May is grub prevention month. One application of GrubEx now stops the kind of root damage that leaves entire sections of your lawn peeling up like carpet in August. This is also your last realistic window for spring broadleaf weed control before summer heat makes herbicide applications risky.

What Should Cool-Season Lawns Do in May?

Cool-season grasses in Zones 2-7 are in peak spring growth during May. Kentucky bluegrass is spreading through rhizomes, tall fescue is thickening up, and the lawn should be looking its best. Your job this month is to maintain momentum and prevent problems before they start.

Second Spring Fertilizer Application

If you applied your first round in April, May is the time for a second light feeding. Keep the rate moderate at 0.5 to 0.75 lb of nitrogen per 1,000 square feet. This isn’t the time for heavy nitrogen. That’s what September and October are for.

A slow-release product stretches the feeding window and avoids the surge-and-crash growth pattern that quick-release fertilizers cause. Last spring, a homeowner in Ohio showed me his lawn after three consecutive years of heavy spring feeding. Looked incredible in May, turned into a brown patch disaster every July. Root systems were almost nonexistent below two inches.

Mow Weekly at 3-3.5 Inches

The one-third rule still governs everything. If you’re maintaining at 3.5 inches, mow when the grass reaches about 5 inches. Kentucky bluegrass and perennial ryegrass may need mowing every five to six days in May as growth rates peak.

Leave the clippings on the lawn. Grass clippings decompose quickly and return roughly 25% of the nitrogen you applied back to the soil. According to the University of Minnesota Extension, returning clippings reduces annual fertilizer needs by up to one full application.

Mowing Task	Details
Height (KBG, Ryegrass)	3 - 3.5 inches
Height (Tall Fescue)	3.5 - 4 inches
Frequency	Every 5-7 days
Blade condition	Sharpen every 8-10 hours of mowing
Clippings	Leave on lawn (grasscycling)

Apply Grub Prevention Now

This is the big one. Preventive grub control with chlorantraniliprole (the active ingredient in Scotts GrubEx) needs to go down in May or June, before Japanese beetle and June bug larvae hatch and start feeding on roots.

Chlorantraniliprole works by being present in the soil when eggs hatch in late June through July. It takes time to move into the root zone, which is why applying in May gives the best results. Water it in with 0.5 inches of irrigation within 24 hours of application.

Skipping grub prevention is a gamble that costs far more to fix after the fact. We’ll cover this in detail below.

Spot-Treat Broadleaf Weeds

May is your last comfortable window for broadleaf herbicide applications on cool-season lawns. Once daytime temps consistently hit 85 degrees F, most selective herbicides risk damaging your turf.

Target dandelions, clover, and plantain with a product containing 2,4-D and dicamba. Spray when weeds are actively growing and temps are between 60 and 80 degrees F. A pump sprayer with a fan-tip nozzle gives better coverage than a hose-end sprayer for targeted applications.

Our spring lawn care checklist covers the full weed control timeline from March through May.

Watch for Early Signs of Fungal Disease

Dollar spot, brown patch, and red thread all begin appearing in late May when humidity rises and nighttime temperatures stay above 60 degrees F. Early symptoms include circular brown patches 2-6 inches in diameter (dollar spot) or irregular larger patches with a dark border (brown patch).

The best defense is cultural: water in the morning, don’t over-fertilize with nitrogen, and maintain proper mowing height. Fungicides are a last resort, not a routine application.

What Should Warm-Season Lawns Do in May?

Warm-season grasses in Zones 7-10 are hitting full stride in May. Bermuda is in aggressive growth mode, St. Augustine is filling in, and zoysia is thickening up. This is the month to push growth and stay ahead of pests.

Fertilize for Full Growth Mode

Bermuda grass in full growth mode needs regular feeding. Apply 0.75 to 1 lb of nitrogen per 1,000 square feet in May. Bermuda is a heavy feeder during its active growing season and responds well to monthly applications through August.

