When should I apply a fall pre-emergent in Los Angeles, CA?

In a typical year a fall pre-emergent in Los Angeles, CA goes down before October 28 — the median date the city's shallow soil cools to and stays at or below ~70°F on a 7-day average, which is when winter annuals start germinating. The barrier has to be down and watered in ahead of that, not on it. Because the date has ranged October 12 – November 17 across the record, read a soil thermometer rather than applying on the same weekend each year.

Is it too late for a fall pre-emergent in Los Angeles, CA?

Whether a fall pre-emergent is too late in Los Angeles, CA turns on germination, not a date on a calendar. Once soil there is past ~65°F — typically around November 14 — this season's winter annuals are coming up, and a pre-emergent cannot touch a plant that has already emerged. Germination runs for weeks rather than finishing in a day, so an application just past that line still catches the stragglers; well past it, the honest answer is a post-emergent option now and an earlier start next year.

Does one application cover the whole season in Los Angeles, CA?

Whether one fall pre-emergent application covers the whole season depends on the product, not on Los Angeles, CA — though locally, germination runs from the October 28 crossing to roughly December 27 – January 26 on University of Tennessee Extension's two-to-three-month figure. The section above sets out which pattern extension publishes for which grass, and the constraint underneath both: a split divides one year's labeled allowance rather than adding to it. Your label decides.

Does my USDA zone tell me when to apply in Los Angeles, CA?

A USDA hardiness zone does not set fall pre-emergent timing in Los Angeles, CA, and this page's dataset shows that rather than asserting it. Los Angeles, CA is zone 10, and the 3 zone-10 metros in this dataset spread 66 days apart on their own crossings — from San Francisco, CA on August 24 to San Diego, CA on October 29. A hardiness zone measures average winter cold, not how fast shallow soil gives up its summer heat in autumn, so latitude, elevation and how maritime the climate is all move the crossing inside one zone band — which is why this page is built on Los Angeles, CA's own soil records. What the zone does place is the catalog: which grasses are rated viable at zone 10, and so which of the two published patterns this page leads with. Which one applies to your lawn is settled by what is growing in it, not by the band and not by this page.

Does Poa annua matter in a dormant lawn in Los Angeles, CA?

A dormant lawn is where Poa annua shows worst. A warm-season lawn going straw-brown for the winter turns every patch of bright green annual bluegrass into a feature, and the same plants then compete with green-up in spring before dying out in the heat. Clemson groups it with chickweed, henbit and purple deadnettle as winter annuals that "germinate in the fall, grow through the winter, set seed, and die as temperatures rise in early summer" — which is why the fall barrier is the point of intervention rather than a spring rescue.

How far apart are Los Angeles, CA's two published dates?

Los Angeles, CA's two published fall dates are 17 days apart: soil crosses ~70°F around October 28 and reaches ~65°F around November 14. Both are medians over the years each threshold was actually crossed, so that is the gap between two medians and not a measurement of a typical autumn. Aim to be finished before the front of it rather than inside it — a pre-emergent needs rain or irrigation to move it into the top layer of soil before it is doing anything at all, and that watering-in takes days you do not want to be spending after germination has started.

Winter annual pre-emergent timing

Fall Pre-Emergent in Los Angeles, CA

Check the label first on any ground you are seeding this autumn: many pre-emergents can injure new grass. Elsewhere in Los Angeles, CA, if winter annuals are your target, a labeled fall pre-emergent goes down, watered in as its label directs, before about October 28 in a typical year — the median date shallow soil cools through ~70°F and winter annuals start germinating. The ~65°F median, germination well underway, is November 14: 17 days later, a distance between two medians rather than a margin any one autumn gives you.

First: are you seeding this autumn?

Settle the seeding question before you look at a fall pre-emergent date. Many pre-emergents can injure seedlings or prevent grass from establishing. Virginia Cooperative Extension states it plainly in its fall lawn care guidance: if you are planning a fall planting, these materials "will also prevent cool-season turfgrass seed germination". NC State says the same of the fall application for annual bluegrass — it "will prevent any reseeding of tall fescue and other cool-season grasses". Those warnings describe the usual conflict with conventional fall preventers.

Whether treatment and seeding fit in sequence is the exact product label's answer. An at-seeding product is not necessarily a substitute for the usual fall Poa annua prevention program, as explained below. The exclusion follows the treated ground rather than the property line: an area you are not seeding can still be treated.

