Black Medic is a very prolific seeder and as a member of the bean family can fix Nitrogen in the soil. This unwanted plant grows up quickly and produces those seeds early and often.

Pre Emergents may help some, thick mulches may help some, but getting the soil into a good healthy condition will do more. Black Medic commonly grows in compacted soils, soils lacking adequate amounts of organic matter. Take a good look at the soil these plants are growing in and correct what the soil problem is.

Here are the UMASS results of my rose garden's soil test:

Soil pH (1:1, H2O) 7.1

Macronutrients - ppm
Phosphorus (P) 201.2
Potassium (K) 626
Calcium (Ca) 4195
Magnesium (Mg) 448
Sulfur (S) 38.3

Micronutrients - ppm
Boron (B) 2.6
Manganese (Mn) 15.4
Zinc (Zn) 15.2
Copper (Cu) 1.3
Iron (Fe) 5.9
Aluminum (Al) 6
Lead (Pb) 0.0

Cation Exch. Capacity, meq/100g 26.2

Exch. Acidity, meq/100g 0.0

Calcium Base Saturation 80%
Magnesium Base Saturation 14%
Potassium Base Saturation 6%

Scoop Density, g/cc 0.94

Soil Organic Matter (LOI), % 6.9
Soluble Salts (1:2), dS/m 0.32
Nitrate-N (NO3-N), ppm 11

Comments:
Soil pH is too high for Acid-Loving trees and shrubs. (When pH is greater than 6.8, Cation Exchange Capacity (CEC) tends to be overestimated).

Soil test values for phosphorus and potassium are above optimum.

Only a source of nitrogen is necessary this year.

Phosphorus is excessive!!!

The lead level in this soil is LOW.

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WHAT DO I NEED TO DO TO IMPROVE THE SOIL?

WHAT CONDITION ENCOURAGES THE RECURRING BLACK MEDIC (MEDICAGO LUPINA)?

Here, in my west Michigan area, Black Medic grows best in compacted soils with low levels of organic matter that are somewhat more acidic then turf grasses like, below 6.0.

kimmq is kimmsr