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Black Medic Guide

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Black Medic Weed Identification Guide

What is Black Medic?

Black medic (Medicago lupulina) is a broadleaf, low-growing weed that can quickly spread and become problematic in lawns, gardens, agricultural fields, and other spaces. While it is typically a summer annual, thriving in the spring and summer, it can sometimes act as a perennial weed in milder climates.

Commonly referred to as black clover, hop medic, or yellow trefoil, black medic is a member of the legume family, sharing similarities with white clover and oxalis (wood-sorrel). Identifying this weed correctly in your yard is essential for effectively managing its growth.

This guide will help you recognize the key features of black medic. Continue reading to learn where and when it grows, how to eliminate it, and steps for preventing future infestations.

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Black Medic, Clover, or Oxalis

How to Distinguish Black Medic from Other Weeds

Black Medic can sometimes be mistaken for white clover, oxalis (wood sorrel), or other similar weeds, but each of these plants has distinct characteristics. Beyond the leaf shape differences, here’s more information to help you recognize Black Medic. Also, check out our identification guides for white clover and oxalis.

Stems
Black Medic stems typically grow flat, spreading horizontally from a central taproot. These stems do not root at the nodes along their length but can interweave to form a clump of Black Medic. The slender, hairy stems can reach up to two feet long and bear green leaves, yellow flowers, and black seeds in the summer.

Leaves
The leaves of Black Medic can help distinguish it from other weeds. Key features include:

  • Green leaves that alternate along the stem.
  • Trifoliate leaves, meaning each leaf is divided into three leaflets.
  • Oval-shaped leaflets with parallel veins and toothed edges.
  • A small spur or tip projection at the tip of each leaflet.
  • The center leaflet is attached with a longer stalk (petiole) than the other two, often differentiating Black Medic from white clover.

Flowers and Seeds
Black Medic reproduces from seeds, which are produced during the flowering process.

The plant produces clusters of small, bright yellow flowers at the end of the stems, typically from April to July. Each cluster contains 10 to 50 pea-shaped flowers. After flowering, the flowers are replaced by small, kidney-shaped seed pods, which turn black as they mature. Each pod contains one seed, and they measure between 1/2" to 1/8" in size.

Roots
Black Medic grows from a deep, branched central taproot that helps it survive in dry conditions.

Through a symbiotic relationship with rhizobium bacteria, Black Medic can fix atmospheric nitrogen into a form that is usable by the plant, enriching the surrounding soil. This ability allows Black Medic to thrive in areas with low nitrogen, often signaling a nitrogen deficiency in the soil.

Recommended Products

For more details on how and when to apply products to eliminate black medic in your lawn, check out our guide on controlling black medic.

Black Medic Weed Inspection Guide

Black medic, also known as hop medic, black clover, or trefoil, is an annual weed that can quickly spread unless actively controlled. It has the potential to take over lawns, gardens, fields, pastures, and other areas.

Learn more about when and where black medic grows so you can take steps to prevent and manage this invasive broadleaf weed.

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When is Black Medic Likely to Appear?

Black medic is typically a summer annual weed that grows from seeds germinating in the spring. In more temperate climates, however, seeds may also sprout in the fall, and it may even act as a perennial in those regions.

Black medic flowers in the spring and summer, generally between April and July. After flowering, it produces pods containing seeds.

Understanding when black medic seeds germinate is crucial for using pre-emergent herbicides to prevent its growth.

Where Does Black Medic Thrive?
Black medic is versatile and can grow in a wide range of environments.

It is commonly found in pastures, fields, gardens, waste areas, and along riverbanks and railroads. Its bright yellow flowers can be spotted along roadsides and paths throughout the U.S. and southern Canada.

Black medic thrives in dry, sunny areas with disturbed soil, particularly in areas left untended. It can grow in compacted soil and is often seen along sidewalks and curbs.

Since black medic can convert atmospheric nitrogen into a usable form, it is capable of growing in low-nitrogen environments. If you notice black medic or other clovers in your lawn, it may indicate a nitrogen deficiency in the soil. Improving soil health, including addressing compaction and nutrient needs, can help prevent black medic from overtaking your lawn.

Once you've identified an unwanted weed in your yard, take a closer look and compare it to the images in our Black Medic Identification Guide to confirm if it's black medic. If you have black medic in your yard, learn how to eliminate it in the next section of our 4-part guide. Click the right arrow below to continue.

Black Medic Weed Control Guide

Choosing the Right Herbicides to Eliminate Black Medic Weeds

Black Medic (Medicago lupulina), a member of the legume family, can quickly become an unwanted weed in lawns, gardens, fields, pastures, and more. Also called hop medic or black clover, this yellow-flowering weed can be effectively controlled through a proper herbicide application and

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Step1 Eliminate Black Medic Weeds in Your Lawn

How to Apply Post-Emergent Herbicides for Black Medic Control

If Black Medic is already growing in your lawn or garden, you will need to apply a selective post-emergent weed killer to remove it. Make sure to choose a post-emergent herbicide specifically labeled for Black Medic control in your application area. Always consult the product label for the correct application rates and instructions for your type of turf.

When selecting the best post-emergent herbicide for Black Medic, consider the following:

  1. Choose an herbicide labeled for Black Medic control: There are many weed killers available, but you should look for a selective broadleaf post-emergent herbicide that targets Black Medic. Some herbicides can be used in lawns, fields, and pastures, while others may be restricted to specific areas.
  2. Pick the right active ingredients: Consider herbicides containing ingredients like 2,4-D, dicamba, MCPP, triclopyr (for cool-season turfs only), or fluroxypyr, which are known to be effective against Black Medic in turfgrass areas.
  3. Ensure compatibility with your turf: Check the product label to confirm that the herbicide is safe for use on your specific turf type. Some herbicides are suitable for a variety of plants, while others are limited to certain turfgrass species. Ensuring compatibility helps prevent damage to desirable plants.
  4. Apply at the right time: The best time to apply the herbicide is when Black Medic is actively growing, typically in late spring to early summer and early to mid-fall. Keep an eye out for the small yellow flowers that indicate new growth.