The autumn seeding conflict looks different around Los Angeles, CA, because the cool-season renovation is not the local job: on warm-season turf, establishment work — seeded bermuda, sod, sprigs, plugs — belongs to late spring and early summer, not to autumn. What that means for this page is that the October 28 crossing has to be scheduled around any establishment still going in, rather than the other way about, and around the one autumn seeding job the South does have.

Los Angeles, CA is also a winter-overseeding market — ryegrass sown over dormant warm-season turf for color through the winter. That job is triggered by the base lawn shutting down as soil falls through about 70°F, which is the same reading that starts winter annuals germinating. One soil temperature, two jobs, and a pre-emergent can prevent the ryegrass from establishing. If you follow the winter-overseeding link below you will find a different date for that crossing: the two datasets read the same threshold under different rules — this one requires the crossing to hold for 14 days, the older one takes the first dip — and re-deriving the older set is tracked separately. Same climate, same temperature, two conventions for calling it.

If you have already applied a pre-emergent, or are about to, the wait before seed can go down is the part people get wrong.

Most conventional pre-emergents can injure seedlings or prevent establishment. Before seeding treated ground, follow the exact product's reseeding interval for the rate used; waits are often months, not weeks. Before treating newly seeded grass, follow its separate waiting, mowing and establishment requirements. Use a product at seeding only when its label allows your grass species, seed mixture, rate and timing. For crabgrass prevention while seeding cool-season grass, mesotrione products with new-seeding directions are an option only for the existing turf and seed mixture that product lists. Species and timing differ by product, especially for fine fescue; avoid over-application, particularly with perennial ryegrass.

For a ryegrass overseed, check both the existing warm-season turf and the grass you are sowing against the exact product label. A permitted use on one does not establish tolerance on the other. Some labels permit a sequence before winter ryegrass seeding, subject to regional, rate, seed-mixture and establishment conditions. Follow the separate new-turf directions after emergence.

Winter overseeding dates for Los Angeles, CA →

If you are not seeding: the window in Los Angeles, CA

Median soil crossing: October 28; Soil cooling through ~70°F — the barrier goes down before this, not on it. Observed range: October 12 – November 17.
Germination underway: November 14; Soil at ~65°F on a 7-day average — past this a pre-emergent is late for what is already up.
Between the dates: 17 days; Opening median to germination median — two separately summarized dates, not a typical year's interval. Zone 10.

Typical fall pre-emergent dates for Los Angeles, CA, not a forecast: the median crossing over the 2016–2025 shallow-soil record, with the observed earliest and latest years beside it. The threshold was crossed in 10 of the ten years sampled — only a year that crossed can count toward a median. A shaded or irrigated yard cools sooner than a bare south-facing one, so let a soil thermometer have the final say. Rates, intervals and the maximum you may apply in a year are on your product's label, which is the legal authority.

Los Angeles, CA’s autumn, in numbers

Across the ten years of shallow-soil records behind this page, Los Angeles, CA's 7-day soil average first fell to and stayed at or below ~70°F on October 28 in a median year. Soil reaches ~65°F around November 14, 17 days later. Both are medians over the years each threshold was actually crossed, which need not be the same years, so that is the distance between two published medians rather than a margin any one autumn gives you. The free reminder is anchored to that same median for properties whose ZIP starts 900, 902 and 906 — the prefixes this dataset covers for Los Angeles, CA: it reads no weather at all and has two send dates off this page's number: one a week ahead that says to apply and water in — ahead of this date, as this page advises — and one on October 28 itself as a backstop if it isn't down yet. It fires on whichever of those dates you already have the alert switched on for, so enabling it late means one send or none rather than two. A ZIP curated to a different metro is anchored to that metro's median instead of Los Angeles, CA's; only a ZIP this dataset does not curate at all falls back to the forecast path, which fires at most once.

The fall pre-emergent window is not a fixed date. In Los Angeles, CA the crossing has landed anywhere in October 12 – November 17 — a span of 36 days. Over a month of movement, October 12 and November 17 being the two ends of it. A fixed calendar date in Los Angeles, CA sits somewhere inside that span, and the record behind this page holds the span rather than a year-by-year account of where it landed.

Observed range of the crossing
Median crossing (October 28)
Germination underway (November 14)

The 2016–2025 modeled shallow-soil record for Los Angeles, CA — 10 years in which the opening crossing was observed. No autumn seeding window is plotted: this metro has none this page is willing to derive.

