Georgia Gardener Newsletter Design Tip: February 19, 2009
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A common type of fertilizer
As we get closer to spring, Walter and I are besieged with questions about what to fertilize and when. On top of that we often
get calls and emails about plants that are stressed for a variety of reasons and the first thing most people want to reach
for is a bag of fertilizer. STOP!
Americans are addicted to fertilizers, most of which are synthetically-made
fossil fuel based products. According to the EPA, homeowners use as much
as three times the amount of fertilizer (per acre) as farmers and up to
eight times the amount of pesticides. Homeowner use of garden chemicals
is a significant contributor to non-point source pollution throughout the
Frequent or over-use of fast-acting fertilizers isn't good for the plants and the soil, either. Stimulated by a high dose
of fertilizer, plants can put out green growth too quickly which may be susceptible to insects, disease, drought and
frosts. When using fertilizers, less is best and organic (non fossil fuel) is often the preferred slow way to go.
All fertilizers whether they are synthetic or organic have three numbers separated by dashes somewhere on the label. The
common synthetic fertilizer pictured above is 10-10-10. These numbers are referred to as the NPK content of the fertilizer.
A bag of 10-10-10 fertilizer contains 10% nitrogen (N), 10% phosphorus (P) and 10% potassium (K) which are considered the
macronutrients for most plants to help produce healthy foliage, roots, flowers, fruits and general health.
The remaining 70% of the fertilizer's content can be any number of micronutrients and/or inert ingredients. Milorganite which
is produced from treated sewage has an NPK of 5-2-0.
You may think that using a fertilizer with higher NPK numbers will mean more bang for the buck. However, as the numbers get
higher, the fertilizer can get "hotter" a term we use to mean it can cause chemical burning to various parts of the plant. Many
plants can't absorb that much nutrition quickly so the remainder of the fertilizer is left to run off into nearby waterways.
To be honest, most landscape plants shouldn't require supplemental fertilizer if they have been planted in good soil
that is covered with an organic (not plastic or crumb rubber) mulch. As the organic mulch decomposes, it slowly releases nutrients
back into the soil that are easily absorbed by the plants.
There are a few exceptions. Plants such as annuals, vegetables,
fruit/nut bearing plants,
plants that have been bred to have extremely long bloom seasons or fast foliage growth and plants in containers may need some
supplemental fertilizer to maintain vigor. If planted in good soil, the amount of fertilizer used can be decreased.
I'm a believer in organic fertilizers - those derived from natural sources such as bone meal, blood meal, composted plant
material, cottonseed meal, fish
emulsion, greensand, Milorganite, etc. Their NPK contents may be lower, but they tend to not "overdose" plants with too much nutrition
too quickly. Synthetic fertilizers that have been developed to be slow release (and are usually labeled as such) are better
than the "flash-in-the-pan" quick release fertilizers that have a high NPK.
Holly-tone fertilizer (4-6-4)
Milorganite from treated sewage (5-2-0)
When To Fertilizer...And When Not To
As a general rule, you only want to fertilize when the soil has warmed up and plants are actively growing and
ready to use the nutrients supplied to them. For most plants, that
would be spring through early fall. Some plants like winter annuals and
fescue can be fertilized during warmer periods in the winter. Trees, shrubs,
perennials and warm season annuals should only be fertilized during the
growing season. For warm season turf grasses (bermuda, zoysia, centipede
and St. Augustine) fertilizing should not begin until the grasses have
almost completely greened up in the spring.
Having a detailed
performed every 2-3 years is also a great way to make sure that your soil has the
proper nutrients in the proper concentrations and the soil pH is correct for the plants you're growing. Many plants have
difficulty in obtaining nutrients if the soil is too acidic or alkaline even if the nutrients are present.
Be careful about fertilizing too late in the fall with high nitrogen fertilizers
or plants might be stimulated into a flush of new green growth which can
be damaged during hard frosts. Use of some synthetic fast-release fertilizers
during drought can also have negative effects. Potent fertilizers can stimulate
plants into flushing out with new growth which may cause more water stress
on the plant during dry conditions and some synthetic fertilizers can cause
a build up of certain salts in the soil which can actually pull water back
from plant roots. And finally, unless a plant is clearly suffering from
a nutrient-deficient problem, do NOT apply fertilizer to stressed plants
until the problem has been identified. Fertilizer can't compensate for
compacted soil, poor drainage, inadequate mulch, improper light, insects
and certain diseases.
Remember, less is best and always read the fertilizer label carefully.
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