When applying your chosen herbicide, follow the instructions on the label for mixing and application. Be sure to wear protective gloves, long sleeves, and closed-toe shoes when handling and spraying the product.

Products we recommend for Step 1

Pro Tip

Always check the product label to ensure the herbicide is safe for your lawn. For example, Triclopyr is suitable for cool-season grasses but may damage warm-season turf, while some products like Celsius WG are intended only for warm-season grasses.

Step2 Prevent Future Black Medic Growth

After treating existing Black Medic weeds, it's important to stay ahead of new growth by using a pre-emergent herbicide.

Since Black Medic spreads via seed, the plant produces resilient seeds that can stay viable in the soil for several years. To prevent the emergence of new weeds, apply a pre-emergent weed preventer labeled for Black Medic control in your turf type during the spring before the soil warms enough to trigger seed germination. It's also recommended to apply it again in the fall.

Pre-emergent herbicides containing active ingredients such as dithiopyr and isoxaben have proven effective in preventing Black Medic from growing.

For the best results, our experts recommend specific pre-emergent herbicide products for Black Medic prevention. Check out the suggested products below to help keep this weed from reappearing in your yard.

Products we recommend for Step 2

If you've spotted Black Medic in your lawn before, there are steps you can take to prevent it from coming back next year. Check out our guide on how to stop Black Medic from growing in your yard to learn more. Click the right arrow below to continue reading.

Black Medic Weed Prevention Guide

Adopt a Consistent Lawn Care Routine

If you've noticed Black Medic in your lawn or garden, you might be wondering how to prevent it from coming back. Maintaining a healthy lawn through a consistent lawn care routine is key to keeping weeds at bay.

Also known as hop medic or black clover, Black Medic thrives in dry, compacted soil with low nitrogen. Improving your lawn's overall health through proper fertilization, irrigation, and aeration, along with pre-emergent herbicide applications, can significantly reduce weed growth.

Follow the tips below to ensure your lawn stays healthy and to prevent Black Medic from returning.

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Step1 Ensure Proper Fertilization for Your Lawn

How to Apply Granular Lawn Fertilizer

Black Medic and other legumes, like white clover, have the ability to fix their own nitrogen, which is why these low-growing weeds often thrive in areas with insufficient nitrogen levels. To prevent Black Medic from taking root in your turf, the key is to follow a fertilization plan that ensures your soil receives the correct amount of nitrogen.

Begin by performing a soil test to assess the nutrient levels in your lawn. A soil test not only reveals the amounts of nitrogen, potassium, and phosphorus in your soil but can also help identify potential issues, such as pH imbalances. Once you understand what nutrients your lawn is lacking, you can apply the appropriate fertilizers and amendments to improve soil health. This will promote stronger grass growth and help reduce the likelihood of weed invasions in unhealthy turf.

With the necessary fertilizer NPK ratio in mind, use our fertilizer selector tool to find the ideal product for your lawn.

Step2 Follow Proper Lawn Care Practices

How to Aerate Your Lawn - Tips for Lawn Aeration

If your soil is difficult to work with, it may be necessary to reduce compaction and improve irrigation. Black Medic tends to thrive in areas where the soil is dry and compacted, often seen near sidewalks, driveways, curbs, and other areas where the soil is tightly packed.

Soil compaction limits root growth and reduces the movement of water, causing water to pool on the surface rather than being absorbed by the soil. This can hinder your grass and other plants from taking in the water and nutrients they need.

Aerating your lawn to alleviate compaction, ensuring proper drainage and irrigation, and maintaining healthy mowing practices will help keep your lawn vibrant and robust. A healthy lawn can outcompete Black Medic and other weeds.

Explore these resources for more tips on maintaining a healthy lawn throughout the year:

Grass Care Guides
Lawn Care Schedule for Cool-Season Grasses
Lawn Care Schedule for Warm-Season Grasses

Step3 Apply a Pre-Emergent Herbicide

How to Apply Pre-Emergent Herbicide in Split Applications

While good cultural practices can give your lawn a strong defense against weeds, applying pre-emergent herbicides (weed preventers) in both the spring and fall is a critical step to stop Black Medic from spreading.

Pre-emergent herbicides containing dithiopyr or isoxaben are particularly effective at preventing Black Medic growth.

When to Apply Pre-Emergents

Black Medic can act as both a summer and winter annual weed, germinating from seeds when soil temperatures warm in spring or cool in fall. To be effective, pre-emergent herbicides must be applied before the seeds germinate.

  • Spring Application: Apply pre-emergents after the soil thaws but before soil temperatures reach 55°F. This timing helps prevent other weed seeds from germinating.
  • Fall Application: Apply as soil temperatures cool to 70°F for effective control of winter-germinating seeds.

Split-Application Strategy

For better coverage and control, consider a split-application approach:

  • Apply the pre-emergent herbicide twice in the spring, spaced 6-8 weeks apart.
  • Repeat the process in the fall with two additional applications, also spaced 6-8 weeks apart.

Timing between applications can vary depending on the product used, so always refer to the product label for specific usage rates and detailed instructions.

Products we recommend for Step 3

We hope this guide has been helpful. If you’re still uncertain about identifying black medic weeds in your lawn, take a look at our guide on how to recognize black medic.

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