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How To Read A Fertilizer Bag

Do I need to fertilize my plants?

Do I need to fertilize my plants?  That can be a complicated question.  Since I hate the complicated questions, I thought it would be great to break it down to the basics.

what kind of fertilizer to use

What do plants need to grow?

That is a question that you always need to keep in mind whenever you think about doing anything with your plants.

The truth is your plants need only water, air, light, and nutrients.

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So let talk about nutrients!  And whenever you talk about nutrients we also talk about water.

Does water add nutrients to my plant?

Plants use water much the same way we use water.  Both use water to help more nutrients thru to the cells.

To get into technical, the process of water moving thru the plant is called “translocation”.  Without effective translocation, nutrients can’t get to the plant cells.

So before you worry about adding nutrients make sure that you have been properly watering your plants.

What kind of nutrients/fertilizer does a plant need?

The 3 most important nutrients that your plants need they can only get from the soil; nitrogen, phosphorus, and potassium.

There are also other nutrients that are critical for a healthy plant.  These include calcium, sulfur, magnesium, and other trace elements.


Doesn’t the soil have nutrients naturally?

Yes.  Soil is made up of many of these nutrients.  The problem you have as a gardener is that you can not tell by looking if your soil has the right balance of nutrients.  The easy solution to finding out what base you are starting with is to have your soil tested.  Many state universities offer free soil testing.  Check with yours to find out the requirements.

Potting soil

There are a vast number of potting soils on the market.  Some of these are plant-type specific.  They give you the levels of nutrients that your specific potted plants need.  Check out more about potting soil by reading Organic vs non Organic Potting Soil

If you are using last year’s or used potting soil you need to understand your starting point so testing the soil is a great idea.

Why would I need to fertilize my plants?

Even your potted plants may need more than what the soil contains.  Whether it’s general potting soil or “used” potting soil you may need to boost the nutrient level.

Outdoor gardens often need to have the soil enriched with additional nutrients.  Seldom will the perfect level of nutrients be present.  If you garden year after year in the same area you will almost certainly need to add nutrients.

How do you read a fertilizer label?

There are 3 letters on every fertilizer product.  Each of these letters represents the 3 important nutrients that your plant needs; N for nitrogen, P for phosphorus, and K for potassium

So that means that a fertilizer that says 16-8-12 contains 16% nitrogen, 8% phosphorus, and 12% potassium.  The remaining container is made up of fillers.

how to read a fertilizer bag

What does each part of fertilizer do for my plants?

N or nitrogen is important to grow rich green leaves.  Nitrogen is vital for the plant to convert sunlight to sugars ….photosynthesis.

P or phosphorus helps form new roots, grow seeds, fruit and flowers.  Without the right amount of phosphorus available your plants may grow big and green but may not produce good fruits or flowers.

K or potassium helps grow strong stems.  It also helps overall balanced growth and some disease control.  Potassium helps water and other nutrients to move thru the tissue of the plants.  Without adequate potassium plants become weak and the growth will be stunted.

When should I fertilize my plants?  How often?

To have the healthiest plants you can the best thing to do is to understand your starting point.  Either has your soil tested or start with fresh potting soil labeled with nutrient levels.

fertilizer understanding basics

When you decide what plants you want to grow make sure you have an understanding of the nutrient need of that plant.  Some plants need a larger amount of N, P, or K

For example

Tomatoes will need a nice balanced fertilizer when young.  a 10-10-10 would be fine.  However, as the plant starts to produce fruit you would have a better harvest if you give the plant access to a higher amount of P.

Lettuce and other greens would do best with a fertilizer that is higher in N for nice green leaves.  They will need less P.  So a 5-10-5  would be fine

A general principle to follow when you are in doubt is:

  • great leaves then more N,
  • great flowers and fruit than more P,
  • large strong plants or potted trees then more K

So how do I need to fertilize my plants?

I have a great video on my favorite kind of fertilizer.  Check out how to make compost tea from worm castings

It is best to set a regular fertilizer schedule.  I like to give all my plants a little fertilizer once a month.  A schedule like this will give your plants a consistent feeding of fresh nutrients.

If your plants show signs of distress it is best to act quickly to limit any damage.

For instance, if your plants start to show yellow leaves or light green leaves you will need to add more N to your soil.  If your flowers are small or don’t open then add some P as soon as possible.  If the stems of your plant seem too weak to hold up the leaves or the plant seems small and thin then add some K right away.

You may have great organic fertilizer right in your kitchen!  Read DIY organic fertilizer to find out how to fertilize your plants from ordinary things

If you grow using hydroponics read “hydroponic fertilizer”


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Follow these basics and you will have a great start to a rich healthy garden.

Please share, like, and comment.  I really appreciate it!


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