Crabgrass Preventors

April 10, 2015

Apply Crabgrass Preventors Now

Usually we start talking about crabgrass preventers now, but are telling people to wait several weeks before applying them. The warm weather and dry conditions -  until about a week ago - have warmed soils faster than normal this spring.

As of April 1, soil temperatures greater than 50F at a 4 inch depth were common across the state. Soil temperatures could be even higher depending on the soil type, moisture in the soil, sun exposure, and distance to a heat sink like a sidewalk, driveway, or street.

Crabgrass will germinate when soil temperatures are sustained between 55 and 60F. So preemergence herbicides for crabgrass should be applied soon. You should delay applying preemergence products on areas that winterkilled and will need to be reseeded or on any newly seeded areas. However, preemergence products such as Tupersan (siduron) or Tenacity (mesotrione) are safe on new seeding.

Avoid using preemergence products that are combined with fertilizer. Although most preemergence products available to homeowners contain nitrogen fertilizer, the spring flush of growth that occurs naturally in early April doesn't need encouragement from extra fertilizer. It is much easier to apply a standalone preemergence product now and a standalone fertilizer in early May than to have to mow twice a week during April.

Weed-n-feed preemergence products aren't always as convenient as they may seem. Standalone preemergence products can be found at most garden centers. If a combination preemergence and fertilizer product has to be used, then use the product with the lowest nitrogen content. This will be the product with the smallest first number of the three on a fertilizer bag, or the highest levels of a  slow release form of nitrogen. Another advantage of a standalone preemergence is that you can treat only problem areas and skip areas that don't have a history of crabgrass saving you money.

Since we've mentioned fertilization, let's quickly recap our recommendations for fertilizing cool season turf grasses such as bluegrass or fescue. I recommend and fertilize my own lawn with a small amount, maybe a half pound of actual nitrogen per 1,000 square feet or turf, at four times throughout the growing season. The best way to remember these is to fertilize by the holidays... Arbor Day or May Day (late April to early May), Memorial Day (late May), Labor Day (early September), and Halloween (late October).

The advantage of spreading out the fertilizer applications and waiting for the first application until around the first of May is this avoids the burst of growth that follows a heavy application of fertilizer. While rapid growth in the spring seems like the sign of a healthy lawn, it can actually set the lawn up for more problems in mid-summer.

Some homeowners are not willing to fertilize four times, they only want to fertilize twice... once in the spring and once in the fall. In this situation they will still want to make their first application around May 1 and wait until Halloween for the second application.

The reason this gets trickier is turf often needs a little fertilizer in early September to help recover if it has been a particularly stressful summer, but the late October application is still the most important in the fall. If we do have a particularly stressful summer on lawns, you may be able to get by with one application this spring, but still need to split the fall application, early September and late October.

For more information on lawn care, contact your local Nebraska Extension office.