Greenwise Guide to Summer Weeds

Written by Greenwise Team
Published on June 23, 2021
Summer weeds, like most weeds, know a weakling when they see one. In the world of lawns and garden beds, weaklings are those bare spots or areas deprived of nutrition or simply a victim of poor irrigation. Weeds are extremely opportunistic and greedy, so they will take over those weak spots in a flash.  As the summer temperatures rise and our rainfall plummets, our lawns get stressed out, creating the perfect environment for weeds to take their cue and populate.

The Organic, Safe Approach to Getting Weeds Under Control

organic lawn
ORGANIC LAWNS ARE HEALTHY LAWNS THAT CAN OUTCOMPETE WEEDS! That’s where organic lawn care comes to the rescue. When you use a toxic herbicide, such as RoundUp, to get rid of your weeds, you aren’t making your turf stronger, you are simply masking the problem while creating an even bigger environmental issue. If you don’t know about the dangers of pesticides, you can learn more here. Organic lawn care works to solve the underlying problem of why you have weeds in the first place and keeps those weeds from recurring. Organic turf care takes an artisanal approach to your lawn, learning what it needs to thrive, which nutrients are missing, and adding the necessary ingredients to help strengthen your grass. It might be an organic fertilizer, seeding treatment, aeration or weed management, or a combination of those to help your lawn bounce back from its weedy self and be the lush, healthy lawn you hope for.

Greenwise Guide to Summer Weeds: Beware of These Weeds & Fungal Issues in Your Lawn


Nimblewill weed plant
HERE’S A CLOSE-UP LOOK AT NIMBLEWILL Nimblewill appears in mat-like patches that start small and grow larger. It’s often mistaken for Bermuda grass or bent grass but is shorter and has a fuzzy appearance. Its leaves are grayish green and course. Nimblewill grows in shady and sunny conditions but thrives in poorly drained soil. You can try to outcompete Nimblewill by increasing your mowing height (we recommend 3”), fertilization, and overseeding to enhance cool-season turf density, and improve the drainage in your lawn.


crabgrass weed
A CLOSE-UP LOOK AT CRABGRASS If you have crabgrass, it’s likely you have compacted soil, which is why you often find it in lawns and at the edges of sidewalks. To keep your soil from getting compacted, it’s important to aerate and fertilize. Crabgrass spreads in mats and smothers your desirable grass from growing. Cool season grasses fertilized in the fall and mid to late spring will go into mid-summer dormancy later and will compete better with the crabgrass. Overseeding in the fall helps create a thick turf in the spring, which shades the lawn and slows weeds from germinating. We always recommend you set your lawnmower at 3 inches high. Taller grass will shade the soil and decrease the germination rate of crabgrass seeds. Try to pull the crabgrass plants before they set seed. One plant can produce 150,000 seeds!


Nutsedge weed plant
NUTSEDGE ARE AGGRESSIVE WEEDS THAT ARE OFTEN CALLED NUT GRASS BECAUSE THEY RESEMBLE GRASS Nutsedges are aggressive and persistent weeds that commonly infest lawns, vegetable and flower gardens, and can be difficult to eradicate. Nutsedges are often called “nutgrass” because they closely resemble grasses. You can tell the difference by their stems, which are triangular or V-shaped in cross-section, while grass stems are hollow and round. Their leaves are thicker and stiffer than most grasses and are arranged in groups of three at the base. The bright yellow-green leaves of yellow nutsedge stand out clearly against turf, as do the dark green leaves of its purple relative. Left to grow tall, nutsedges produce distinctive spiky flower clusters: yellow-brown for yellow nutsedge and purple-brown for purple nutsedge. Nutsedges thrive in moist areas, and their presence often indicates that drainage is poor or you are watering too frequently. Instead of frequent shallow irrigation, irrigate deeply and infrequently. This supports deep, healthy grassroots and enhances resilience. Nutsedges thrive in compacted soil, so aerate your lawn as needed. Mow your lawn at the recommended height of 3”. Mowing too short can stress turf grasses and encourage nutsedge growth.

Summer Patch

summer patch lawn fungus
SUMMER PATCH SHOWS UP IN THE HEAT OF SUMMER AS ROUND CIRCLES OF DRY PATCHES According to the Purdue Extension, Summer patch symptoms begin to appear during the heat of summer. Initial symptoms resemble small (4-6 inches in diameter) circular or oval patches that are orange-brown and often occur in clusters. After it has been established, patches enlarge in a radial fashion. Most turf damage occurs at the leading edge of the patch. To relieve some of the summer stress, we recommend prolonged (deep) and infrequent irrigation. Aerating in the spring or fall promotes deep rooting, resulting in healthier turf that’s less prone to infection and more tolerant of summer stresses. Fertilization also helps fix any nitrogen deficiency.

Brown Patch

Brown patch lawn fungus
BROWN PATCH APPEARS AS IRREGULAR CIRCULAR SHAPES Brown patch disease is caused by a single species of fungus, Rhizoctonia. Like all of these weeds and fungal issues, we see it in mid- to late-summer when the weather is hot and humid. Brown patch is a foliar disease, meaning that it harms the blades of grass but not the crown of the plant or the root system, so that makes it easier for the grass to recover. Brown patch appears as irregular circular patches on the lawn that are brownish yellow in color and range from 6 inches to several feet in diameter. The affected leaves usually remain upright, and close inspection shows lesions on the leaves that are tan in color and irregular in shape with a dark brown border. The ring itself is typically 1/4 to 1/2 inch wide and is most visible in the morning. Sometimes grass within the ring is entirely killed, creating a sunken look to the patch, but more often the grass inside the patch simply becomes thinner than the surrounding lawn. Besides heat and humidity, the main factors inviting brown patches are excessive nitrogen and irrigation, which means that very lush and green lawns can be susceptible. Other factors include lack of air movement, poor soil drainage, excessive thatch, and compacted soils, which means that poorly maintained lawns can also be prone to brown patch disease. An organic fertilization program, combined with aeration, overseeding, and a proper irrigation technique all help to combat this disease from occurring on your lawn.