How to Get Rid of Crabgrass: 55°F Timing Tip
Kelly Smith Trimble brings practical gardening knowledge and experience explaining how plants grow and thrive. Her interests include vegetable growing, seasonal garden care, and the everyday decisions that help gardeners make the most of their outdoor spaces.
Quick answer
Pull young crabgrass plants before they drop seed. Then use a pre-emergent herbicide when spring soil hits 55°F to stop next year's crop. Pre-emergent is a weed killer that blocks seeds before they sprout. Mow at the right height and water deeply to grow thick grass. Dense grass crowds out crabgrass on its own over time.
Identify Crabgrass Before You Act
Treating the wrong plant wastes time and money. Crabgrass is a summer annual — it sprouts from seed each spring, spreads through the season, and dies at the first frost. Two species are common in US lawns: smooth crabgrass (Digitaria ischaemum) and large (hairy) crabgrass (Digitaria sanguinalis).
Key traits to look for, according to UC IPM:
- Growth habit: Low, spreading clumps that root at stem nodes touching the soil.
- Leaf color: Seedling leaves are light green — noticeably paler than surrounding turf.
- Smooth crabgrass leaf blade: ¼ to ⅓ inch wide, up to 5 inches long, smooth on top with possible hairs below.
- Large crabgrass leaf blade: 0.2–0.6 inches (5–15 mm) wide with hairs on both surfaces (NC State Extension).
- Flower stalk: 3–11 finger-like branches radiating from near the top of the stem.
- No rhizomes or stolons: Unlike bermudagrass (which has underground rhizomes and aboveground stolons) and dallisgrass (short thick rhizomes), crabgrass spreads only by seed.
| Feature | Crabgrass | Bermudagrass | Dallisgrass |
|---|---|---|---|
| Life cycle | Summer annual | Perennial | Perennial |
| Spreads by | Seed only | Rhizomes + stolons | Rhizomes + seed |
| Flower branches | Spaced ⅛–¼ in apart near stem tip | Originate at same point | Widely separated on stem |
| Leaf surface (large sp.) | Hairy both sides | Smooth to sparse | Smooth |
If you are unsure whether you have crabgrass or a perennial grassy weed, check for rhizomes by gently pulling a plant. Crabgrass roots cleanly with no underground runners attached.
Why Crabgrass Keeps Coming Back
One large crabgrass plant can produce up to 150,000 seeds in a single season, and those seeds stay viable in the soil for at least 3 years. When the plant dies in fall, it leaves a bare patch — exactly the open, warm soil crabgrass seeds need to germinate the following spring. This cycle repeats until you break it at two points: stop new seeds from forming this season, and block germination next spring.
Crabgrass is also a symptom of a stressed lawn, not the original problem. It thrives in thin, overwatered, or underfertilized turf. A dense, healthy lawn shades the soil and physically crowds out crabgrass seedlings before they can establish.
Step-by-Step Removal Plan
Step 1 — Pull or Hoe Before Seed Drop (Do This Now)
Hand-pulling is the safest and most immediate control, especially in garden beds. Pull plants when they are young and the soil is moist. The goal is to remove them before the seed heads mature. Once a plant has set seed, pulling it still helps but seeds may already be in the soil.
- In ornamental beds: pull or hoe young plants, then apply mulch immediately to block light from remaining seeds.
- In lawns: pull isolated plants by hand. After mowing a crabgrass-infested area, clean the mower deck thoroughly to avoid spreading seeds to other parts of the yard.
- Do not compost seed-bearing crabgrass — bag and discard it.
Step 2 — Mulch Garden Beds
In raised beds and landscape areas, mulch blocks the sunlight crabgrass seeds need to germinate. According to UC IPM, coarse mulch (wood chips, nuggets) should be 3 to 6 inches deep; finer mulch (shredded bark, composted yard waste) needs 2 to 3 inches. Replenish mulch as it decomposes, and rake it occasionally — old, decomposed mulch can itself become a germination medium for weed seeds.
