Manchester
Treat broadleaf51°F↑ warming
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 1 – Oct 20
New Hampshire Weed Watch · updated Nov 3, 1:18 AM CT
When to apply pre-emergent in New Hampshire
Live soil temperatures for Manchester, Concord and Portsmouth, updated every three hours. Weeds sprout by soil temperature, not by the calendar, so the right week moves from year to year.
In New Hampshire, pre-emergent is a spring job: it stops crabgrass. Fall is seeding season here, so fall weed control means treating broadleaf weeds instead.
Spring pre-emergentNext season
Typically Apr 23 – May 16
Stops crabgrass and other summer weeds before they sprout.
Fall: no pre-emergentThis season
Treat broadleaf weeds Sep 1 – Oct 28
Fall is seeding season here, and pre-emergent would stop grass seed too.
Right now · fall (seeding season)
Treat broadleaf weeds now across New Hampshire
Soil is 48–52°F now. In fall, dandelions, clover and creeping Charlie pull sugars — and weed killer — down to their roots. Seeding this fall? Skip pre-emergent; it stops grass seed too.
Soil temperature by city
Soil 2 inches down, 5-day average: solid line = the last two weeks, dashed = the six-day forecast.
Concord
Treat broadleaf48°F↑ warming
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 1 – Oct 17
Portsmouth
Treat broadleaf52°F↑ warming
Fall is the best time to treat dandelions and clover: they pull weed killer down to their roots.
Broadleaf window Sep 1 – Oct 28
New Hampshire pre-emergent calendar
Spring pre-emergent stops crabgrass. The window runs from the typical day soil warms to 50°F to the day it holds 55°F, when crabgrass starts germinating (2016–2025). In fall New Hampshire lawns are in seeding season, so there is no fall pre-emergent; the window shown is for treating broadleaf weeds instead, from September until two weeks after soil usually cools to 55°F.
| City | Spring pre-emergent (crabgrass) | Fall (seeding season) |
|---|---|---|
| Manchester | Apr 23 – May 14 | None (seeding season) · treat broadleaf Sep 1 – Oct 20 |
| Concord | May 3 – May 16 | None (seeding season) · treat broadleaf Sep 1 – Oct 17 |
| Portsmouth | May 2 – May 16 | None (seeding season) · treat broadleaf Sep 1 – Oct 28 |
These are typical-year dates (the median of 2016–2025); any one year can run a couple of weeks earlier or later, which is what the live readings above are for. For your exact yard, check soil temperature by ZIP.
What people in New Hampshire are identifying
We record the state each identification comes from. New Hampshire's list appears here once it has at least 40 identifications spread over 7 or more days — so no single scan stands out. Until then, see the national list, or add yours:
Identify a weed from a photoWeeds to watch in New Hampshire this fall
Questions about New Hampshire
When should I apply crabgrass pre-emergent in New Hampshire?
Put crabgrass pre-emergent down as soil warms to 50°F, before it holds 55°F and crabgrass starts germinating. In a typical year (2016–2025) that window is Apr 23 – May 14 in Manchester; May 3 – May 16 in Concord; May 2 – May 16 in Portsmouth.
Should I put down pre-emergent in the fall in New Hampshire?
Usually not. Fall is the best time to seed a cool-season lawn in New Hampshire, and pre-emergent stops grass seed as well as weeds. Fall is the time to treat broadleaf weeds such as dandelion, clover and creeping Charlie, once the summer heat breaks and while they are still growing.
What is the soil temperature in New Hampshire right now?
As of Nov 3, 1:18 AM CT: Manchester 51°F, Concord 48°F, Portsmouth 52°F (5-day average, about 2.4 inches down). Treat broadleaf weeds now across New Hampshire.
How the readings and dates are made, and their limits: Weed Watch method. Soil data: Open-Meteo.com (CC BY 4.0); typical dates: NASA POWER.