Understanding Fertilizer

Common Fertilizer Questions Answered

Understanding how and why to fertilize can be intimidating to home gardeners.  Add those three little numbers into the mix and one can be easily overwhelmed and confused.  Fertilizing doesn’t have to be confusing though.  And no, you don’t have to be a scientist or chemist to understand it.  At least not the basics…

Here are answers to some common questions:

What do the numbers mean?
Nitrogen, Phosphorus and Potassium (N,P,K) are what the three numbers on the fertilizer package refer to.  The numbers show the percentage of each component in the bag of fertilizer with the remaining product being inert ingredients or filler.What do these chemicals do and how do I choose the right one for my project?
The easiest way to remember what each of these chemicals do is to remember ‘Up, Down and all Around’.

Nitrogen:  (Up)  The first chemical listed helps plant growth above ground and produces leafy green foliage.  If you want to green up your lawn or a plant, you would look for a fertilizer that has a high first number.

Phosphorus:  (Down)  Phosphorus is the second number listed and works on establishing root systems.  This is also the key component for producing flowers and fruit.  If you want to help your flowers bloom, pick a fertilizer that has a high middle number.  Many of these fertilizers will be labeled for blooming and fruiting.

Potassium:  (All Around)  The final number works on the overall health of the plant by building strong cells within the plant.  Potassium helps plants withstand various stresses such as extreme cold, drought and also helps to fight diseases and insects.

What kind of fertilizer should I use?
Many fertilizers today will tell you what they are best used for; tree and shrub, flowering or evergreen.  If you can’t find exactly what you are looking for, choose a fertilizer that is considered all-purpose such as 10-10-10.

Two kinds of fertilizers are easily available:  Fast-release and Slow-release
Fast-release – These allow the nutrients to be readily available to the plants.  As a     result, the nutrients may leach quickly through the soil allowing for runoff.

Slow-release – These release the nutrients gradually, therefore they are less likely to leach out of the soil and the plant is able to take advantage of all the nutrients instead of just a small percentage.  These are a great choice in areas where the potential for runoff is very high such as slopes or compacted soils, especially if you live near a water source.  Many organic fertilizers fall in the slow-release category.

How much do I use and how do I apply it?
How much you use will depend on the type of fertilizer you are using and what you are fertilizing.  Be sure to read the label for application rates.   If you are still unsure, remember that more is not better as you could burn the plant.

The manner in which you apply it will also depend on the form of fertilizer you purchased.  Granule will be spread on the ground and loosely worked in while fertilizer stakes will be placed in the ground.  The one thing that is consistent between the types is to apply the fertilizer at the drip line.  The drip line is at the edge of the tree / shrub canopy.

When is the best time to fertilize?
Most trees and shrubs experience a single flush of growth in the spring followed by slower growth throughout the summer and fall.  Therefore the most desirable time to fertilize your trees and shrubs is in the early spring just before they begin to grow.  This allows the plant to use the nutrients in the fertilizer to its best advantage when it is vigorously growing.

If a plant has been under stress or is showing signs which might indicate a nutrient deficiency, then a light fertilizer application can be made at any time during the growing season.  However, you should avoid fertilizing trees and shrubs when conditions are dry especially if you are unable to provide adequate water soon after the fertilization.  Lack of water after fertilizing could result in the salts from the fertilizer building up and potentially damaging the plant’s root system.

Fertilizing in the early fall is not recommended.  Fertilizing at that time could stimulate new growth when the trees and shrubs need to lose their leaves and go dormant.  If you want to fertilize in the fall, wait until the plants are dormant and just before the ground freezes.