If you have found this article, you have either experienced having some grass grow through your above ground swimming pool’s liner, or you are planning on getting an above ground pool and heard that grass can grow in it.
To verify this, grass can grow through a pool liner. For 35 years, I have seen it and learned how to prevent it from happening.
With the exception of a concrete floor, there is no guarantee that nutgrass or nutsedge won’t grow through an above ground pool liner. You can greatly lessen the chance of it growing by removing all of the sod’s root mass, using a granular nutgrass killer, and then installing a liner guard just before installing the pool’s liner.
NOT ALL TYPES OF GRASS CAN GROW THROUGH A POOL LINER. ONLY NUTGRASS
It’s common for people to think that anything can grow through a liner. This is not true, but there is one type of grass that will absolutely grow through your pool liner just like it’s not even there. And that is nutgrass or nutsedge. Out of the few naturally occurring things that can make a hole in a liner, nutgrass is the most common.
Plants need sunlight to grow. This is why nothing grows through pool liners and how weed blocks work. Even if you put a pool up directly on the grass, the grass will die because it cannot get any sunlight through the liner.
Nutgrass is a different story. Nutgrass can lie dormant and then decide to grow straight up forming a needle-like blade. This needle blade will poke through most things and easily pierce a vinyl liner on the way to finding sunlight.
NUTGRASS CAN GROW THROUGH BLACK ASPHALT
Over the decades of me working with above ground swimming pools, I’ve come across some non-believers about just how able nutgrass is at growing through things. They believe that a simple week barrier or plastic sheeting(visqueen) will do the trick and that I’m just trying to sell them something.
“Have you ever seen grass growing through black asphalt on the side of a road or in a parking lot?”, I always ask. “Well, that’s nutgrass. And if it can grow through asphalt, what do you think a little layer of plastic can do to stop it”? If they have ever noticed grass growing through a blacktop, then they get it and take my advice after that.
YOUR YARD MAY NOT HAVE NUTGRASS, BUT IT’S HARD TO TELL IF YOU HAVE IT
Usually, when the subject of nutgrass comes up, I get two reactions. The first is the guy who says “I don’t have to worry about that. My yard doesn’t have nutgrass”. Now, I’m a big believer in the power of positive thinking, but having a high level of surety about not having nutgrass in your yard won’t keep you from having it.
The second response I get is the question “How do I know if I have nutgrass”?
My answer is always “You don’t”. There are two things about nutgrass that make it hard to tell if it’s there. One is that it looks like normal grass and blends in well with different types of grasses. The other is that it can be lying dormant, and if so, there will be no sign of it except the little round nut it has attached to it.
Sometimes I can find and see nutgrass while digging for the pool installation. Other times I can clearly see it when someone removes the grass prior to me getting there for the install and some blades of it have grown up in the open cleared area of the yard.
The only way that I know how to identify it is by gently digging up a single green blade of grass and finding that it has a small round brown nut attached to it by a sturdy string-like root. That’s it.
There is no other way for me to identify it, so I can never say that a yard definitely doesn’t have it. It can occasionally flower, and when it does, you may be able to identify it. I wouldn’t rely on that though unless you are someone who works with grasses and has an eye for it. And if you are one of those people, then you know more than I about it.
SOME AREAS OF THE COUNTRY DON’T HAVE NUTGRASS
When I started installing above ground swimming pools in the eighties, the understanding was that nutgrass only grew in the southeast US states. Over the decades though, nutgrass migrated north and now grows in almost all areas of the US.
USING A LINER PAD OR LINER GUARD WILL NOT GUARANTEE PREVENTING NUTGRASS FROM GROWING THROUGH A POOL LINER
When liner pads first came out, retailers and manufacturers were giving guarantees that using a liner pad will stop nutgrass from growing through a pool liner. They found out quickly that wasn’t true, so they stopped.
Occasionally, I’ll come across a retailer who will say a liner pad prevents nutgrass damage. If you see this, it will tell you one or two things about the retailer. They either don’t know what they are talking about or don’t care and are trying to sell you something no matter what. Either one should give you pause in buying from them.
3 THINGS I RECOMMEND TO HELP PREVENT NUTGRASS FROM GROWING THROUGH YOUR ABOVE GROUND SWIMMING POOL’S LINER
As I stated earlier, only a concrete floor will guarantee no nutgrass damage to 100 percent. Concrete is expensive though and not really worth the hassle and expense for almost everyone getting an above ground pool.
There are some things you can do though that work really, really well at preventing nutgrass from growing under your pool.
1 When preparing the ground for installation, remove all of the root mass associated with the grass
Even with the less expensive Intex/Coleman soft-sided above grounds, all the grass should be removed before installing on the earth. Probably the most common mistake people make with installing soft-sided pools is that they don’t remove the grass and just try to level the earth by adding sand over the grass.
