Monday, January 17, 2011

Don't Overfeed Your Plants, Warn the Garden Professors

One of my favorite blogs to follow is "The Garden Professors", a collaboration of horticulture experts from Washington State University, Michigan State University, University of Minnesota  and Virginia Tech. They could easily subtitle their blog, "Everything You Know is Wrong". 

In a recent posting, Linda Chalker-Scott , Horticulture Professor at WSU, compiled extensive research findings on the relationship between excessive fertilizers and plant susceptibility to pests and disease.


Her conclusion: like too much candy given to children, too much fertilizer will sicken your garden plants.

Her more surprising solution: just feed your landscape trees and shrubs mulch

"For routine landscape needs," she reports, "use woody mulches rather than fertilizers and nitrogen-rich composts. This 'slow food' approach not only benefits your plants, but provides ideal habitat for mycorrhizal species, which have been shown to help restrict root uptake of excessive nutrients, while assisting with uptake of less available ones."

And another little gem hidden in that quote: mycorrhizae actually help plants avoid overeating (where are they when I need them?).

What about annuals, especially garden vegetables? Another of the "garden professors", Jeff Gillman of the University of Minnesota, cautions against using "balanced fertilizers".  The problem? When using a product like a 8-8-8 or 10-10-10 or 16-16-16, you may be adding excessive amounts of phosphorus and potassium to the soil, which is then susceptible to runoff, polluting our waterways. "I like a ratio of about 5-1-2 or 5-1-3 for an N-P-K ratio in a general use fertilizer," says Gillman.

The only improvement I would like to see to that blog would be to change the way to search for previous entries. The right sidebar lists the blogs by month, with no dropdown menu of titles. Even though their categories of "recent posts" and "by interest" is helpful, a more detailed list of titles would help gardeners find some of the best researched information for their garden problems.


  1. I have been using leaf mulch and happy frog soil conditioner only in my garden, and everybody makes delicious fruit!

  2. Hmm...Makes me wonder about the advice I received about throwing handfuls of fertilizer down at fruit and citrus trees once a month (that didn't come from you btw).

  3. LOVE the Garden professors ! They all have a way of breaking down their high-falutin' science-y research talk into gardener-speak.

  4. biochar, charcoal, will help balance feed also and hold water...roy