What do those numbers mean?

Rhodo 1.8kg

N-P-K, that mysterious formula.  What does it all mean?  Trust me; you’re not the only one who gets confused by those numbers on fertilizer bottles.  In fact, I’d say you’re in the majority so don’t be shy when you’re looking for the right food for your plant as it’s important to get the proper fertilizer for what you’re growing.

However, don’t get caught up in getting the EXACT formulation that you read about on some web page from Kentucky or England or wherever.  That specific fertilizer may not be available here and really, you don’t have to match the numbers.  Every major brand comes up with their own N-P-K rating on fertilizers.  What is most important is what the fertilizer is made for.

N-P-K is basically the percentage by weight of the material in fertilizer.  The numbers won’t add up to be 100% as there are other elements that make up the product such as minerals and fillers (so that the concentrated fertilizers don’t ‘burn’).  You might think that someone didn’t do their math right but that isn’t the case.

N stands for nitrogen.  It helps to make things green and promotes foliage growth.  For example, high nitrogen lawn fertilizer is used in the summer to keep the grass green as it’s all about the top growth at that time.  Through the winter you work on what’s going on under the ground with a lower first number.

P stands for Phosphorus which promotes good root growth along with fruit and flower production.  Typically hanging basket and annual fertilizers have a high middle number for flowers.

K stands for Potassium which is good for all around plant health.  An easy way to remember what N-P-K stands for is this saying: “Up (N), down (P) and all around (K).”

While there are a lot of well-known brands out there it doesn’t always mean they have a great product.   When you think of fertilizers what brand automatically comes to your mind?   Big money goes behind the marketing of some brands and you’re tempted to run out and buy whatever a well-known name is paid to tell you to buy in a commercial.  I wish I had that power.

I’m not here to promote one brand of fertilizer over another.  I just want you to think about what you’re buying fertilizer for and what is important to that particular type of plant at that particular time.

Synthetic (chemical) fertilizers are like fast food to plants.  The N-P-K numbers are generally quite high as opposed to organic fertilizers which are low.  Many people tend to bypass the organics because of the low numbers.   To be honest, the lower ones in organic options are much better for your plants in the garden, in my opinion.

Organic fertilizer is naturally slow releasing, meaning the food is available to your plants for a longer period of time and doesn’t instantly dissolve and run off into the groundwater.  Organic fertilizer can also act as a soil amendment that will improve your soil over time. What it is made up of is natural, good for the garden and doesn’t damage microorganism or earthworm activity.

I use synthetic or partially synthetic fertilizers in annual containers because the plants are done by fall.  Annuals live life in the fast lane and want their food the same way.  Typically a chemical fertilizer for annuals is high in the middle number for flower development.

Again, there are a lot of different formulations out there with all sorts of numbers.  Choose a fertilizer that is specific to the type of plant.   If you’re growing roses then buy a rose fertilizer, palm trees go with a tropical or an evergreen food, rhododendrons get fertilizer specific to rhodos, etc.  Don’t get too caught up in the numbers game, the fertilizer companies have already figured that out for you.  If in doubt, just ask us, we’d be happy to help!

Shirley Eppler

June 2013