The Lawn Coach: Pond Slop

The Lawn Coach
Pond Slop

Q: Dear C.J., Is pond soil supposed to be good for use a s topsoil? The previous homeowners apparently used pond soil and my lawn does not drain very well at all. The surrounding neighbors all have very sandy soil and they don't seem to have this problem. Any advice?
A: Yes, I do have some advice. Call up the previous owners and politely ask them what on this green earth they were thinking when they laid that slop on top of your property. Of course, they may not answer so politely, so allow me to expound upon your issue and direct you in a more constructive approach.
The soil at the bottom of ponds can have a whole host of problems that do not make it ideal for a home lawn situation. Aside from fish poop (my 7 year old son dared me to work the word "poop" into a column. Now he has to let me beat him in a video game just once), there's problems with iron, clay, and anaerobic bacteria (my 9 year old dared me to work the word "anaerobic" into a column. He's just strange). But at the basics, ponds exist because the soil at the bottom does not drain. Why someone would get the bright idea that this impermeable (my wife dared....oh forget it) muck might create a good lawn growing medium is beyond me, but I've heard of this issue before.
Given that the neighborhood seems to be a sandy one, I'm going to conveniently jump to the conclusion that the pond slop was spread on top of sand. That would bolster your description on non-drainage nicely. Whenever you lay a finer textured soil (like the scientifically named "slop") on top of a coarser textured soil like sand, you create what is known as the "Sponge Effect."
Take a sponge and get it nice and wet. Now lay it on top of a cooling rack so it is essentially suspended in air. What happens? The sponge holds onto the water pretty well. In fact, most of the water will eventually leave the sponge through evaporation, not drainage. The pond soil on top of=2 0the sand acts in exactly the same way. Now, make a stack of five or six wet sponges. Aside from garnering strange stares from the rest of the family, what happens now? The top several sponges will drain down into the lower ones, at which point the lower ones become over-saturated and drain out onto the counter and drip down the front of the cabinets onto your shoes. This is the ideal drainage you want to have in your lawn, and it results from having a nice deep, uniformly textured soil layer.
So, what to do? The first option is to just have the lousy stuff scraped off and carted away. Since I don't know the dimensions of your yard, I don't know just how feasible this option truly is. It may end up being pretty costly. The other, less expensive option would be to simply roto-till the pond "soil" into the underlying sand. This way, you won't have that defined layer difference that is the root of your drainage problems. Instead, you'll have a more uniformly mixed up blend of 1/2 pond soil and 1/2 sand. The water really shouldn't have a problem draining through that. Once you've fixed the layering problem, you can either re-seed or sod to get a new lawn in place.
Thanks for writing in! And Dad, if you are reading this...antidisestablishmentarianism. You owe me a beer.

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