Question

What is the best fertilizer this time of year for Denver, CO weather?

Asked by William Owen
Brighton, CO

I've been using Richlawn for a few years but it's not doing so well now.

Answer

Richard Heller

Answered by Richard Heller

New Rochelle, NY

Greener by Design

October 19, 2012

The chances are it's not a problem with your fertilizer, but a problem with your soil acidity.

All plants have different needs when it comes to feeding, and the plant's ability to absorb nutrients is dependent on soil conditions, not just what you put in the soil.

  • Soil nutrient content and acidity change over time. 
  • In many ways acidity is more important than nutrient content.

Oddly, soil testing is both the most useful and most ignored tool in the gardeners tool box. Each plant has a very specific acidity range it prefers. Evergreens for example prefer acid soil, while deciduous plants generally prefer alkaline soil. If the pH range in the soil is outside of the range of the plant, the plant will not be able to feed.

Go to http://en.wikipedia.org/wiki/Soil_pH for more info on acidity.

Test the soil first

Basically you can hammer the plant with nitrogen and it will not be able to absorb it as long as the pH is off. Even if the pH is correct, fertilizing plants without knowing what nutrients are already in the soil means there is a good chance you wont get all the nutrient needs of the plant met.

  • For example, soil may be very low in phosphorous and high in potassium.
  • If your fertilizer is not low in potassium and high in phosphorous you will only make the imbalance worse.

So first, test the soil and focus on the pH and N,P,K (nitrogen, phosphorous, potassium) levels. To learn more about N,P,K and fertilizer go here

Then add soil amendments

Next amend the soil for the pH first and fertilizer second. Fall is the time to amend pH and it takes months to move the acidity over to where it needs to be. 

For more info on adjusting soil pH go here.

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