St. Augustine gets a lighter touch: 0.5 to 0.75 lb N per 1,000 square feet. Over-fertilizing St. Augustine promotes rapid stolon growth that increases thatch buildup. For zone-specific recommendations on bermuda feeding schedules, see our bermuda grass care guide.

Warm-Season Grass	May N Rate (lbs/1,000 sqft)	Frequency
Bermuda	0.75 - 1.0	Monthly through August
Zoysia	0.5 - 0.75	Every 6-8 weeks
St. Augustine	0.5 - 0.75	Every 6-8 weeks
Centipede	0.25 - 0.5	Once in May, once in July max

Centipede grass needs the least nitrogen of any warm-season turf. The University of Georgia Extension recommends no more than 1-2 lbs of nitrogen per 1,000 square feet for the entire year. Exceeding that rate causes centipede decline, a condition where the grass thins out from too much fertilizer.

Deep Water 1-1.25 Inches Per Week

Warm-season grasses need deep, infrequent watering to develop strong root systems. Split your weekly inch into two sessions of 0.5 inches each, spaced three to four days apart.

Bermuda grass roots can reach 6 feet deep in sandy soils with proper deep watering. Shallow daily sprinkles keep roots in the top 2 inches, making the lawn vulnerable to drought stress the moment you skip a day. Use our watering calculator to figure out the right runtime for your sprinkler system.

Monitor for Chinch Bugs and Armyworms

St. Augustine lawns should be on high alert for chinch bugs starting in May. These tiny insects feed by sucking plant juices from grass blades, causing irregular yellow patches that turn brown. The damage often mimics drought stress.

Test for chinch bugs by pressing both ends out of a coffee can, pushing it 2 inches into the soil at the edge of a damaged area, and filling it with water. Chinch bugs float to the surface within five minutes if present.

Armyworms hit bermuda and zoysia lawns, especially in the Southeast. They feed at night and can strip a lawn bare in 48 hours. Look for birds congregating on your lawn. Flocks of starlings or grackles feeding in your turf is a reliable sign of armyworm activity underneath.

Mow Frequently

Bermuda grass may need mowing twice per week in May. This isn’t optional for a clean-looking bermuda lawn. Letting bermuda grow tall and then scalping it back stresses the plant and creates brown, stemmy patches.

Zoysia and St. Augustine hold at once per week unless growth is unusually rapid. St. Augustine stays at 3-4 inches, which means mowing when it reaches about 5 inches.

Apply Post-Emergent Herbicides for Breakthrough Weeds

Any weeds that made it past your pre-emergent barrier need targeted treatment now. For bermuda lawns, products containing atrazine handle most broadleaf and some grassy weeds. St. Augustine tolerates atrazine at labeled rates.

Do not use atrazine on zoysia or centipede without checking the product label for specific cultivar tolerance. Some zoysia cultivars are sensitive. When in doubt, hand-pull or use a targeted broadleaf-only herbicide.

Why Is Scotts GrubEx the Product of the Month?

Scotts GrubEx contains chlorantraniliprole, a preventive grub control that stops grub damage before it starts. This is the single most important preventive application of the year for lawns in Zones 4-8 where Japanese beetles, June bugs, and European chafers are common.

Key facts about GrubEx:

• Preventive, not curative. It must be in the soil before grub eggs hatch. Applying after you see damage is too late for this product.
• One application protects all season. A single May or June application provides season-long control through fall.
• Apply and water in. Spread with a broadcast spreader and irrigate with 0.5 inches of water within 24 hours. The water moves the active ingredient into the root zone where grubs feed.
• Low toxicity to pollinators when used as directed. Chlorantraniliprole has a favorable environmental profile compared to older grub control chemicals like trichlorfon.

Check GrubEx price on Amazon

For even application, a broadcast spreader is essential. Our fertilizer spreader reviews cover the best options from Scotts, Earthway, and Echo.

