
and faucet and has a suction tube that is placed in a bucket of liquid
fertilizer solution. The Syphonject draws up fertilizer and mixes it
with water at a rate of 16:1. It is suitable for watering with a hose,
but not with drip irrigation. For drip irrigation, a fertilizer injector
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from JSS Advantage May 2010