Step 3 — Apply Pre-Emergent Herbicide in Spring
A pre-emergent herbicide — one applied before seeds sprout — is the most effective chemical tool for lawn crabgrass. It does not kill existing plants; it prevents germination. Timing is everything.
The trigger: Both crabgrass species begin germinating when soil temperatures reach 55°F for several consecutive days (UC IPM). NC State Extension reports germination in North Carolina between 53 and 58°F measured at a 4-inch depth, typically March through early May. Apply the pre-emergent a few weeks before your local soil hits that range.
How to find your soil temperature: many county Extension offices and university weather networks publish real-time soil temperature maps. A soil thermometer at a 4-inch depth works too.
How to apply:
- Choose a product labeled for your specific turf type — always read the label, which is a legal requirement under federal pesticide law (FIFRA). Manufacturers may have a sales interest in their products, so cross-check with your local Extension office.
- Apply uniformly across the lawn.
- Water in with approximately ½ inch of water soon after application to activate the herbicide in the soil.
- You can time the application before a forecasted rain event instead of irrigating manually.
Stop condition — overseeding: Pre-emergent herbicides also inhibit desirable grass seed. Do not overseed or reseed bare patches until the herbicide is no longer active. The product label will state the waiting period — follow it exactly.
Stop condition — vegetable gardens: Do not use pre-emergent or post-emergent herbicides in vegetable gardens. The same chemistry that harms crabgrass can damage food crops.
In regions with long crabgrass seasons (6 to 8 months in parts of California, per UC IPM), a second pre-emergent application may be needed for extended control. The label will specify whether a second application is permitted.
Illustrative example (checked arithmetic): Suppose your lawn is 2,000 sq ft and a pre-emergent product is labeled at a rate of X oz per 1,000 sq ft — you would apply 2X oz total. Always use the rate printed on your specific product label; rates vary by active ingredient and formulation. This example is illustrative only to show how to scale from label rate to your lawn size.
Step 4 — Fix the Lawn Conditions That Invited Crabgrass
Chemical control alone will not solve a recurring crabgrass problem. The real fix is a dense, vigorous lawn that shades the soil and outcompetes crabgrass seedlings. Three practices matter most:
Mowing height: Mowing too short creates bare patches. UC IPM recommends these species-specific heights:
| Grass species | Mowing height (inches) |
|---|---|
| Creeping bentgrass | Under 0.5 |
| Kentucky bluegrass | 1.5–3.0 |
| Tall fescue | 2.0–3.0 |
| Annual ryegrass | 1.0–3.0 |
| Perennial ryegrass | 1.0–3.0 |
| Common bermudagrass | 1.0–2.0 |
| Hybrid bermudagrass | 1.0–2.0 |
| St. Augustinegrass | 2.0–3.0 |
| Zoysiagrass | 1.0–2.0 |
| Buffalograss | 2.0–unmowed |
Never remove more than one-third of the leaf blade in a single mowing. If your lawn is currently shorter than the recommended range, raise the mowing height gradually over several cuts. Choosing the right grass species for your region also affects how competitive your turf can be against weeds.
Watering: Shallow, daily irrigation encourages shallow roots and weak turf — exactly what crabgrass exploits. Water deeply to a 6 to 8-inch soil depth and less frequently. This builds deeper roots and a denser canopy. For guidance on timing, see when to water grass for best results.
Fertilization: An underfertilized lawn is thin and vulnerable. UC IPM states that most lawns need 4 to 6 pounds of actual nitrogen per 1,000 square feet per year, split across 4 to 6 applications. Fertilize when your turf species is actively growing — cool-season grasses in fall and spring, warm-season grasses in late spring through summer. A complete fertilizer (containing nitrogen, phosphorus, and potassium) is recommended at least once a year, typically in spring.