What Happens If You Skip Grub Prevention?

You won’t see the damage until August. By then, grubs have been feeding on grass roots for six weeks, and entire sections of turf pull up like loose carpet.

The Timeline of Grub Damage

Here’s what happens underground when you skip prevention:

Month	What’s Happening Below Ground
May-June	Adult beetles lay eggs in turf
July	Eggs hatch, tiny grubs begin feeding on roots
August	Grubs are half-grown, damage becomes visible
September	Full-sized grubs cause severe thinning and dieback
October	Grubs move deeper into soil for winter

By August, you’re stuck with curative treatments like trichlorfon (Dylox), which cost more per application and are less effective than prevention. Trichlorfon also has a narrower safety margin and requires precise timing to work.

A preventive GrubEx application costs roughly $25-35 for 5,000 square feet. Repairing grub-damaged turf (overseeding, topdressing, possibly sodding dead areas) runs $200-500 or more depending on the extent of damage.

One renovation project I worked on in central Indiana started because the homeowner skipped grub prevention for two years straight. The entire backyard, about 4,000 square feet, needed to be stripped and re-sodded. That was a $2,800 job that a $30 bag of GrubEx would have prevented.

May 2026 Quick-Reference Checklist

Cool-Season (Zones 2-7):

• Second spring fertilizer (0.5-0.75 lb N/1,000 sqft)
• Mow weekly at 3-3.5 inches
• Apply GrubEx, water in within 24 hours
• Spot-treat broadleaf weeds (last spring window)
• Monitor for dollar spot and brown patch symptoms
• Maintain 1 inch/week irrigation

Warm-Season (Zones 7-10):

• Fertilize bermuda (0.75-1 lb N), lighter rates for other types
• Deep water 1-1.25 inches per week
• Check St. Augustine for chinch bugs weekly
• Watch for armyworm activity (bird feeding on lawn)
• Mow bermuda twice per week if needed
• Apply post-emergent herbicides for breakthrough weeds

Frequently Asked Questions About May Lawn Care

When exactly should I apply GrubEx in May?

Any time in May works. The active ingredient, chlorantraniliprole, has a long residual in soil. Applying in early May gives it more time to distribute through the root zone before eggs hatch in late June. Water it in within 24 hours of application.

Can I fertilize and apply GrubEx on the same day?

Yes. Apply fertilizer first with your spreader, then make a second pass with GrubEx. Water both in with 0.5 inches of irrigation. Combination products exist, but separate applications give you more control over rates.

How do I know if I have grubs?

Cut a 1-foot-square section of turf 3 inches deep and peel it back. Count the grubs. Fewer than 5 per square foot is normal. More than 10 per square foot causes visible damage. This test works best in August and September when grubs are actively feeding.

Is it too late to apply pre-emergent in May?

For crabgrass prevention in Zones 6-7, yes. Soil temps have passed the germination threshold by May. In Zones 3-5, early May might still work if spring was cold. Check soil temps at 4 inches. Above 55 degrees F for several consecutive days means crabgrass has already started germinating.

Should I bag or mulch clippings in May?

Mulch them. Grass clippings do not cause thatch buildup. That’s a persistent myth. Clippings are 80-85% water and decompose within days. They return nitrogen, potassium, and phosphorus to the soil. The only exception is if the lawn is severely overgrown and clumps of clippings are smothering the grass underneath.

How often should I water bermuda grass in May?

Two to three times per week, delivering a total of 1 to 1.25 inches. Bermuda prefers deep, infrequent watering over daily light sprinkles. Sandy soils may need three sessions per week. Clay soils hold moisture longer and usually need just two.

What’s Coming in June?

June brings summer heat stress management for cool-season lawns and peak growth demands for warm-season turf. Raise your cool-season mowing height, maintain your irrigation schedule, and start watching for fungal pressure as humidity climbs. Our spring lawn care guide covers the transition into summer in detail.

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