Can You Grow Grass Under a Tree?

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Q. I just moved into a house with a beautiful old oak tree that shades a good portion of the lawn. I tried seeding, but not much happened. I'm worried that the soil is depleted or the root system of the tree is so near the surface that the grass can't establish itself. Do you have any suggestions?

---Lynn in Pittsburgh

I have a big old maple in my back yard. The tree takes everything out of the earth leaving rock hard soil, and in August I feel sorry for my grass. It's so sparse and the blades are so thin and weak, I can see them struggling for life. What can I do? I even tried sowing some seed that was supposedly indomitable from Canada, and it died. Help, please!

---Nancy in Emmaus, PA

A. Well, Nancy; if your "indomitable" seed was that worthless "Canada Green" I keep getting junk emails about, its no wonder it died. That's a blend of the absolute cheapest and least appropriate grasses I've ever seen. Avoid hype and stick with high-quality seed designed for your region, which for the two of you would be cool-season grasses.

And pretty much everybody's grass struggles in August in the Northeast! The cool-season grasses that predominate here come from very temperate areas of the globe—primarily the United Kingdom—and are tremendously stressed by the often-brutal heat of July and August.

And no grass is going to thrive if you sow it on rock-hard soil!

There are two big keys to grass seeding success. The first is to improve the soil with large amounts of organic matter in the form of compost (or well-aged mushroom soil, a resource widely available in your area thanks to the big mushroom growing regions nearby). The other is to sow at the correct time of year. The bluegrass, fescues and rye grass that thrive in the Northeast are cool-weather lovers. They establish beautifully when sown in the still-warm soils and cooling air of late summer/early Fall; struggle if sown in the cold soil of Spring; and just plain burn to a crisp when sown in Summer.

AND lawn care expert Dr. Nick Christians of Iowa State University (the researcher who pioneered the use of corn gluten meal as a natural weed and feed) warns that turf grass is essentially a sun-loving animal; even the most shade-tolerant types require about four hours of sun a day. If you don't get that much, and thinning of the tree's canopy won't help, he suggests you save your money and plant a shade tolerant ground cover like vinca or pachysandra instead.

If you think you can achieve that magic sunshine number, spread an inch of compost over the area in late summer, level it well, and sow the seed of a dedicated shade-tolerant grass. Fine fescue survives the best in deep shade, but does tend to look thin and wispy. Turf-type tall fescues will look more like a regular lawn—if you have enough sun to support them. Just be aware that all shade-tolerant grasses for the North are clumping types that need to be reseeded or over-seeded every couple of years; maybe EVERY year under a big ol' honking tree. That's no knock on them or you; it's just the way things are.

Long-term, have a very light hand with the fertilizer; plants in shade don't use nearly as much food as plants in sun. But be prepared to water as much as a lawn in full sun if the grass shows signs of drought stress thanks to those big honking tree roots sucking up all the moisture in the neighborhood. And cut high. Three inches tall after cutting is the drop-dead minimum (actually, the avoiding death minimum). Three and a half inches is better. Shorter than that and even four hours of sun can't provide enough energy for the root system.

The same basics apply to Southern lawns, except that the warm-season grasses that predominate down South are established in the Spring. Dr. Christians says that the best choice will be a named variety of St. Augustine specifically bred for shade tolerance. Bonus: St. Augustine IS a running grass, so once it's established it should stay filled in pretty much on its own. (Don't get your hopes up, Northerners; it won't survive our winters.)

One final note: As a walk in the woods will quickly reveal, plants don't typically grow right up to trees. Instead, these stately giants are surrounded by a kind of transition zone where greenery gives way to bare earth and the dramatic sculpture of the root flare. Go ahead and extend the lawn some towards the tree, but respect Nature and leave that 'frame' in place. Besides, you need a good foot open all around to allow for ease of mowing.

Q. My company is looking for a grass that can be grown under a 30 x 50 foot tent that's in place from May to October. We only host events there about once a week, but the tent has to stay up in between. We tried several seeding of supposedly shade-tolerant northern grasses, and unfortunately, grew more mushrooms than grass. Our brides prefer a lush lawn and mud-free weddings. We've considered laying sod, but have been told that even it might not survive a full season under a tent. Any idea what the odds are?

---"Event Planner" in Portland, ME

Oh yeah. Unless we're talking Astroturf, those odds are Zilch! Zero! Nada! Bupkiss! Minus 10 to the hundredth power! It's simply against the laws of Nature; I put a tent up in our backyard for a party once and the grass was dead in three weeks.

You have two options: One is to leave the actual structure in place, but arrange the material covering it so that the 'roof' can be pulled off and stored in between events. (This would also greatly prolong the life of the material.) The other is to lay some kind of portable floor inside. I remember an outdoor wedding where they laid wood parquet panels inside a tent for the dance floor and it was sensational.

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