Let the next date come to you instead

Los Angeles, CA's own median lands around October 28 (observed range October 12 – November 17), with germination typically underway by November 14 — bookmarking this page won't move with it. A seasonal reminder for your own ZIP does, for whatever's actually next on your calendar.

We'll email you about three weeks before this ZIP's normal first freeze — while irrigation contractors still have slots, and before the backflow preventer is the part that freezes.

Your ZIP code

The blow-out reminder counts back from your metro's NOAA 1991–2020 median first freeze, not this year's forecast — a normal year, give or take a couple of weeks. Add your address and the reminder follows the live forecast for your own yard, with the checklist built around the zones and shut-offs you've mapped.

One application here, or two?

Before any interval: whether a second pre-emergent application is permitted at all is a property of the product, not of Los Angeles, CA and not of the October 28 crossing above. Some pre-emergents are a single application for the year, and where two are allowed the interval and the combined ceiling are both on the label. What follows is what extension services publish for each kind of lawn — useful for recognizing which pattern you are being shown, and not a schedule to follow before you have a product in hand.

Los Angeles, CA sits in zone 10, and for that zone the schedule catalog is mostly warm-season: it rates 7 warm-season grasses — Bermuda, Zoysia, St. Augustine, Bahiagrass and others — against no cool-season one at all. Clemson's bermudagrass and zoysiagrass maintenance calendars both put a pre-emergent down in September "with a second application 8 to 10 weeks later", and its warm-season weed guidance gives the interval as "eight or nine weeks after the first" for season-long control. UGA gives the reason rather than just the number: "A second application can be applied in winter to control later germinating plants."

What makes a second fall pre-emergent application a question at all is how long germination runs. University of Tennessee Extension puts it in months rather than weeks: once soil temperatures fall below 70 degrees F, "germination of annual bluegrass seeds will begin and continue for the next 2-3 months". Measured from Los Angeles, CA's own crossing on October 28, that runs to somewhere around December 27 – January 26. Whether the product you choose holds that long is a property of the product, and it is on the label.

Whichever published pattern applies, a pre-emergent split is a DIVISION of one year's allowance and not an addition to it. Penn State Extension is explicit that where more than one pre-emergence application is made in a season, "most product labels recommend using rates lower than the maximum annual application rate for each of the two applications". Kansas State describes the same thing as a half rate each time. NC State's entries for prodiamine products record that the maximum yearly rate differs by turf species, and that a label can cap the active ingredient over any 12-month period rather than per calendar year — which is how a fall application and the following spring's can come out of one allowance. This page states no rate for exactly that reason: which product, at what rate, how many times and how far apart are all label questions, and as Clemson puts it, the label is the law.

Autumn and spring are one program

The other half of the pre-emergent program is the spring application, and it is the half Los Angeles, CA cannot put a date on: in most years on record soil here does not go cold enough over winter to produce a clean warming crossing for crabgrass, so the sibling page for this metro publishes no median spring date. The fall crossing above has one and the spring half does not — which makes the yearly total the thing to watch rather than the interval between them, because a label's ceiling applies whether or not the second application has a date to hang off.

Spring pre-emergent timing in Los Angeles, CA →

The national calendar, set against Los Angeles, CA

Ranked by median opening date, Los Angeles, CA is the 70th earliest of the 83 metros here that have a crossing to rank. That puts Los Angeles, CA among the latest quarter of the metros we publish. Labor Day falls at least 51 days before this metro's median crossing, and at least 35 days before the earliest crossing on file here. Whether a product applied then is still working when the soil cools is a label question — the warm-season calendar quoted below starts in September on purpose. For scale: Duluth, MN opens the national ordering on July 30 and Tampa, FL closes it on November 27, and this crossing falls 90 days after the first and 30 days before the last.

The metros that open just before Los Angeles, CA are El Paso, TX (October 26), then Jackson, MS (October 19); just after it come Las Vegas, NV (October 29), then San Diego, CA (October 29). Dallas, TX (1,232 miles away) crosses on the same day as Los Angeles, CA despite the geography, which is a reminder that this is a soil measurement and not a latitude. The median is not the whole of what the record holds — the observed ranges are Los Angeles, CA's October 12 to November 17, Dallas's October 15 to November 8.

Inside California the fall pre-emergent window is not uniform. We publish Fresno, CA (October 17), Sacramento, CA (October 14), San Diego, CA (October 29), San Francisco, CA (August 24), Tahoe City, CA (August 7), and the furthest from Los Angeles, CA is Tahoe City, CA, 82 days earlier. That is the distance between two published stations in one state, not a figure for any yard between them — and it is why this family publishes per metro rather than per state.

