Spring Weed Control: Soil Temp, Not the Calendar

Spring is when the entire year’s weed battle is won or lost. The weeds you see in June germinated in March — and the cheapest, most effective weapon you have is a properly timed pre-emergent barrier that stops them before they ever surface.

In New Mexico, that window is specific: Crabgrass and summer annual pre-emergent as soil holds 55°F at 2 inches — February to early March in the southern valleys, April to May in the north. The state spans two months on this decision. Miss it and you'll be fighting Crabgrass in irrigated turf and Puncturevine — goathead, the signature southwestern hot-dry-ground annual and a tyre and bare-foot problem as much as a turf one with post-emergents all summer.

Why Spring Weeds Happen

Weed control is one job inside a larger spring sequence — if you want the whole order of operations, start with our spring lawn care guide and come back here for the herbicide timing.

Weed seeds are patient. A single crabgrass plant drops up to 150,000 seeds that sit dormant in your soil all winter, waiting for one trigger: soil temperature. Texas A&M puts that trigger lower than most homeowners expect. Their guide times pre-emergence applications to soil “between 50 and 55 °F”, and names that as “the soil temperature range in which several summer annual weeds — including crabgrass (Digitaria spp.) — begin to germinate.” So the barrier belongs in the ground at 50°F, not at 60: by the time the top inch holds 55 you are at the end of the window rather than the start, and germination is usually two to three weeks ahead of anything you can see.

Thin turf accelerates the problem. Every bare patch is unfiltered sunlight reaching the soil surface, and sunlight on bare soil is a germination invitation. That’s why the best long-term weed control is a dense lawn — in New Mexico, that means healthy Bermuda.

Identifying Your Spring Invaders

The treatment depends entirely on what’s coming up:

• Grassy weeds (crabgrass, dallisgrass, goosegrass) — lighter green, wider blades, grow in clumps that fan outward. Pre-emergent is your primary defense.
• Broadleaf weeds (dandelion, clover, henbit, chickweed) — anything with leaves that don’t look like grass. Most respond to selective post-emergents.
• Sedges (yellow and purple nutsedge) — triangular stems that grow faster than surrounding turf. Standard herbicides won’t touch them; they need sedge-specific chemistry — halosulfuron or sulfentrazone are the common two, and UF/IFAS also lists imazaquin and penoxsulam.

New Mexico Lawn Threat Matrix

What to scout for on Bermuda lawns in USDA zones 4b–9a.

High-Risk Weeds

• Crabgrass in irrigated turf
• Puncturevine — goathead, the signature southwestern hot-dry-ground annual and a tyre and bare-foot problem as much as a turf one
• Field bindweed
• Kochia and Russian thistle at the dry margins
• Khakiweed and spurges in thin, hot, compacted ground
• Bermudagrass encroaching into a northern bluegrass lawn, which is the transition zone working against you
• Annual bluegrass (Poa annua) in over-irrigated cool-season turf

High-Risk Diseases

• Iron chlorosis — not a pathogen, but the most common reason a New Mexico lawn is yellow, and the one where buying the wrong chelate wastes the money entirely
• Salinity injury from irrigation water and from salts accumulating above caliche, which reads as drought stress that watering does not fix
• Spring dead spot on bermudagrass, appearing as the lawn greens up
• Summer patch and other root-zone diseases on cool-season lawns in the north
• Dollar spot
• Large patch on zoysia as soil passes through the 70s

Common Pests

• White grubs from May and June beetles and masked chafer
• Chinch bugs in hot dry sandy strips, which describes most of the state
• Bermudagrass mites in the south
• Sod webworm
• Cutworms and armyworms in monsoon years
• Bluegrass billbug in the northern cool-season lawns
• Red imported fire ants in isolated instances only, with Dona Ana County under quarantine: nursery stock, sod, soil, baled hay and straw, and soil-moving equipment leaving the county must be certified free of the pest

The Spring Weed Control Plan

Product Recommendations

The cheapest item here is the one that decides whether the others work, because every date on this page is really a temperature:

Preventing Next Year’s Weeds

Everything on this list makes next spring easier:

1. Feed appropriately — a dense, well-fed lawn out-competes weeds naturally. Follow the New Mexico window — New establishment gets 0.5 to 0.75 lb of nitrogen per 1,000 sq ft every other week for six to eight weeks. After that the calendar follows the grass, not the state: cool-season lawns in the north feed spring and autumn, warm-season lawns in the south feed through the warm months and stop well before dormancy.
2. Water deeply, infrequently — shallow daily watering breeds shallow-rooted turf and happy weeds.
3. Sharpen your mower blade — torn grass tips brown out and thin the canopy.
4. Fall pre-emergent — winter annuals like henbit and chickweed germinate in fall. A September/October application stops the weeds you’d otherwise see next February — but check the interval first if you also plan to seed, because pre-emergent and seed work against each other.

If slender clumps stand above the turf two days after you mow and the mower smells of onion, that is a different plant on a different calendar — wild onion and wild garlic are treated in autumn and February, not in spring when you notice them.

For the mechanism behind the dates above — soil temperature depth, growing degree days, and why full forsythia bloom is the go signal rather than the warning — see when to apply pre-emergent.