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Green Speak

Horticulture topics from gardens to lawns and then some.

The Dilemma with Weed-and-Feed Lawn Products


As a long winter's chill lingers into spring, the itch to get out in our yards has never seemed more compelling. One of the ritual tasks performed by many homeowners in the spring is applying weed-and-feed products to their lawn. Contained within these products is a pre-emergent herbicide to combat germinating weed seeds and then a helpful boost of nitrogen fertilizer to give our lawns that lush green appearance. Weed-and-feeds are a wonderful product of convenience by combining two tasks into one application- ideal for the weekend gardener, but not ideal for our lawns.

Pre-emergent herbicide's method of control is to inhibit the germination of seed or kill emerging seed. This means the homeowner must apply the chemical prior to the seed actually germinating. Let's use crabgrass as an example: We know that crabgrass germinates when soil temperatures rise above 55°F to 60°F for 7 to 10 consecutive days, so we must apply our pre-emergent when soil temperatures reach that window. Because crabgrass typically germinates by mid-April, crabgrass control is commonly applied by the first of April.

While crabgrass is germinating, our lawns are focusing much of their energy on root development to prepare for summer. As was mentioned prior, fertilizer gives that nice flush of green growth we so desire in our lawns. Nitrogen, the main nutrient in most lawn fertilizers, is the element that stimulates the green leafy growth in plants. By applying nitrogen and stimulating vegetative growth too early, the turf is left with an inadequate root system and a lawn that will be less resilient during a hot, dry summer.

The ideal lawn care timeframe is late summer into early fall to allow cool-season lawns to recover from a hot summer. This is when you should be fertilizing, overseeding, and core aerating. To combat crabgrass this spring, locate an herbicide product that does not contain any fertilizer. This may be tough to find in some of our big box stores, so you may need to try a few different locations, or ask a local garden center as they should carry these products. If a company treats your lawn, call them up and ask them to leave out the fertilizer when they are making their pre-emergent application this spring. Apply fertilizer later in the spring as temperatures warm up to the point where the lawn begins to put on vegetative growth, usually by mid-May.

To track soil temperatures in your area so you can time your crabgrass application perfectly, click HERE to view the Illinois State Water Survey's map of current soil temperatures. These are updated daily.

Click HERE to visit University of Illinois Extension's Lawn Talk webpage.


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