# Do oak trees secrete an enzyme to poison my lawn? And can I neutralize it? **URL:** \ **Category:** Factual Questions\ **Created:** [June 4, 2012, 3:26pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038 "2012-06-04T15:26:43Z")\ **Posts on this page:** 18\ **Page:** 1
**Author:** ![Rhodes](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rhodes/32/273_2.png) [@Rhodes](https://boards.straightdope.com/u/Rhodes)\ **Post date:** [June 4, 2012, 3:26pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/1 "2012-06-04T15:26:43Z")
Most of the trees in my neighborhood appear to be [Southern Live Oak](http://en.wikipedia.org/wiki/Live_oak) or something very similar. The ones in my yard have 1.5" by 0.5" dark green leaves with no apparent lobes, and 0.6" by 0.4" acorns. For a few weeks in March or April, they produce a lot of smelly green pollen dust and debris, and then the year’s new leaves appear and the previous year’s leaves are shed. My grass is [St Augustine](http://en.wikipedia.org/wiki/St._Augustine_Grass), mixed with Bermuda grass where I have attempted to over-seed some bare areas. I have noticed several lawns in the neighborhood, including mine, have bare patches around the trees’ drip lines. The top half of each blade of grass turns yellow or brown, and then within a couple weeks the grass thins out until nothing is left except a web of runners. When I plant Bermuda grass seed in its palce, it usually sprouts nicely and then dies a couple months later. My hypothesis was that, in addition to the usual problems of drought, shade, and fungus, the trees are somehow poisoning the grass. Either thru the roots, or more likely via the rain dripping from the leaves. I searched Google and found nothing, so I figured the dead rings around so many trees was simply my confirmation bias. But then a few days ago my neighbor mentioned that the trees produce an enzyme to kill grass. His solution is to re-sod his lawn every 2 years. Is this enzyme real? Is there a product I can apply to neutralize it? Or am I just applying too much/too little water/fertilizer/sun/fungicide? ---
**Author:** ![VOW](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/vow/32/3043_2.png) [@VOW](https://boards.straightdope.com/u/VOW)\ **Post date:** [June 4, 2012, 3:33pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/2 "2012-06-04T15:33:32Z")
Many trees can affect the growth of plants around them. We had an enormous English walnut tree, and the only place for a garden was located partially under the tree. Nothing would grow beneath the drip line. A tree big enough to have a substantial drip line has perfected its survival tactics. My opinion is that it has something to do with the root system in the soil. The tree does NOT want competition. I wouldn’t even try to neutralize it. With the first rainfall or good soaking watering, whatever you would try to apply would wash away. And if your neutralizer DID work, you could very well end up with a dead tree. There’s probably a good reason why you see circular benches surrounding the trunks of older, established trees. ~VOW ---
**Author:** ![purplehorseshoe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/purplehorseshoe/32/2996_2.png) [@purplehorseshoe](https://boards.straightdope.com/u/purplehorseshoe)\ **Post date:** [June 4, 2012, 4:23pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/3 "2012-06-04T16:23:53Z")
Also, most oak trees have very dense canopies. Lawn grass needs full sun, so the tree simply out-competes the grass for UV light. In addition, their root systems can out-compete the grass from below, taking up the nutrients before the grass can utilize it. ---
**Author:** ![Hello\_Again](https://avatars.discourse-cdn.com/v4/letter/h/85e7bf/32.png) [@Hello\_Again](https://boards.straightdope.com/u/Hello_Again)\ **Post date:** [June 4, 2012, 4:45pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/4 "2012-06-04T16:45:32Z")
Kansas State University says “[What kills the grass under oak trees is the dense shade and the trees’ highly competitive roots.](http://www.ksre.ksu.edu/news/story/acorns_oaks112211.aspx)” It also notes that Kansas soils, which are very alkaline, are not significantly affected by the tannins from oak leaves. To me this leaves (heh) open the possibility that soils which are less alkaline, could be affected. On that front, short of waving a magic wand so that rain no longer drips off fall leaves, I doubt there’s anything you can do about it. In theory you could lime the soil but, see above, the grass won’t grow anyway. ---
**Author:** ![newme](https://avatars.discourse-cdn.com/v4/letter/n/e0b2c6/32.png) [@newme](https://boards.straightdope.com/u/newme)\ **Post date:** [June 4, 2012, 10:25pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/5 "2012-06-04T22:25:56Z")
Oaks will inhibit the growth of other plants in what is called allelopathy. > **[Lady Bird Johnson Wildflower Center - The University of Texas at Austin](https://www.wildflower.org/expert/show.php?id=8072)** > [@](#): > > Sod is greatly overdone, especially under oaks. Oaks, including live oaks, are allelopathic, which means they exude substances to inhibit growth of other plants competing for light, water and air beneath them. Along with that, there is the shade that such a large tree casts over the grass. So, the grass is doomed in two ways. ---
