What Is Top Soil?

    The term “top soil” is widely used, but what is top soil?  We sell 40 pound bags of spent mushroom compost at our store.  Some places sell decomposed bark mulch for top soil.  Either of these is good for amending soils low in organic matter (previously living material).  I would prefer the spent compost as opposed to the rotted bark.  But what is top soil?  It can be the soil that was taken from the top of the pile!

    I dug a hole 30 inches deep in my flowerbed.  My house is a split foyer built in the mid 70’s.  The upper 6 inches of my ground is excellent soil, further enhanced by my adding of amendments.  I found the next 6 inches to be hardpan clay – no big surprise to me since I had previously dug this far.  What astonished me was that the next 18 inches revealed the finest soil on the place.  The age of my flat lot would suggest that this was farmland prior to development.  The builder pushed aside the top soil and distributed the soil from the foundation over the lawn.  They then re-distributed the pushed aside soil over my lot.  Beneath all of this lies my native soil structure.  I do have good drainage in spite of the 6 inches of hardpan.  We should all have it so good in Fredericksburg!

    Good “top soil” should consist of equal particle counts of clay, silt, and sand.  Yes, I said clay!  Some clay is good – we simply have too much in Fredericksburg.  Additionally, the soil should contain between 2% and 5% organic matter.  The pH should range between 6 and 7.  If you are applying anything else, you may be adding to your pile of problems.

    Should you add top soil to your lawn?  Maybe.  One cubic yard of soil covers 324 square feet of ground at a depth of one inch.  A 10 yard dump truck of soil covers 3,240 square feet of ground at a one inch depth.  To add three inches of soil to a 10,000 square foot area requires approximately 10 dump truck loads of soil, assuming it meets the standards described in the previous paragraph.  Otherwise, you may be adding to your previously existing pile of concrete.  A former extension agent once said, “Adding top soil to your lawn is like pouring a cup of water into the Potomac River to raise the water level”.  His comments are very well put.

    Here are my closing points.  You should make sure you know what you are getting when you purchase “top soil”.  You should also make sure you are making a significant impact due for your efforts and expense.  Until next week.