University of Minnesota Extension

Home > Extension in your Community > Lawn Fertilizer and Herbicide Best Practices

print icon email icon share icon

Lawn Fertilizer and Herbicide Best Practices

source: istock

University of Minnesota Extension, Stearns County News
April 29, 2014        
Source:  Beth Berlin, Extension Educator-Horticulture
University of Minnesota Extension
Stearns & Benton Counties


Lawn Fertilizer and Herbicide Best Practices
By Beth Berlin, University of Minnesota Extension

ST. CLOUD, Minn. (4/30/14) — This spring has certainly brought its abundance of rain, and we are back at conditions where lawn care should be put aside until the ground has firmed up and dried out again.  Traditional spring lawn care has typically included fertilizing and putting down herbicides for the weeds.  Knowing the correct time and rate of application is critical, and some of it may surprise you.

Fertilizing lawns in the spring has been an ongoing practice for years; however the best time to fertilize your lawn is late summer and fall.  The benefits to fall fertilizing verses spring application include: 1) Quicker, earlier green-up in the spring without additional shoot growth 2) Reduced occurrences of summer disease 3) Increase in carbohydrate reserves 4) Additional period of green in the fall.  All of which are reason enough to apply fertilizers in the fall rather than spring, but it may take a bit more convincing to get you to change your habits.  Another primary reason to do fall fertilizing rather than a spring application is because although fertilizing in the spring gives the grass plants a surge of nitrogen to burst a beautiful green, it reduces the plant’s energy reserves. Unfortunately this will result in a weaker plant during the stresses of the summer heat and dry periods because rather than putting down deeper roots in the spring the plant focused on having greener tops and may ultimately reduce its chances of survival.

The question now is what if you didn’t do a fall fertilizing program? One option is to skip a spring fertilizer application and simply wait till late summer or early fall.  You would sacrifice some aesthetics but it would help get you on the right track to the optimal application time.  Another option would be to apply fertilizer this spring and then get in the routine of doing a fall application.  If you opt to go this route, it is important to wait until the grass has reached mowing height before applying only a light application.  This way the plant focuses on putting energy into root growth rather than shoot growth.  Applying fertilizer too early in the spring will actually be ineffective for both your grass plants and your wallet.  If applied too early, nutrients especially nitrogen will actually leach to a depth where it is inaccessible to the plant’s roots.  If you question whether your lawn needs fertilizer, a simple solution is to have a soil test performed.  Information about having a soil test done can be found at your local University of Minnesota Extension Office or online at

Another common question in the spring is when to apply pre-emergent herbicide for the crabgrass and other spring germinating weeds?  Timing is critical, and truly watching the forecast diligently is important.  The optimal time to apply pre-emergent herbicides is about two weeks before the crabgrass germinates for the year, which will occur when soil temperatures reach about 55 degrees Fahrenheit.  Soil temperatures can be checked with a soil thermometer or even a kitchen meat thermometer.  Typically these soil temperatures are reached around mid to late May, so pre-emergent would be applied between early to mid-May; however each year varies. Each yard and even separate areas within your yard might obtain these conditions at different times, especially along sidewalks or driveways.  Applying herbicide across the entire yard may not be necessary, instead target areas where crabgrass has been an issue in the past.  Overall this will result in the use of less chemicals and cost savings.

Post-emergent herbicides may be applied anytime when the weeds are actively growing as well as when environmental conditions are correct.  Post-emergent herbicides have optimal results in 60-80 degree Fahrenheit, no winds, and a clear forecast with no precipitation for 48 hours. Ideal application of post-emergent herbicides on broadleaf weeds is applied in spring from May 1st to June 1st.  *With all herbicide applications, be sure to read the label thoroughly and follow all application rate and safety directions. 

Because the market is full of products that contain both pre-emergent herbicides and fertilizer, it is important to know the contents and understand your lawn will be healthier by buying separate products to apply at the appropriate time.  Do you wallet and your lawn a favor by changing your old habits and putting fertilizer down in the fall and using herbicides at the right time in the spring. Timing is everything!

* Pesticide products should always be used in accordance with all label directions. Pesticide label directions can and do change over time. Therefore, when a pesticide product is purchased, it is the responsibility of the user to read and follow the label directions attached to the product container. The plant or site of the intended application must be listed on the label. Any use inconsistent with the label is a violation of Federal law.