**Author:** ![Rhythmdvl](https://avatars.discourse-cdn.com/v4/letter/r/85f322/32.png) [@Rhythmdvl](https://boards.straightdope.com/u/Rhythmdvl)\ **Post date:** [June 4, 2012, 10:41pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/6 "2012-06-04T22:41:00Z")
There is unrest in the forest; there is trouble with the trees. For the maples want more sunlight, and the oaks ignore their pleas. ---
**Author:** ![Qadgop\_the\_Mercotan](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/qadgop_the_mercotan/32/83_2.png) [@Qadgop\_the\_Mercotan](https://boards.straightdope.com/u/Qadgop_the_Mercotan)\ **Post date:** [June 4, 2012, 10:45pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/7 "2012-06-04T22:45:03Z")
The best tool for neutralizing hostile tree activity is a chain saw. ---
**Author:** ![Zakalwe](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/zakalwe/32/270_2.png) [@Zakalwe](https://boards.straightdope.com/u/Zakalwe)\ **Post date:** [June 5, 2012, 12:14am UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/8 "2012-06-05T00:14:22Z")
> [@Qadgop\_the\_Mercotan](#): > > The best tool for neutralizing hostile tree activity is a chain saw. I know you’re kidding, but in some areas of the South (including mine) you actually have to get a permit(s) before cutting down a Live Oak with a diameter of more than (IIRC) 2 ft - which is pretty damn small as Live Oaks go. ---
**Author:** ![jnglmassiv](https://avatars.discourse-cdn.com/v4/letter/j/f07891/32.png) [@jnglmassiv](https://boards.straightdope.com/u/jnglmassiv)\ **Post date:** [June 5, 2012, 12:20am UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/9 "2012-06-05T00:20:36Z")
> [@newme](#): > > Oaks will inhibit the growth of other plants in what is called allelopathy. I’d never heard this term. The wikipedia suggests that true allelopathy is less common than reported. > **[Allelopathy](https://en.wikipedia.org/wiki/Allelopathy)** > > Allelopathy is a biological phenomenon by which an organism produces one or more biochemicals that influence the germination, growth, survival, and reproduction of other organisms. These biochemicals are known as allelochemicals and can have beneficial (positive allelopathy) or detrimental (negative allelopathy) effects on the target organisms and the community. Allelopathy is often used narrowly to describe chemically-mediated competition between plants; however, it is sometimes defined more bro... ---
**Author:** ![excavating\_for\_a\_mind](https://avatars.discourse-cdn.com/v4/letter/e/e8c25b/32.png) [@excavating\_for\_a\_mind](https://boards.straightdope.com/u/excavating_for_a_mind)\ **Post date:** [June 5, 2012, 1:44am UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/10 "2012-06-05T01:44:10Z")
Perhaps a Water Oak? Very similar tree. Both variates will take in a lot of water. You can get the grass to grow under them, however. They do it on golf courses, so you can do it in your yard. It takes a lot of water, though. It helps to put a boarder around your tree and fill it with mulch (I’m sure you’ve seen this). This helps prevent the tree from competing with the nearby grass. St. Augustine does well if it gets a lot of water and it is hot, which is why it does well in Texas. It is rather drought resistant, if it gets water once a week or two, and it is well established, it will survive where the Bermuda will just go dormant. The St. Augustine will respond well to frequent watering and hot weather, so in Texas, you can grow a very dense lawn in the spring and keep it through the summer with minimal watering. It takes a good growth in the spring, however. excavating (for a mind) ---
**Author:** ![BwanaBob](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/bwanabob/32/2985_2.png) [@BwanaBob](https://boards.straightdope.com/u/BwanaBob)\ **Post date:** [June 5, 2012, 12:57pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/11 "2012-06-05T12:57:03Z")
> [@Rhythmdvl](#): > > There is unrest in the forest; > there is trouble with the trees. > For the maples want more sunlight, > and the oaks ignore their pleas. Nice Rush reference +1. ---
**Author:** ![naita](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/naita/32/5862_2.png) [@naita](https://boards.straightdope.com/u/naita)\ **Post date:** [June 5, 2012, 1:19pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/12 "2012-06-05T13:19:58Z")
> [@excavating\_for\_a\_mind](#): > > It helps to put a boarder around your tree and fill it with mulch (I’m sure you’ve seen this). This helps prevent the tree from competing with the nearby grass. a) I question the legality of this. and b) Does it have to be a boarder? Could I use a vagrant or an unloved family member instead? Or a skier? ---
**Author:** ![njtt](https://avatars.discourse-cdn.com/v4/letter/n/ecd19e/32.png) [@njtt](https://boards.straightdope.com/u/njtt)\ **Post date:** [June 5, 2012, 1:38pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/13 "2012-06-05T13:38:43Z")
Whatever it is (if it is anything), it ain’t an [enzyme](http://en.wikipedia.org/wiki/Enzyme). ---
