When to weed and feed depends on which weed and feed is in your garage, and most guides skip that question entirely. The bags look alike, but some carry a pre-emergent that has to go down before crabgrass seeds sprout in early spring, and others carry a broadleaf killer that works best on dandelions and clover in the fall. Put either one down at the wrong time and you’ve paid for a fertilizer application with a herbicide that did nothing.
There’s a second catch. University extension services from Illinois to Florida point out that the “weed” half and the “feed” half rarely want the same calendar date. This guide sorts out both problems and gives you dates, temperatures, and the conditions on application day that decide whether it works.
Quick Answer: Check the label first. A pre-emergent (crabgrass) weed and feed goes down in early spring, a week or two before soil reaches 55°F, which is about early April in central Illinois and mid-February to early March in south Georgia. A broadleaf (post-emergent) weed and feed works best on cool-season lawns in fall, mid-September to early November (Iowa State Extension), with late spring as the backup. On warm-season lawns, wait until the grass has fully greened up. Apply granules to wet foliage, skip mowing 2 to 3 days before and 3 to 4 days after, and hold off on rain or watering for 24 hours.
First, Check Which Weed and Feed You Bought: Pre-Emergent vs. Post-Emergent
Read the active ingredients on the back of the bag. That tells you which calendar you’re on.
| Type | What it does | Common actives | When it works |
|---|---|---|---|
| Pre-emergent weed and feed | Stops crabgrass and other seeds from establishing | Prodiamine, dithiopyr, pendimethalin | Before seeds germinate, early spring |
| Post-emergent (broadleaf) weed and feed | Kills weeds already growing through the leaves | 2,4-D, MCPP (mecoprop), dicamba | When weeds are actively growing; fall is best for perennials |
| Southern weed and feed with atrazine | Pre- and post-emergent activity on annual broadleaf weeds | Atrazine | On centipedegrass and St. Augustinegrass after green-up |
| Combination products | Both pre- and post-emergent | Varies | Timing is a compromise for both |
Most broadleaf weed and feeds won’t touch crabgrass, because crabgrass is a grass. If crabgrass is your main problem, you need a pre-emergent, and our guide on when to apply crabgrass preventer covers that timing in detail.
When to Weed and Feed by Grass Type: Spring and Fall Windows
| Lawn type | Pre-emergent weed and feed | Broadleaf weed and feed |
|---|---|---|
| Cool-season (Kentucky bluegrass, tall fescue, ryegrass) | Early spring, before soil hits 55°F | Best: mid-September to early November. Backup: late spring |
| Warm-season (bermudagrass, zoysia, St. Augustinegrass, centipedegrass) | Late winter, before soil hits 55°F, often before the grass greens up | After full green-up in late spring, or early fall before dormancy |
Cool-Season Lawns
For a pre-emergent product, the target is the week or two before crabgrass germinates. Chris Enroth, a University of Illinois Extension horticulture educator, explains that crabgrass sprouts once soil holds 55 to 60°F for 7 to 10 days, so central Illinois homeowners apply in early April ahead of mid-April germination.
For broadleaf weeds, fall wins. More on that below.
Warm-Season Lawns
Warm-season grass is the tricky one. The University of Georgia Extension gives south Georgia a pre-emergent window of February 15 to March 5, before soil reaches 55°F. But it also warns that nitrogen weed and feeds should wait until 4-inch soil temperature holds at 65°F, and that post-emergent herbicides shouldn’t go down during green-up, when the turf is most easily injured. For centipedegrass, UGA notes that by the time the lawn is fully green and ready for fertilizer, it’s usually too late for a pre-emergent.
In practice: on a warm-season lawn, use a pre-emergent without nitrogen in late winter, or a potassium-only combination product, and save the broadleaf weed and feed for after green-up.
When to Weed and Feed in Spring vs. Fall: Why Fall Wins for Broadleaf Weeds
Spring is when dandelions bloom, so it’s when people reach for the bag. It’s also when broadleaf herbicides work worst on perennial weeds.