Illustrative nitrogen example (checked arithmetic): A 5,000 sq ft lawn at the midpoint rate of 5 lb actual nitrogen per 1,000 sq ft per year needs 25 lb of actual nitrogen annually (5,000 ÷ 1,000 × 5 = 25 lb). Split across 5 applications, that is 5 lb of actual nitrogen per application. Check your fertilizer bag’s guaranteed analysis to calculate how many pounds of product deliver that amount of actual nitrogen.
Step 5 — Overseed Bare Patches After Frost
Once crabgrass dies at the first frost, overseed the bare patches it leaves behind. A dense stand of desirable grass is the best long-term barrier. For timing by grass type, see when to overseed a lawn. Do not overseed while a pre-emergent herbicide is still active — wait until the label’s stated interval has passed.
Home Remedies: What the Evidence Says
Vinegar, salt, and similar household products are sometimes suggested for weed control. Salt applied to soil raises salinity and can damage or kill surrounding desirable plants and soil organisms — it is not a targeted or reversible treatment. Concentrated vinegar (acetic acid) can burn foliage on contact but does not kill roots and can lower soil pH. Neither is a safe substitute for mechanical removal or labeled herbicides in a lawn setting.
Solarization for Heavily Infested Beds
If a garden bed is severely infested, soil solarization — covering moist soil with clear plastic for 4 to 6 weeks during the hottest part of summer — can kill crabgrass plants and seeds in the upper soil layer. This works best during periods of high solar radiation and is most practical before replanting a bed, not in an established lawn.
How to Read Your Results and What to Do Next
After pulling plants and applying a pre-emergent in spring, check the treated area once soil temperatures consistently exceed 55°F. If new crabgrass seedlings still appear in scattered spots, those likely germinated before the herbicide was activated or in areas where coverage was uneven. Hand-pull those seedlings immediately — they are easiest to remove before the 3-leaf stage.
If crabgrass returns heavily the following season despite pre-emergent treatment, the underlying problem is almost certainly thin turf. Assess your mowing height, irrigation depth, and fertilization schedule. Bare or brown patches that persist after crabgrass dies in fall are the spots to overseed first. A lawn that fills in densely will shade the soil enough to suppress crabgrass germination without relying on herbicides alone.
Frequently asked questions
Can I apply a pre-emergent herbicide and overseed at the same time?
No. Pre-emergent herbicides prevent seed germination without distinguishing between crabgrass and desirable grass seed. You must wait until the herbicide is no longer active before overseeding. The product label states the required waiting period — follow it exactly, as it varies by active ingredient and formulation.
Will pulling crabgrass spread its seeds around my yard?
It can if the plant has already produced mature seed heads. Pull plants before seed heads form to avoid this. After mowing a crabgrass-infested area, UC IPM recommends thoroughly cleaning the mower deck to avoid transferring seeds to uninfested parts of the lawn.
Does crabgrass come back from the roots after I pull it?
No. Crabgrass is a summer annual with no rhizomes or stolons, so it cannot regrow from root fragments. Any new plants the following season come from seeds already in the soil — which is why preventing seed set this season and applying a pre-emergent next spring are both necessary steps.
How long do crabgrass seeds stay viable in the soil?
According to UC IPM, crabgrass seeds can remain viable in the soil for at least 3 years. This is why a single season of heavy seed production can fuel infestations for multiple years, even if you remove all visible plants. Consistent pre-emergent treatment over several seasons is needed to draw down the seed bank.
Is a 'weed and feed' product a good way to handle pre-emergent timing?
It can be convenient, but UC IPM notes a timing conflict: the best window for crabgrass pre-emergent control (tied to soil temperature) may not align with the best time to fertilize your specific turf species. If the two windows don't match in your area, applying them separately gives you more precise control over each.
Sources
- Crabgrass / Home and Landscape / UC Statewide IPM Program (UC IPM) · ipm.ucanr.edu
- Large Crabgrass | NC State Extension Publications · content.ces.ncsu.edu
- Digitaria - Wikipedia · en.wikipedia.org
Prepared from these references and checked against them. References retrieved October 11, 2026.
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