The rule you will meet most often is "apply a few weeks before your first frost". In Los Angeles, CA it has nothing to attach to: a 32°F freeze is rare enough here that NOAA publishes no median date for one. The soil record does carry a date here — the October 28 crossing above — so that is what this page times from, rather than a frost that has no normal to quote.

Before the fall pass in Los Angeles, CA

When should I apply a fall pre-emergent in Los Angeles, CA?: In a typical year a fall pre-emergent in Los Angeles, CA goes down before October 28 — the median date the city's shallow soil cools to and stays at or below ~70°F on a 7-day average, which is when winter annuals start germinating. The barrier has to be down and watered in ahead of that, not on it. Because the date has ranged October 12 – November 17 across the record, read a soil thermometer rather than applying on the same weekend each year.
Can I apply a fall pre-emergent and overseed in the same autumn in Los Angeles, CA?: Pairing a fall pre-emergent with overseeding depends on the exact product and when you seed. Do not assume an earlier application has cleared. Many pre-emergents can injure new grass, so on an area you are seeding any overlap needs product-specific label permission. At-seeding use needs explicit label permission for the species, mixture, rate and timing. Most conventional pre-emergents can injure seedlings or prevent establishment. Before seeding treated ground, follow the exact product's reseeding interval for the rate used; waits are often months, not weeks. Before treating newly seeded grass, follow its separate waiting, mowing and establishment requirements. Use a product at seeding only when its label allows your grass species, seed mixture, rate and timing. For crabgrass prevention while seeding cool-season grass, mesotrione products with new-seeding directions are an option only for the existing turf and seed mixture that product lists. Species and timing differ by product, especially for fine fescue; avoid over-application, particularly with perennial ryegrass.
Is it too late for a fall pre-emergent in Los Angeles, CA?: Whether a fall pre-emergent is too late in Los Angeles, CA turns on germination, not a date on a calendar. Once soil there is past ~65°F — typically around November 14 — this season's winter annuals are coming up, and a pre-emergent cannot touch a plant that has already emerged. Germination runs for weeks rather than finishing in a day, so an application just past that line still catches the stragglers; well past it, the honest answer is a post-emergent option now and an earlier start next year.
Does one application cover the whole season in Los Angeles, CA?: Whether one fall pre-emergent application covers the whole season depends on the product, not on Los Angeles, CA — though locally, germination runs from the October 28 crossing to roughly December 27 – January 26 on University of Tennessee Extension's two-to-three-month figure. The section above sets out which pattern extension publishes for which grass, and the constraint underneath both: a split divides one year's labeled allowance rather than adding to it. Your label decides.
Does my USDA zone tell me when to apply in Los Angeles, CA?: A USDA hardiness zone does not set fall pre-emergent timing in Los Angeles, CA, and this page's dataset shows that rather than asserting it. Los Angeles, CA is zone 10, and the 3 zone-10 metros in this dataset spread 66 days apart on their own crossings — from San Francisco, CA on August 24 to San Diego, CA on October 29. A hardiness zone measures average winter cold, not how fast shallow soil gives up its summer heat in autumn, so latitude, elevation and how maritime the climate is all move the crossing inside one zone band — which is why this page is built on Los Angeles, CA's own soil records. What the zone does place is the catalog: which grasses are rated viable at zone 10, and so which of the two published patterns this page leads with. Which one applies to your lawn is settled by what is growing in it, not by the band and not by this page.
Does Poa annua matter in a dormant lawn in Los Angeles, CA?: A dormant lawn is where Poa annua shows worst. A warm-season lawn going straw-brown for the winter turns every patch of bright green annual bluegrass into a feature, and the same plants then compete with green-up in spring before dying out in the heat. Clemson groups it with chickweed, henbit and purple deadnettle as winter annuals that "germinate in the fall, grow through the winter, set seed, and die as temperatures rise in early summer" — which is why the fall barrier is the point of intervention rather than a spring rescue.
How far apart are Los Angeles, CA's two published dates?: Los Angeles, CA's two published fall dates are 17 days apart: soil crosses ~70°F around October 28 and reaches ~65°F around November 14. Both are medians over the years each threshold was actually crossed, so that is the gap between two medians and not a measurement of a typical autumn. Aim to be finished before the front of it rather than inside it — a pre-emergent needs rain or irrigation to move it into the top layer of soil before it is doing anything at all, and that watering-in takes days you do not want to be spending after germination has started.