Iowa State University Extension explains why: in fall, perennial broadleaf weeds move carbohydrates from their leaves down to their roots for winter, and the herbicide rides along. Spring applications are less effective. Purdue’s turfgrass team says October and November treatments kill the whole weed instead of “burning off the top,” and winter finishes off many of the weakened ones.
Illinois Extension adds a safety angle: spring and early summer applications carry a higher chance of injuring trees and other landscape plants, since their new growth is tender.
So for dandelion, clover, and plantain on a cool-season lawn, treat in fall. If you must treat in spring, do it once the weeds are actively growing and before temperatures climb.
The Timing Conflict Inside Every Bag
Even with the right herbicide window, the fertilizer part usually wants a different date.
- Cool-season lawns: Enroth notes that nitrogen pushed in early spring, when crabgrass preventers go down, drives leaf growth at the expense of roots, leaving the lawn less ready for summer. The better spring feeding is around mid-May in central Illinois, and the best feeding of the year for cool-season grass is late summer into early fall. His advice is to buy a crabgrass preventer without fertilizer in spring.
- Warm-season lawns: UGA and UF/IFAS both say pre-emergents belong much earlier in the year than fertilizer. UF/IFAS goes further and does not recommend weed and feed at all for Florida-Friendly landscapes, because one or both halves usually end up mistimed.
The fall broadleaf weed and feed on a cool-season lawn is the one combination where timing lines up: fall is a good time to kill perennial weeds and a good time to feed the grass. Our guide on when to fertilize your lawn in fall covers the feeding side.
What Is the Best Month to Put Down Weed and Feed?
| Region and product | Best month |
|---|---|
| Central Midwest, pre-emergent (crabgrass) | Early April |
| Cool-season, broadleaf weed and feed | Mid-September through October |
| South Georgia, pre-emergent | Mid-February to early March |
| Warm-season, broadleaf weed and feed | Late spring after full green-up, or September |
Midwest and Georgia dates from University of Illinois and UGA Extension; cool-season fall window from Iowa State. Farther north, pre-emergent dates shift later; track soil temperature rather than the calendar.
What Months Can You Use Weed and Feed?
Roughly February through June and September through early November, depending on product and region. Avoid midsummer heat and dormant winter months. A soil thermometer is a better guide than a calendar: pre-emergents go down before soil hits 55°F, and nitrogen on warm-season grass waits until 65°F at 4 inches.
Temperature, Weather, and Dew: The Application-Day Checklist
The day you spread matters as much as the month.
- Temperature: Purdue recommends sunny days above 55°F for fall broadleaf work. Illinois says to avoid days over 85°F, since these herbicides can vaporize and drift for days afterward. UGA says turf tolerance drops above 90°F, and UF/IFAS warns that pre-emergents can injure lawns when temperatures stay above 90°F for three days running.
- Wet leaves: Iowa State says granular weed and feed must stick to the weed, so apply in the early morning while dew is on the grass, or water lightly first.
- No rain: Iowa State says to apply when no rain is forecast for 24 hours.
- Soil moisture: Illinois says weeds need adequate soil moisture to be actively growing. Treating drought-stressed weeds wastes product.
Do You Weed and Feed Before or After Mowing?
Mow first, then wait. Iowa State says not to mow for two to three days before a broadleaf treatment, so there’s enough leaf for granules to land on, and to wait three to four days afterward so the weeds absorb and move the herbicide to their roots. Our guide on whether to mow before fertilizing covers plain fertilizer, which follows different rules.
Should I Water After Weed and Feed?
For a broadleaf weed and feed, no, not for 24 hours. Iowa State says don’t irrigate treated lawns within that window, or you’ll wash the herbicide off the leaves. Pre-emergent products are different: many labels ask you to water them in so the herbicide reaches the soil. Read your bag. Our guide on how long after weed and feed you can water breaks this down by product type.
How to Apply Weed and Feed
- Confirm the product matches your grass. Some weed and feeds safe on bermudagrass will damage St. Augustinegrass. The label lists approved grasses.
- Mow two to three days ahead.
- Calibrate the spreader to the setting on the bag. Purdue’s guidance is that more isn’t better.
