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Published May 31, 2009, 12:00 AM

Turf wars: Horticulturists share tips on how to best heal your yard from effects of flooding

When Pam and Wayne Anderson host a high school graduation party for their daughter, Murphy, on Saturday, their River Drive home in Fargo will be clean and company-ready.

By: Tammy Swift, INFORUM

When Pam and Wayne Anderson host a high school graduation party for their daughter, Murphy, on Saturday, their River Drive home in Fargo will be clean and company-ready.

Their flood-ravaged yard, however, will be another story. The backyard still bears the wide, naked band of earth where a 10-foot-tall wall of sandbags stood. In a side yard, whole sandbags were sucked into the quicksand-like stew of wet river clay. And in the front lawn, the sidewalk and much of the green turf have been reduced to mud – evidence of the heavy-equipment routes used to haul load after load of sandbags.

“I’ve got some plants in pots, and that’s as good as it’s going to get,” Pam Anderson says with a laugh.

After all, she figures her friends and neighbors will understand. This year, sandbagging, dikes, flooding and heavy equipment have wreaked havoc on even the plushest and proudest of lawns.

Fortunately, lawn rangers need not despair. Todd Weinmann, horticulturist with the North Dakota State University Extension Service, and Randy Nelson, horticulturist with the University of Minnesota Extension Service, recently presented a class on repairing flood-damaged lawns.

And for those who were too busy dumping sandbags or cleaning out basements to attend, here is a list of the most important things to know – which should also solve problems in lawns not affected by flooding:

In a deep rut

Major damage caused by heavy equipment on wet soil is extremely common. An exhausted homeowner may be tempted to fill the ruts with leftover sand and cover the whole mess with sod. “That would be a disaster,” Weinmann says.

Adding any sand to our clay soils will only produce a hard, bricklike substance that’s more like gravel than garden soil.

“You would think the sand would lighten it up,” Nelson says. “But it does just the opposite. It makes it very hard. Just avoid sand.”

The best solution takes more time upfront but produces much better results:

  • Call before tilling: Remember to call local utilities first in case there are any important wires or cables in your backyard. In the yard in the photo at left, Nelson says, they found 1 foot of exposed telephone or cable line sticking out of one of the ruts.
  • Remove all debris: That includes garbage, sandbags, rocks, pea gravel and anything else that makes the soil less friable.
  • Disk or till the soil: Nelson recommends working to a depth of 4 to 6 inches – the same depth of most cool-weather grasses’ root systems.
  • If needed, add additional soil: matching it to the texture and weight of your existing soil. If adding soil, Nelson recommends splitting it and adding it half at a time. So, if adding 6 inches of new soil: Put 3 inches of new soil on; till that into your existing soil; then top with the next 3 inches of new soil. Rake until level.
  • Pump up the soil with a starter fertilizer: Feed fledgling grasses with a higher rate of phosphorous vs. nitrogen or potassium (the ratio should read 10/20/10 or 10/20/15 on the container). Apply at a rate of ½-pound of nitrogen per 1,000 square feet. The phosphorous will help boost the young grass plant’s growth and help it spread faster.
  • Reseed or re-sod? The choice is up to you. If you do sod, choose a mineral vs. peat-based sod, Weinmann says. “Because of the type of soil we have, this will save you a lot of headache and expense down the road.”

If you decide to reseed, the right mix is essential, Nelson says. If your lawn is:

  • Low maintenance/sunny (meaning you fertilize only once a year, don’t plan to water it  weekly, and might get behind on mowing once in awhile): Choose a mix that’s 50  to 60 percent Kentucky Blue Grass, 30 to 40 percent fine fescue and no more than 10 percent of perennial rye grass (some people don’t like how the rye grasses look, and they can be less winter-hardy).
  • Low maintenance/shady: Choose a mix that’s 50 to 60 percent fine fescue, 30 to 40 percent Kentucky Blue Grass with increased shade tolerance, and 10 percent or less perennial rye grass.
  • High maintenance/sunny (meaning you fertilize several times a summer, never mow the grass too low and water it four to five times during rain-free weeks): Choose a blend of Kentucky Blue Grasses. These can be hard to find, but some local nurseries will actually mix this blend for you. Look for Kentucky Blue Grasses that are labeled “improved.” They require more nitrogen but can also handle lower mowing heights.

Homeowners are often concerned whether the reseeded portions will match their existing lawns. As a general rule of thumb, go with the improved varieties of Kentucky Blue Grass for any lawns planted less than 15 years ago and for any sod.

A little healthy pressure

After seeding – especially if you tilled first – it’s a good idea to firm up the soil again. This will “snug up” the soil around the seeds, making it easier for them to germinate, Weinmann says.

To do this, use a lawn roller (available at hardware or home/garden stores) and fill it halfway with water. Run it over the planted area several times. “You don’t want to compact it like concrete,” Nelson says. “But just firm it up so that when you step on it, your foot will make an imprint and not a deep hole.”

Less-drastic measures

Some lawns have flood-related damage, if not to the extent that the Andersons’ house did. They may have shallow ruts, heavily driven paths or bald spots. For these situations, Nelson and Weinmann suggest:

  • Rent a core aerator from a rental shop. This will punch dozens of 2-inch-deep holes in the thatch, the layer of “woody” organic matter that develops between the soil surface and the growing vegetation. If thatch gets too thick, it can trigger insect and disease problems. Aeration also keeps the soil from growing too compacted and helps the lawn retain more nutrients and water.
  • When to use the aerator will depend on how much soil you’re adding. If you only need to add a ½-inch or less, you can do the aeration after adding the soil. But if you need to add quite a bit of soil, do the aeration first before adding soil.
  • Be vigilant for leftover clay. Lots of clay and sand have been left behind from our flood-fighting efforts. Remember that nothing will grow on subsoils, so top any clay with 4 to 6 inches of good topsoil if you plan to plant anything there, Weinmann says.
  • Help grass seed along. It’s not enough to simply sprinkle grass seed on dead spots and then pray that it grows. Scrape away the dead grass and work in the grass seed about ¼ of an inch so it can germinate. Water vigilantly and stake off area to prevent traffic.

In 20 days or so, you should start seeing the first few hopeful blades of green, Weinmann says.

For more information on lawn-related questions, contact NDSU Extension horticulturist Todd Weinmann at (701) 241-5707 or U of M Extension horticulturist Randy Nelson at (218) 299-5020.

Readers can reach Forum reporter Tammy Swift at (701) 241-5525 or