Weed Control
Black Medic: Identification and Control in Lawns
Quick answer
Black medic is a yellow-flowered legume that fixes its own nitrogen, so it takes over lawns that are underfed and dry. Feeding nitrogen, watering deeply and mowing high remove its advantage. A three-way broadleaf herbicide handles the plants that are already there.
Black medic is usually mistaken for clover, and the two do tell a similar story. Both are legumes with nitrogen-fixing root nodules, which means both thrive where the grass is short of nitrogen and neither is much troubled by poor fertility. If you have black medic, the lawn is hungry.
The identification difference is worth learning: black medic has yellow flowers and its middle leaflet sits on a short stalk, while white clover has white flower heads and three leaflets attached at the same point. Set your feeding rate with the fertilizer calculator before deciding this is a spraying problem.
On this page
How do I identify black medic?
| Trait | Black medic |
|---|---|
| Weed type | Broadleaf, in the legume family |
| Life cycle | Summer annual, occasionally behaving as a short-lived perennial |
| Season | Warm season; most visible from late spring through summer |
| How it spreads | Seed, from pods that turn black as they ripen |
| Leaf | Three oval leaflets with the middle one on a short stalk, unlike clover where all three attach at one point |
| Flower | Tight clusters of tiny bright yellow flowers, roughly a quarter inch across |
| Seed pod | Small tightly coiled pods that ripen from green to black, the source of the name |
| Roots | A taproot with nitrogen-fixing nodules, letting it grow where turf is starved |
| What it says about the lawn | Low nitrogen, dry soil, compaction and thin turf |
Yellow woodsorrel also has yellow flowers but heart-shaped leaflets and upright pods that fling seed. White clover has white flowers and a pale watermark on oval leaflets.
Why do I have black medic in my lawn?
Because the turf is not getting what black medic does not need. As a legume it carries nitrogen-fixing bacteria in root nodules and manufactures its own supply, so when soil nitrogen runs low it keeps growing while the grass slows. Every thin, hungry patch is an opening.
Drought and compaction add to it. The taproot reaches moisture that shallow turf roots miss, so black medic stays green and spreading while unwatered grass browns out in summer. Mowing low makes it worse again, since the sprawling stems run below blade height.
Feed on a real program rather than a single spring application, water deeply and less often, and mow at the top of the range for your grass. Rates for common products are in the fertilizer rate chart, and a soil test tells you whether pH is blocking the nutrients you are already applying, covered in how to test soil pH.
What kills black medic in a lawn?
It is easier to remove than clover and easier still to prevent. The order is fertility, then density, then herbicide for what remains.
| Method | When | What it involves |
|---|---|---|
| Feed nitrogen | Through the season, most in fall | Removes the advantage a nitrogen-fixing legume has over starved turf. The control that lasts. |
| Water deeply, less often | Summer | A taprooted weed beats shallow-rooted turf in drought, so letting the lawn go dormant hands it ground. |
| Raise mowing height | Every mowing | Shades the sprawling stems that run below the blade at low cuts. |
| Hand pulling | Moist soil, small infestations | The taproot lifts reasonably well when soil is wet, and plants do not regrow from fragments the way creeping perennials do. |
| Three-way broadleaf herbicide | Spring or fall, on actively growing plants | Mixes with 2,4-D, dicamba and mecoprop control black medic well. |
| Overseed thin areas | Late summer to early fall | Closes the bare ground its seed needs and keeps the fix in place. |
| Soil test | Before a third fertilizer purchase | If feeding is not working, pH or a nutrient other than nitrogen may be the limit. |
Black medic is an annual in most lawns, so plants die at frost. The seed bank is what returns, which is why fertility and density matter more than late-season spraying.
Which products work on black medic?
On the fertility side, Jonathan Green Green-Up Lawn Food 29-0-3, 15,000 sq ft covers 15,000 sq ft, The Andersons Core 24-6-12 Professional Lawn Fertilizer, 45 lb covers 15,500 sq ft with quick and slow release nitrogen plus iron, and Milorganite Slow-Release Nitrogen 6-4-0 Fertilizer, 5 lb Bag (4-Pack) is a low-salt slow-release option the maker says feeds for 8 to 10 weeks without watering in, which suits hot, dry stretches when burn risk rises.
For the plants already present, Ortho WeedClear Weed Killer for Lawns Concentrate, 1 gal lists over 250 broadleaf weeds and covers up to 64,000 sq ft, and Spectracide Large Plot Weed Stop for Lawns Concentrate, 1 gal is the lower-cost equivalent. If feeding has not thickened the lawn as expected, MySoil Soil Test Kit reports pH and 13 plant-available nutrients in 6 to 8 days, and Luster Leaf Rapitest Soil Test Kit, 40 Tests is the cheap at-home alternative for quick pH checks.
What gear helps with black medic?
A spreader for the feeding program, a soil test to confirm what is short, and a sprayer for the plants that are already established. Spreader options are in the best lawn spreaders.
Scotts Turf Builder EdgeGuard DLX Broadcast Spreader
$94.97A pre-calibrated push broadcast spreader holding up to 15,000 sq ft of product, with an edge shield to keep granules off pavement and beds.
Best for: lawns up to about a third of an acre
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Jonathan Green Green-Up Lawn Food 29-0-3, 15,000 sq ft
$73.27A 29-0-3 maintenance fertilizer sized for 15,000 sq ft that pairs with a matching seed program.
Best for: established cool-season lawns
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MySoil Soil Test Kit
$34.26A prepaid mail-in lab test reporting pH and 13 plant-available nutrients in 6 to 8 days with product and rate recommendations.
Best for: testing before buying more fertilizer
Check price on AmazonHow we chose
We did not test these products in person. Picks are researched from manufacturer specifications and owner manuals, engine and safety certifications where they apply, warranty terms, public recall records, and the recurring themes in verified owner reviews. We favor established brands with large review counts and parts support, match each pick to a real yard size or task, and place it in the tier where its price and capability actually belong.
Frequently asked questions
Is black medic the same as clover?
No, though both are legumes that fix their own nitrogen and both signal an underfed lawn. Black medic has bright yellow flower clusters, a middle leaflet on a short stalk, and coiled pods that ripen black. White clover has round white flower heads, three leaflets attached at one point, and a pale watermark on each leaflet. Control is similar, with feeding as the foundation.
Does black medic mean my lawn needs fertilizer?
Usually yes. As a legume it manufactures its own nitrogen through root nodules, so it competes best exactly where the grass is starved. A lawn with widespread black medic is generally underfed, often dry, and sometimes compacted as well. Feed on a real program, water deeply and less often, and mow high, then treat any remaining plants rather than spraying first.
Will black medic die on its own?
In most lawns it behaves as a summer annual and dies at frost, though it can persist as a short-lived perennial in some conditions. The plants going away does not solve anything, because the seed bank returns the following year into the same thin, hungry ground. Changing the fertility and density is what stops the cycle rather than waiting it out.
Researched, not professional advice. This page is compiled from published specifications, manuals, labels and owner-review consensus, not hands-on testing. Follow the manufacturer's instructions and product label, and consult a qualified professional where safety, chemicals, fuel or structures are involved. As an Amazon Associate we earn from qualifying purchases.