- Apply in the morning on dewy grass, or after a light watering.
- Spread evenly and keep granules out of flower beds, vegetable gardens, and off driveways.
- Skip watering and mowing for the times above.
- Leave clippings on the lawn for the next few mowings rather than using them as mulch in garden beds, as manufacturers advise.
When Not to Apply Weed and Feed
- During green-up on warm-season grass. UGA says injury risk is highest during the transition from dormancy to growth.
- In heat over 85 to 90°F or during drought. Turf tolerance drops, weeds are harder to kill, and herbicides can vaporize.
- On dormant lawns or frozen ground. Neither the weeds nor the grass are taking anything up.
- Before a rainstorm, or right before a scheduled irrigation cycle.
- Over tree root zones with dicamba products, unless the label allows it (see below).
- On new seeding (see below).
Around Trees and Shrubs
This is the warning most guides leave out. UF/IFAS notes that tree and shrub roots extend well beyond the drip line, mingle with turf roots, and absorb herbicide from weed and feed. Illinois Extension points to dicamba specifically and says to check the label for hazards over tree root zones, adding that a healthy shade tree is worth more than a weed-free lawn. If your lawn is under mature trees, spot-treat instead of broadcasting.
On New Seeding or Before Overseeding
Illinois Extension says to wait four mowings before treating a newly seeded lawn, and to wait 30 days after a broadleaf treatment before seeding. A pre-emergent weed and feed is worse: it blocks grass seed the same way it blocks weed seed, so skip it entirely in a fall you plan to overseed.
Spot-Treat Instead? When Weed and Feed Is the Wrong Tool
Weed and feed treats every square foot of lawn. If your weeds are scattered patches, that’s a lot of herbicide for a small problem. Illinois Extension recommends spot-treating when only a few areas have weeds, and Purdue notes that liquid sprays are generally more effective than granular weed and feed when applied correctly.
A simple rule: if weeds cover most of the lawn, a fall broadleaf weed and feed makes sense. If they’re scattered, use a spot spray and feed separately on the right schedule. Our when to fertilize lawn guide has that calendar.
If most of your weeds are in beds, borders, and along fences rather than in the grass, a herbicide on the lawn won’t reach them. LawnGuru’s weeding service averages $151, with most jobs between $134 and $325, for hand-pulling and clearing beds.
Frequently Asked Questions
How often can you apply weed and feed?
Follow the label’s annual limit, which for most products is a small number of applications per year. A sensible pattern on a cool-season lawn is a pre-emergent without fertilizer in spring and one broadleaf weed and feed in fall.
Does weed and feed kill crabgrass?
Most broadleaf weed and feeds don’t. Crabgrass is a grass, so you need a pre-emergent applied before it germinates, or a post-emergent labeled specifically for crabgrass.
Can I weed and feed in the fall?
Yes, and for broadleaf weeds on cool-season lawns, it’s the best time. Iowa State recommends mid-September to early November. On warm-season lawns, apply in early fall while the grass is still actively growing, before it heads into dormancy.
Does weed and feed work?
It works when the herbicide matches the weed and the timing matches the product. It tends to fail when a pre-emergent goes down after weeds have sprouted, when a broadleaf product goes on dry leaves, or when rain washes granules off within a day.
Can I put down grass seed after weed and feed?
Wait 30 days after a broadleaf weed and feed, per Illinois Extension. After a pre-emergent product, wait the full period on the label, which is often several months.
Is weed and feed safe for St. Augustine grass?
Only products labeled for St. Augustinegrass. UGA notes atrazine-based weed and feeds can be used on St. Augustinegrass and centipedegrass after green-up. Products made for northern lawns may injure it, and UF/IFAS advises against weed and feed in Florida altogether.
Is 20 minutes enough time to water grass?
It depends on your sprinkler’s output, not the clock. Set a few straight-sided cans on the lawn, run the zone for 20 minutes, and measure the depth. After weed and feed, the bigger question is timing: wait 24 hours before watering a broadleaf product, or water in a pre-emergent if the label says to.
