Healthy Turf - Series 3 Article 2 - Creating a Healthy, Enduring Lawn

By Bobbie Herbs

Controlling Weeds

Spring is the optimal season to control weeds by using a pre-emergent herbicide as soil temperatures rise, and post-emergent herbicides once weeds have started actively growing. It’s important to remember what encourages weed growth - poor cultural methods. Improper mowing and fertilizing, shallow watering, and compacted soils cause a decline in turf health, and making room for weeds to take over. 

Generally, warm-season and cool-season grasses will benefit from spring weed prevention. Spreading a pre-emergent herbicide will prevent the weed seeds from germinating by forming a ‘shield’ over the soil surface. Pre-emergent herbicides impact germination of many weed seeds, including insidious crab grass. As the climate fluctuates, so does the soil temperature making it a little more difficult to predict when soil temperatures reach 50 degrees. It is better to check soil temperature monitoring websites.

Using Pre-emergent or Post-Emergent Herbicides

Most pre-emergent herbicides have a three-month lifespan, so any grass seeding will be inhibited during that period. It’s recommended to hold off over-seeding until fall, avoiding the dilemma of killing the weeds or filling brown spots. 

There are also post-emergence methods of removing weeds from your turf.  Dandelions can be controlled manually by snapping off their flower stems before they go to seed, or by digging them out by the roots, making sure to get the full tap root. Post-emergent herbicides are most effective when weeds are young and tender, and make require multiple treatments over a period of time to control broad leaf weeds. Be sure to use a selective, broad leaf herbicide when treating your lawn. 

Not all weeds are the same. Some are annuals and others perennials. This requires both pre-emergent and post-emergent tactics. 

Weed Types

There are several weed types in the Mid-Atlantic, including Broadleaf Winter Annuals, Broadleaf Summer Annuals, Broadleaf Perennials, and Grassy Winter Annuals.  You can read more about each type of weed here  https://extension.umd.edu/hgic/topics/lawn-weed-id-and-management

Annual weeds experience a full life-cycle in one year - germination, maturity, then go to seed.  Depending upon the weed, the life-cycle can begin at different times of the year. 

For instance:

Þ    Broadleaf Winter Annuals overwinter as mature plants prior to going to seed in spring followed by die off in summer.  When you identify these weeds in your grass – chickweed, dead nettle, and bittercress – use a post-emergent herbicide to battle them.

Þ    Broadleaf Summer Annual seeds germinate in spring as the soil warms and die in fall with the first frost. Carpetweed, knotweed, and spurge are examples treat with a post-emergent herbicide applied when the weed is actively growing.

Þ    Perennial weeds persist from year to year, reproducing by both vegetative growth (rhizome, stolon, corm, etc.) and seed.  Applications of herbicide in spring and fall may be required. A broadleaf post-emergent is recommended for spring during active growth.  Ground ivy, wild onion, plantain, buttercup, and dandelion are part of this group.

Þ    The fourth group are grassy weeds. Perennials, these include weeds that germinate in late summer. Many have behaviors like the turf you are trying to grow and can be difficult to manage. A pre-emergent can be used in fall to control nut sedge, quack grass and others in this category.

Feeding your Lawn

Now that you have gotten ahead of the weeds, it’s time to prepare for the feeding of your lawn. Keep in mind that fertilizers for grass will also feed broad leaf weeds so timing is important. Think 90 days from your pre-emergent application.

Once again be gentle, as weather is unpredictable, the ground can be soggy and new grass growth is tender. 

Let’s look at the variations of care based on the type of grass you have. 

Þ    Cool-season grasses (fescue, bluegrass, and rye) have two growth spurts. The spring spurt offers tender leaves that can easily burn is late spring and summer heat. Fertilize lightly if your lawn is in bad shape, and save heavier fertilization for fall during their last growth spurt. Or just focus on fertilizing in fall.

Þ    Warm-season grasses (Zoysia, St. Augustine, Centipede, and Bermuda) benefit from fertilizer in late spring as soon as the lawn “greens up”.  If you have applied a pre-emergent be aware of the temptation to fertilize during its active growth period.  Otherwise fertilize after the last frost.  

Soil Tests and Lime Application

Your soil test may indicate that your lawn could benefit from a lime application. Lime’s primary purpose is bringing acidic soils to a more neutral state. Remember in high school your lessons in pH, not necessarily the details of logarithmic scale but the measurement of bases and acids from 0-14. High pH is considered alkaline or basic, (like bleach which has a pH of 13.5). Whereas low pH is acidic, (like lemon juice or vinegar which have a pH of 2). Most turf grass enjoys a more neutral soil, with a pH 6 to pH 7. 

High acidity is common in Burlington County, the heart of the Pinelands. Acid soils limit the availability of nutrients your lawn requires, therefore maintaining a neutral pH is essential to healthy turf. Recognize pH is always changing, especially in climates with lots of rainfall washing away Calcium resulting in lowered pH levels. When you apply lime, follow the directions carefully and take precautions around acid-loving plants like azaleas, rhododendrons and hydrangeas. Be sure to wait three weeks after fertilizing, ensuring no adverse effects to your lawn. 

Next week we will talk about Integrated Pest Management.