The water has retreated. The basements have dried.
For many homeowners, the catastrophic flooding of September 2013 is becoming a distant memory. But chances are, your landscape hasn’t forgotten.
By Lisa Marshall
“When you get nearly a year’s worth of moisture in a week, there are bound to be lingering effects,” says Thad Johnson, owner of Longmont-based garden center Yatahai Gardens. “I’m already starting to see them.”
For those whose flower beds and garden plots survived, last fall’s heavy rain, unusually wet soil, potential exposure to flood-borne contaminants, and thick layers of silt and sand could pose unique challenges this spring, says Dr. James Self, Ph.D., director of the Soil, Water and Plant Testing Laboratory at Colorado State University in Fort Collins. And those who saw parts of their landscape wiped out have a unique opportunity to start fresh and create a more flood-resistant one.
Here’s a look at how things might be different in the wake of the flood, and what you might want to do as spring gets under way.
Walls of Weeds
Among the greatest beneficiaries of the 2013 flood were perennial weeds and grasses, including bindweed, brome, knapweed and foxtail barley. Typically, Johnson says, weed seeds drop in fall and lie idle on the ground—or are scattered far and wide via wind and birds—awaiting spring rains to help them germinate. Last fall’s torrential downpour enabled them to germinate early where they lay and get a head start on taking root.
By mid-January, the swaying golden strands of foxtail barley, a perennial grass that can be lethal to pets if the barbed seed heads lodge in their ears or digestive tracts, was already growing around Boulder County. Whatever unwanted grasses are on your property, you’ll likely have more of them this spring, and they’ll be firmly established. “The longer they have to take root, the harder they are to get out,” Johnson says. “That is going to be the big battle that people face this spring: weeds.”
His advice: “Put down that magazine and get to weeding.” And be sure to pull up grasses by the roots. The good news: Some annual weeds that would normally just be germinating, like amaranth and thistle, already bloomed and died last fall. So you won’t be pulling as many of them.
Rot or Not?
Some plants and trees accustomed to semiarid climes may have taken a beating from the rare autumn torrent, which was followed by a series of unusually wet snows. “The root-zone moisture level is definitely higher than normal,” Johnson notes. Aspen and pine trees, and perennials like columbine, heliopsis (oxeye sunflower) and gaillardia (blanket flower), are particularly susceptible to root rot and other diseases related to excess soil moisture. Browning needles, branch dieback, visible fungi, or wilted or yellowing leaves could be signs of root rot. When moisture-saturated ground freezes and thaws, it can also pitch perennials out of their beds, says Michael Morris, hard-goods manager at The Flower Bin in Longmont.
Both men advise surveying your landscape for diseased plants in early spring. You might save moderately affected plants by replanting them (after pruning off diseased roots) in well-drained soil mixed with compost. Using clean shears, prune a third of the top growth, which will give the roots a better chance to regrow. Be sure to disinfect pots and tools used on or around infected plants with a solution of 1-part bleach to 9-parts water.
There’s not much you can do to bring a seriously root-rotted plant or tree back to life, but if you’ve lost some, it’s better to replace them this spring than later in summer, when the heat will take its toll on new plantings.
In the weeks following the flood, gardeners were warned not to eat their vegetables if floodwaters had passed through them because they may have been exposed to contaminants from leach fields and septic tanks, or residues from mine tailings or household chemicals. By now, the winter chill has probably gotten rid of most of those nasty microorganisms, Self says.
But if you’re still concerned, you can kill them yourself by solarizing your garden soil. After normally prepping your garden—removing sticks and rocks and turning the soil—cover it with a large sheet of black plastic held down by bricks. “The sun will heat the black plastic and the soil underneath it up to 160 degrees to really sterilize the soil,” Self says. Stick a meat thermometer in the ground to check the temperature after three to four days. If it’s not quite hot enough, leave the plastic on longer. Solarization also kills a range of soil pests, including wilt and root-rot fungi, as well as noxious weed seeds.
If you live downstream from an old mine site, notice a foul smell or strange-colored oily residue in or near your garden, or are concerned about chemical residue in your garden, take a soil sample to the CSU Soil, Water and Plant Testing Laboratory and get it tested for $25. (For information, call 1-970-491-5061.) So far, Self says the lab has seen very little contamination as a result of the flood. “This isn’t something people need to be really concerned about.”
Of greater concern, Self says, is the amount of sediment or silt dumped on lawns and gardens by the rush of flowing floodwater.
“We’ve seen people with anywhere from a few inches to a few feet deposited on their property.” If you have only an inch or so on your lawn, you may be able to rake it out, add compost, peat moss or other organic material and work it into the ground with a core aerator, and then sprinkle grass seed on thin lawn areas.
If your lawn was buried in more than 2 to 3 inches of sediment, it may be time to reseed or re-sod. “Think of it as an opportunity to start over and do it right,” says Morris, noting that today’s grass seed is much more drought-tolerant and hardy than what was available five years ago. If your garden was covered in sediment or inundated with water, add more organic material this year than you have in the past, Morris says, to replace what was depleted.
This spring might also be a good time to think about better drainage for your property (see “Down the Drain” on page 86 for more information). Larry Elmore of Lyons-based Wild By Design landscape design firm recommends creating dry creek beds or swales seeded with native grasses to absorb excess water during heavy rains.
Strategically placed rocks and berms or a French drain (a perforated pipe running along a trench lined with crushed stone) also channel water from high spots on a property to places (like the garden) where you want more water.
“This event has been a great lesson in where water comes from,” Elmore says. “It’s an opportunity to take a good look at your property and see what can be done to mitigate future damage.”