There is no way to overstate the profound effect of the August 2020 derecho on the greater Cedar Rapids area. It will always be mentioned in the same breath as the 2008 flood in terms of the power displayed by Mother Nature, and the raw destruction of its force.
It’s been estimated that Cedar Rapids has lost more than 80% of its tree cover since August 10, 2020. That number continues to grow as trees that were damaged, but not destroyed, by the storm eventually succumb to irreversible harm. Great efforts have been made to replant lost trees, but it will take decades for the city to resemble what it once was. The environment around us has changed considerably, and we’ll talk about the different issues and opportunities that have arisen.
Effects of Sun & Shade on Lawn Grass
For decades, lawns and landscapes around Cedar Rapids sat under an umbrella of shade. This influenced so many decisions that homeowners encounter when planning their outdoor space. The types of landscape plants that do well in shady conditions are certainly not the same as those that do well in full sun. The same thought applies to turf grass! We can’t pick grass types based simply on what we want or what looks better. The selection must be made for the specific environment. Older, shaded lawns in our area will have a high percentage of “fine-leaf” fescues. Some very old seed blends that were marketed for shady growing sites also contained “rough bluegrass”. When we communicate with customers about that type of grass, we will refer to it as poa trivialis, its scientific name. All the mentioned grasses are tolerant to shade, have a very fine leaf texture, and are adapted to cooler temperatures. Even under the cover of shade, hot and humid weather in the middle of summer will cause poa trivialis and fine fescues to show signs of stress. Their leaves will become brown, vigor is lost, and the overall appearance is mistaken for disease. This stress is usually temporary, and by fall everything looks green and healthy again. With no shade cover, these grass types are now in a losing battle. Many homeowners in Cedar Rapids are seeing this, and the ultimate solution most of the time is to re-seed or sod the lawn with grasses that do well in full sun environments. Replacing the shade would be great, but it will take decades to accomplish that.
New Weeds Arriving Post-Derecho
In August, many plants have sprouted seed heads, including weeds. Seeds are designed to travel, and they are most often moved by the wind. A multiple-hour weather event with straight-line winds exceeding 70 MPH, traveling across hundreds of miles, is certain to move a lot of seeds! We saw the results of this migration in the spring of 2021. Our customers and technicians were shocked by the amount of weeds found in lawns, but we were all baffled by what we were seeing too. Field pennycress, marestail, prickly lettuce, garlic mustard….plants that were typically problematic in farm fields and forest floors, were now growing in our lawns. I’ve pictured them below:
Garlic Mustard (In year 1)
Garlic mustard is an invasive plant that has been taking over forest floors for several years. It doesn’t do well in full sun environments, so in that regard it has declined in the wooded areas of Cedar Rapids. Where it concerned us was that the sheer abundance of seeds was causing it to pop up in landscaping beds and in thin areas on shaded lawns.
As the season went on, we found that periodic applications of broadleaf weed control and regular mowing were effective in getting rid of these weeds. We did see them emerge again in 2022, and prickly lettuce, in particular, has become one of the weeds seen most often by our technicians. Again, we are encouraged by the control that has been achieved with our broadleaf weed control.
Planting New Grass & Trees
After losing so many trees, the natural reaction has been a city-wide effort to replace them! Thousands and thousands of new trees have been planted in the last 2 years, with many more to come. When planting a new tree, nurseries stress the importance of watering. Without a doubt, consistent watering is imperative. Fertilizing the root zone is extremely beneficial, and growth rates can be increased up to 20% by giving the plant supplemental nutrition. Iowa soil is known for being fertile and offering a great medium for plant growth. When trees are transplanted, it can take time for roots to transition to their new home and thrive. Deep root fertilization helps hasten that process. Root growth and top growth (leaves and branches) maintain a balance. When the root growth is boosted, the plant absorbs more nutrients and water which are turned into leaves and branches. The extra foliage produces more carbohydrates which are sent to the roots to enhance root growth. It creates an efficient, productive “machine” that builds on itself and the end result is a healthier plant that will reach maturity sooner.
Plant selection and placement is important when trying to replace trees that have been lost. There is usually a desire to put the same kind of tree in, but several factors should be considered before planting something new. Many of the older neighborhoods in Cedar Rapids were filled with large, stately oaks that were likely there before. Most of the oaks native to Iowa are in the white oak family, which are slow growers. If the goal is to re-establish some shade, a faster growing species should be considered.
Transitioning from Trees to Grass
When trees came down, they left behind stumps that required grinding out and cleaning up. It’s not recommended to plant new trees in the same spot as an older tree that was taken out, so the holes left behind needed to be converted to new grass cover. The first challenge was making sure the stump was thoroughly ground down and as much wood material removed as possible. While a stump is being ground out, it’s difficult to see exactly where the large surface roots of a tree are since they become covered in debris. Those surface roots, if not thoroughly removed, will continue to be a nuisance until they are completely removed. With the tree (its anchor) now gone, they are more likely to come up out of the soil during our usual freeze/thaw cycles in the spring. Those exposed roots are not only an annoying eyesore, but they can be a tripping hazard and potentially damage mower blades.
With a large hole left behind, the steps to establishing turf seemed very straightforward! Add some soil, level and grade, then seed or sod the area. However, it was more of a challenge than we anticipated. One factor was the difficulty in clearing all wood material from the old stumps. It seemed that no matter how many wood chips and shavings were removed, more always seemed to bubble up to the surface. Grass can’t sustain growth in a soil that has a large percentage of wood material. Those wood chips have not broken down into organic matter yet that can sustain plant growth, and as they decay, air pockets are created. Those air pockets lead to instability of the soil, and until that soil has fully settled, roots cannot thrive in that environment.
Another reason it has been so difficult to establish turf where large trees once stood, is methane. When large amounts of organic matter decompose, methane gas is released. An overabundance of that gas is toxic to young roots that haven’t fully established. Therefore, we still see areas that are struggling to grow grass more than two years later. Unfortunately, this wasn’t learned about or realized until the spring and summer of 2021, when it was clear that something wasn’t working. Over time, we can expect things to keep decaying and turning into nutrient-rich organic matter. The amounts of gas given off should subside, and the growing medium will support turf growth. How long that will take is anyone’s best guess.