Black Medic

An Annual Summer Weed with a Yellow Flower that Dies in the Cold Weather

Weed Black Medic Flower

What Is Black Medic?

Black Medic, also known as Medicago lupulina or Yellow Trefoil, is a Summer annual weed. This means that it germinates sometime in the late Spring, grows well during the heat of Summer, then dies off with the cold weather. Black Medic is sometimes referred to as Yellow Clover because it looks like Clover with teardrop-shaped leaves, but has a yellow flower. The seed pods of Black Medic are also unique. They turn black when they're ready to drop. If you can remove the Black Medic before this happens, it will help eradicate the plant, as the seeds are its only way of reproducing and they can stay viable for years and throughout Winter. 

What Causes Black Medic?

It's important to understand the conditions needed for Black Medic to thrive. A little Black Medic is normal. It will fill in the bare areas during the heat of Summer. A lot of Black Medic however, typically indicates that your lawn is being mowed too short in the Spring and Summer, your grass types are not strong or healthy enough to compete with the weed or your soil is compacted. If you notice the Black Medic growing by the roadside or next to a sidewalk, this is a sign that your soil quality is compromised due to foot traffic and compaction is the underlying problem.

How To Get Rid Of Black Medic?

Since Black Medic has a short lifespan, the bulk of your effort should go towards improving your lawn to prevent this weed from populating the following year. But there are a few things you can do to eliminate the weed right away.

  1. Pick the Black Medic. If you're able to do this when the soil is wet, that would be ideal, as the roots will more easily and cleanly pull out of the ground. Black Medic grows out of a central location, so hand weeding can be very effective for removing the weed from large areas. 
  2. Another option for elimination is to use a natural weed suppressant, such as Weed Beater Fe, which will be successful in killing the weed, however it also causes stress on the surrounding grasses, so use it sparingly.

How To Prevent Black Medic?

Black Medic and other annual weeds will emerge where your lawn is not competing. It could be that you’re mowing your lawn too short, which is keeping your grasses from growing stronger than your weeds. It could also be that the grasses you have are too weak and old and just don’t fight that well. Another option is that you have dry, compacted soil. Luckily, there are several ways to address the issues that could be resulting in the Black Medic in your lawn.

Mowing Problems

  1. One of the worst things you can do for your lawn is remove too much of the grass blade in a single mowing. Removing more than 1/3 of the grass blade length in a single mowing will turn the grass brown, stop root growth, and invite in weeds. So set your mower blades high.
  2. Dull mower blades are another common mowing issue because they rip the grass, instead of cutting it. This leaves your lawn vulnerable to disease and weeds and also dehydrates the grass blades, causing them to turn brown. A hardware store should be able to sharpen your blades for you. Try to do this every 20 hours worth of cutting or at least once per season

Grass Problems

  1. If you have older poor grasses, a total Lawn Renovation might be the best choice.
  2. If you don’t want to go that far, simply Slice Seeding your current lawn should make a big difference.

Soil Problems

  1. Given that compacted soil is an ideal environment for Black Medic to grow, we recommend aerating your soil. You can do Core Aeration or Liquid Aeration. If you'd like a DIY solution for aeration, try Liquid Aerator on the areas where you're noticing the problem.
  2. Lastly you can try our Organic Soil Builder application, which will add valuable organic matter and nutrients to your soil, serving as an organic fertilizer that will promote healthy and balanced grass growth. 

Contact us to learn more or to get our opinion on what would be best for your specific situation.

How To Identify Black Medic In Your Lawn

Weed Black Medic Identify
  • Bright yellow flower in late Summer
  • Tear-drop shaped leaves
  • Low-growing, crawling weed
  • Leaves grow in groups of three
  • Often found by roadsides & sidewalks

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