Fertilizing lawns

Judith Adam

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My lawn has more “constituents” (that is, weeds and wild plants) than grass, but it started out with the typical cool-season grasses: perennial ryegrass, Kentucky bluegrass and fescue. Occasional applications of fertilizer keep the cultivated grasses competitive with the other constituents, and my sin of omission has been not providing enough supplemental lawn food.

I have two bags of lawn fertilizer waiting in the garage, but I’m holding off on using them for a while longer. Understanding how grass plants grow is helpful in devising a fertilizer strategy. Cool-season grasses lose much of their root systems over winter, and must grow new roots in spring. If they can establish long new roots (before diverting energy to blade production), they’ll be able to reach groundwater in midsummer droughts more easily.

Temperature is a good guideline for timing fertilizer application. Grass roots grow best in daytime temperatures between 12° and 18°C, similar to the temperatures we’re just beginning to have this spring in southern Ontario. Blades grow best between 19° and 24°C. Applying fertilizer too early forces blade growth and shortens roots. When drought hits, grass plants are compromised and some die, thinning the lawn. I’m waiting until mid May, when day temperatures have warmed, before feeding the lawn. That gives me another month of trying to eliminate weeds before they enjoy a tasty fertilizer meal along with the grass. I’ll fertilize again in autumn, hoping the two feedings, combined with overseeding, will help get my lawn back on its feet.


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