You want to remove all the grass AND all the root mass (sod) along with it before leveling and installing the pool.
Many years ago, I only had a sod cutter to remove the sod for my above ground pool installations. And even though sod cutters work very well, I eventually graduated to using a small skid-steer (Bobcat type) machine. A sod cutter is adjustable and can remove up to four inches deep of sod. This is usually deep enough to get most of the root mass associated with the grass.
When I stopped using a sod cutter and replaced it with a skid-steer machine, I started taking out more than the four inches of sod mass that a sod cutter could remove. This has a minor negative in that there is more earth to deal with as I am taking out more, and the pool will sit in the ground a little lower. But I noticed something after a while of doing this.
I noticed that since I had been using my machine to remove the sod, there were much fewer occurrences of nutgrass growing in the pools I installed. I eventually deduced that this was because I was taking out more of the root mass (more than 4” deep) of the sod.
Most if not all of the nutgrass is in the sod. Removing all of it will greatly reduce the chance of having nutgrass grow through your future pool.
2 Purchase and properly apply a granular nutgrass killer
As a pool installer, I buy 50-pound bags of the granular chemical that kills nutgrass. A couple of times over recent years, I have run out of killer and was forced to go to a Home Depot or Lowes to get whatever they carry that kills nutgrass.
What these stores carry is this liquid nutgrass killer made by Image. Now, I’m not saying that this product is not good. What I am saying though is that I have applied this liquid product and it didn’t do a good job at preventing nutgrass from growing through pool liners.
Since nutgrass can lie dormant for a while, it’s best to use the granular type of killer for preventing it with pool liners. This is because the chemical is a “preemergent”, which means it is designed to kill the plant right when it starts to grow.
Applying enough granular nutgrass killer with a spreader will evenly distribute the chemical over the entire pool bottom. You’ll want to apply this directly to the earth before the liner and/or liner guard goes down so it can make a nice top layer of poison.
NOTE: I have seen instructions that say to rake and work this nutgrass killer into the earth. I strongly disagree with this instruction. I instead believe that an even layer of the preemergent is best at preventing nutgrass from growing through a pool liner.
3 Purchase and lay down a liner guard/pad
By themselves(without nutgrass killer), a liner guard or pad will only marginally prevent some nutgrass from making it through the pool’s liner on it’s way to sunlight.
But if you use one in addition to having a good layer of nutgrass killer just beneath it, then it works pretty well. My feeling is that the liner pad helps create a better “death zone” for the chemical killer to work. The nutgrass only has so much time and energy to make it through to sunlight. If it takes too long to get to the sun (penetrating the liner), then it will die.
Doing all three of the above things will greatly reduce the chance of nutgrass growing through your pool liner. One or two of these things will help a lot, but doing all three is magic.
IF INSTALLING THE POOL TWO FEET IN THE GROUND, YOU DON’T HAVE TO WORRY ABOUT NUTGRASS
Here in Central Florida, I have seen nutgrass as far as eighteen inches in the ground. This is super rare and typically going down even one foot will remove any nutgrass in the earth.
Many semi-inground installs will go down about half the height of the pool or 2-2.5ft. If you are doing this, don’t worry about nutgrass. It doesn’t exist that far in the earth.
A LIST OF THINGS THAT WILL NOT PREVENT NUGRASS FROM GROWING THROUGH AN ABOVE GROUND SWIMMING POOL LINER
If you read above, then you know that nothing is a guarantee for preventing nutgrass from growing through a liner except concrete. But some people just don’t hear this. After me telling them that, they still ask “OK but what about this or that”? Here then is a list of materials that people ask me about anyway that DO NOT necessarily prevent nutgrass from poking through the pool’s liner.
1 A two, three, or four-inch layer of mason or sugar sand
2 A liner guard/pad
3 Liquid nutgrass killer
4 Expensive foam boards(that are taped together to make a pool bottom)
5 A gallon of Round-up
7 Weed block
8 Hard base material – Some will think they need to add a hard material as a base so their pool won’t settle. This is not only unnecessary to prevent settling, it also won’t prevent nutgrass from grow up and through your liner.
A FINAL WORD ABOUT NUTGRASS IN ABOVE GROUND POOLS
Typically, nutgrass isn’t an issue. Most will put down a nutgrass killer or a pad and it will help a little if this persistent weed is in their yard. If you get a blade or two that grows through the liner, it surely sucks but is really not a big deal and easy to fix.
Some yards will have a lot of nutgrass though. I have seen pools with hundreds of blades growing through the liner and it looks like a rice field. That is not good.
If, while you are installing your above ground pool (or having it installed), you identify nutgrass in the ground, make sure and take the above extra steps. Whenever I see nutgrass before my install, I will at least apply double the granular chemical I use to kill it. That chemical is expensive, but it’s worth not having the pool get a bunch of blades of grass grow through the liner a few days later.