Growing past the flood

Unity of Boulder\'s flood saturated Sustainable Living Project garden
Courtesy of Tom West

What we’ve learned about growing food in a post-flood world

Though more than six months have passed since the September flood that destroyed homes, displaced roads and scarred landscapes, remnants of the flood still mark the land of Boulder County in the form of erosion and sediment deposits. Farms, gardens and backyards with flood damage may need to be assessed or even tested for growers to determine what needs to be done to their property to restore its condition for another growing season.

Boyd Byelich, district conservationist of Boulder County for the U.S. Department of Agriculture Natural Resources Conservation Service, estimates that 40 to 50 of Boulder County’s 600 farmers — from two-acre vegetable farms to 1,200-acre sugar beet and corn farms — were directly effected by the flood. According to Ron Carleton, deputy commissioner of agriculture for Colorado’s Department of Agriculture, the biggest concerns for farmers and other county residents with flooddamaged land are erosion and the deposit of silt.

Farms of all sizes, and local growers too, can take advantage of Colorado State University Extension’s soil lab tests to aid in their efforts in correcting the damage to their land. CSU Extension’s soil testing includes a particle-size analysis to determine the soil texture. According to a document by Texas A & M professors titled Soil Testing Following Flooding, Overland Flow of Wastewater and Other Freshwater Disasters, if soil has too much of a clay consistency, water will not evaporate, depriving the saturated ground of the oxygen it needs to enable plant germination and growth.

According to the document, “When sandy materials are deposited on top of finer textured soils [clay loams and clays], the abrupt change in soil texture [defined as the percent sand, percent silt and percent clay] can substantially reduce subsoil water infiltration. Deep tillage usually corrects this problem if the deposit is less than eight inches deep.”

James Self, director of CSU Extension’s Soil, Water and Plant Testing Lab, stresses the need to even out the deposited silt by mixing it with the remaining soil below, as well as making sure to fill in any gullies that were created by the rushing water. If there is more than eight inches of silt, Self suggests that the property owner find a way to have the deposited silt removed. He says that some property owners have even made a profit on removing the silt by selling it as filler.

“Trees can be greatly impacted if they are smothered with this silt material that comes down as a result of the flood. When trees are covered around their trucks, even just a few inches, it can change the whole natural dynamics of the tree, which puts it under stress,” says Self.

Tom West, head grower for Unity of Boulder Sustainable Living Project, says that they got lucky. Although, their gardens were fully submerged by three inches of floodwater, they only had a little over an inch of silt deposit. They have tilled the land in order to diffuse any drying issues the silt would cause.

According to West, no one was able to make it to the garden for four days after the flooding. On day five they found the garden overcome by root rot, a fungal infection that sets in after the base and roots of a plant have remained waterlogged for many hours. West says they lost the best tomato plants they have ever had, and only managed to salvage some of the storage winter squashes, but there was really nothing they could have done once the root rot set in. However, saving the soil for the next round of seasonal crops was very plausible.

According to Self, lab tests indicate that no harmful contaminants or heavy metals are present, but overall the soils are depleted of nutrients.

“The soils were pretty low in nutrients, low in nitrogen, phosphorus and potassium. They were silty soils from the canyon area, washed out and bleached with a lot of water as a result of the flood; the nutrients, almost all flushed out. If you start a garden for example, you are going to have to add fertilizer to the soil in order to improve the quality,” says Self.

The CSU Extension lab provides suggestions on which fertilizer to use depending on what levels of nutrients come back low in the soil sample. Self says that gardeners will generally need to add an all-purpose fertilizer that contains nitrogen,

phosphorus and potassium, but if they prefer to go the organic route, a manure-based fertilizer will work as well. He considers manure a great fertilizer to use because it will also add salts back into the soil that were flushed out.

“… I approach this as what they did 150 years ago; they didn’t go to the store and drop a thousand or two on nutrients. Instead we take the chicken manure, mix it with the straw, get some used marijuana dirt; we layer them all, about six layers, and cover it for six months, turning it along the way,” says West about his fertilizer practices.

At the Unity of Boulder Sustainable Living Project, chickens are fed leaves that have been partially eaten by insects, producing manure for the compost. Plant remnants get heaped onto the compost pile as well, showing how all of the nutrients in their garden get recycled for future use. To West, this is just another regular season. The cooperative garden digs out used soil and replaces it with their composted soil mix every year because the plants suck out the viable nutrients. West says it’s a great way to avoid tomato viruses as well.

Although the CSU Extension lab has not found any serious contaminants in the soil and water tests, Self suggests that gardeners might want to check with their neighbors to see if they had any septic issues because of the flood. He says that contamination worries have diminished by now because enough time and cold weather has passed for the microbes in the soil to not cause any issues, especially if the property received adequate amounts of flood waters to flush the contaminants out.

The tests are a safety precaution when it comes to contaminants, but can be a helpful tool in determining if deposits should be removed and what fertilizer will help restore the soil the best way possible.

“To grow plants in this now, everyone is going to have to beef up the soil in order to make it more productive,” says Self. “Monitoring their garden sight, so if they notice any yellowing in the plants as they start to grow, to address that by adding nitrogen to the soil. Basically, they will have to manage it a little bit more than they have in the past because of the changes that happened.”