Question
Hi James, My Mom and I need help.  We have a garden in the front of our home (purchased last year) and this year it developed a black tar like substance coating over the dirt.  Do you have any idea what this may be, and if so how do we get rid of it?

Thank you!

Answer
Hi Lori, I suspect it's algae.  Algae often grows on compacted soil and usually we find it's fairly acidic.  Check your pH.  For turf, flowers, most shrubs and vegetables, we want a pH of 6 to 6.5, for azaleas and hollies, closer to 5.5.
This area should be tilled to loosen the soil. I'd start collecting bagged leaves this fall and spread a couple of inches over the entire area.  Then I'd lime (if necessary) and till the area 4" - 5" deep.
Overseed the area with annual ryegrass this fall.  If the grass prospers, then till it under as a green manure next spring.
If it dies, then we look to some other cause.  Possibly drainage problems are causing the soil compaction, but the organic matter should prevent the soil from compacting again.
Let me know if this solves your problem.
Jim