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When to Fertilize the Lawn

If you go into a store like Home Depot on the first beautiful weekend in spring you will see the fertilizer bags flying off the shelves.  Companies like Scott’s will be running their advertising blitz and everyone is looking forward to spring and the green grass and blue skies.

Last year  in Ontario we had the warmest mid-March on record, and I saw many people out fertilizing their lawns...which, for me at least, brings up the issue of timing.  When is a good time to be fertilizing your lawn?

To begin with, let’s establish that the purpose of fertilizer is to help your grass grow up healthy and sturdy.  Following this, it would stand to reason that you should fertilize when your grass is growing.  Cool season grasses such as we have in Ontario are a bit different from warm season grasses - they have two rather distinct growing seasons in the Spring and the Fall, broken up by a dormant season during the blazing heat of July/August.  So we should be fertilizing in Spring and in Fall to assist the grass during it’s growth period as opposed to trying to coax it to grow during it’s dormant period.  If we fertilize when the grass is not physiologically ready to use the nutrients we will be wasting fertilizer and, perhaps worse, promoting growth of those elements who may be in a growth period at the time - weeds.

So, despite the temptation of a clear, sunny Saturday in early March, it would be advisable to wait a little longer before applying fertilizer unless the grass has fully ‘greened up’.  Any earlier and your lawn has likely not fully come out of it’s dormant season.

The second most important application after the spring is the late fall application.  Fertilizing in late fall helps the plants ‘weather’ the winter stresses, allowing them to rebound strong in spring with healthy growth.

A suggested fertilization schedule might be, depending upon the weather that season of course:

May 1st - if the lawn is greening up well
July 1st - or a little earlier -  grass will still be in a growth phase
September 1st - grass will be entering it’s second growth phase of the season
Mid-late October - the ‘winterizer’ application - should be done after grass is stopped growing but still green - a few weeks from ground freezing