**Author:** ![Jackmannii](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/jackmannii/32/311_2.png) [@Jackmannii](https://boards.straightdope.com/u/Jackmannii)\ **Post date:** [June 5, 2012, 2:09pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/14 "2012-06-05T14:09:06Z")
I would much rather have healthy live oaks (which are amazing trees, though not very well suited to small properties) than St. Augustine, which is a poor excuse for a grass. A good shade tree is far more important in a hot climate. Instead of grass under/around a live oak, there may well be a good ground cover alternative. The local/state hort department/extension service should have recommendations. When I lived in Texas, an excellent source was Sally Wasowski’s “Native Texas Plants”. ---
**Author:** ![Rhodes](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rhodes/32/273_2.png) [@Rhodes](https://boards.straightdope.com/u/Rhodes)\ **Post date:** [June 5, 2012, 2:38pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/15 "2012-06-05T14:38:10Z")
> [@Qadgop\_the\_Mercotan](#): > > The best tool for neutralizing hostile tree activity is a chain saw. > [@Zakalwe](#): > > I know you’re kidding, but in some areas of the South (including mine) you actually have to get a permit(s) before cutting down a Live Oak with a diameter of more than (IIRC) 2 ft - which is pretty damn small as Live Oaks go. The one in the middle of my front yard has about a 2 ft trunk and maybe a 40 ft diameter canopy. A smaller one in the corner of the front yard mingles branches with the big one and extends out over the street, and apparently causes a dead stripe across the neighbor’s parking strip. But he gets his vengeance - a bigger one in his back yard ensures that nothing grows between my house and side fence. I trimmed the branches that were scraping my chimney, and a few days later he cut those branches off completely. When I cut off a big horizontal branch, and when a guy climbed up the tree to trim a bunch of smaller branches, my front yard was noticebaly sunnier but not noticeably greener. The city wants to fix some sidewalks, and they are going to make me pay for the City Forester to determine whether the trees will damage the new sidewalk. If so, he will either cut down the trees or install a root barrier at my expense. ---
**Author:** ![Really\_Not\_All\_That\_Bright](https://avatars.discourse-cdn.com/v4/letter/r/e8c25b/32.png) [@Really\_Not\_All\_That\_Bright](https://boards.straightdope.com/u/Really_Not_All_That_Bright)\ **Post date:** [June 5, 2012, 2:48pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/16 "2012-06-05T14:48:08Z")
I had always wondered why the hell we couldn’t get grass to grow around the 4-foot diameter oak in our front yard. I hate the bloody thing already, but the wife and realtor think it’s good for the value of the house (and we’d have to petition the HOA before cutting it down, anyway). ---
**Author:** ![Rhodes](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/rhodes/32/273_2.png) [@Rhodes](https://boards.straightdope.com/u/Rhodes)\ **Post date:** [June 5, 2012, 2:48pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/17 "2012-06-05T14:48:28Z")
> [@excavating\_for\_a\_mind](#): > > Perhaps a Water Oak? Very similar tree. Nope. The leaves look like [this](http://www.floridasnature.com/images/Southern%20Live%20Oak%20(Quercus%20virginiana)_1.jpg). > [@](#): > > Both variates will take in a lot of water. You can get the grass to grow under them, however. They do it on golf courses, so you can do it in your yard. It takes a lot of water, though. It helps to put a boarder around your tree and fill it with mulch (I’m sure you’ve seen this). This helps prevent the tree from competing with the nearby grass. > > St. Augustine does well if it gets a lot of water and it is hot, which is why it does well in Texas. It is rather drought resistant, if it gets water once a week or two, and it is well established, it will survive where the Bermuda will just go dormant. The St. Augustine will respond well to frequent watering and hot weather, so in Texas, you can grow a very dense lawn in the spring and keep it through the summer with minimal watering. It takes a good growth in the spring, however. I put in an 8-ft diameter border. I’m thinking of extending it several more feet. But my yard isn’t very big. The tree reaches the driveway, the house, the fence, and the street. So extending the border to the drip line would mean getting rid of my lawn completely. That may be an option someday, but not while my kids are young and need a place to paly. ---
**Author:** ![VOW](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/vow/32/3043_2.png) [@VOW](https://boards.straightdope.com/u/VOW)\ **Post date:** [June 5, 2012, 3:38pm UTC](https://boards.straightdope.com/t/do-oak-trees-secrete-an-enzyme-to-poison-my-lawn-and-can-i-neutralize-it/624038/18 "2012-06-05T15:38:12Z")
> [@naita](#): > > b) Does it have to be a boarder? Could I use a vagrant or an unloved family member instead? Or a skier? Be selective in choosing your skier. Some do not go AROUND trees very well! ~VOW