As we established in a previous blog, a Smart Wetland needs to have a healthy, diverse native wetland plant community. The designed water depths are perfect for emergent marsh vegetation. Emergent plants are rooted in the soil, but their leaves and stems stick out of the water. Plant species have different water depth preferences, ranging from saturated soils to 4 feet of water. There are three ways of establishing a wetland plant community: natural regeneration, seeding, and transplanting.
In the Smart Wetlands, where the base growth media is hydric soils (an indicator of an existing or former wetland), there may be a native seed bank remaining. Even if the land has been farmed for over 100 years, the seeds from the wetland plants that once inhabited the area can still be present and viable in the soil. Just add water and instant wetland! Well, not quite that easy, but natural regeneration is the least expensive and labor-intensive way of establishing a plant community.
However, some former wetland areas may have been planted with non-native species for hunting purposes back in the day. These wetland plants may flourish in the first years as they typically prefer saturated soils. But once the final operating water levels are set, they are outcompeted by the native plants since they can’t typically thrive under 12-18” of water. Additional seeding or transplanting of plants may be needed to fill out the wetland area if the plant community doesn’t fill it out or lacks diversity.
For Smart Wetland sites constructed with upland soils as the base soil in the wetland, we establish the plant community through seeding and transplanting before raising the water level. The species selected are based on the different water depths within the wetland. Seeds and plugs (rooted seedlings) are purchased from several reputable local nurseries or collected from one of our other Smart Wetlands.
Transplanting purchased or collected plant plugs is the quickest and most reliable way to develop the plant community. The plugs should be planted at a minimum of 4-foot by 4-foot spacing. While seed germination can be unpredictable, it is much more cost-effective and less work than relying solely on transplanting plugs. Some plants do well via seeding, while others do not and should be transplanted, such as common arrowhead.
Like with growing corn or soybeans, timing is everything with wetland plants. If the wetland is ready within the early part of the growing season, we will rely on plugs initially and then supplement with seeding the following winter. Planting in the mid-to-late spring gives the seedlings a long growing season for root and shoot growth. However, if we finish construction at the end of the growing season, we will seed in the winter (known as frost-seeding) and do a few transplants in late spring.
Why frost-seed in the winter? While we love wearing our insulated bib overalls and playing in the snow, that isn’t the reason. Most native wetland plants in the Midwest need repeated freeze-thaw cycles, or cold-moist stratification, to germinate. Seeding between December and March, when temperatures are typically below 40° F, allows for several months of stratification in cold and damp conditions. Most native species need 30 to 90 days of cold-moist stratification to germinate.
By hand we will broadcast the seed out onto the iced-over or snow-covered wetland bottom. Since wetland plant seeds are very small and light, we mix them based on their water depth preferences with a carrier such as sterile sand or sawdust. The carrier ensures the seed reaches the ground and contacts the bottom wetland soil versus being blown away in the wind to the neighboring field. When the temperatures warm up in the spring, we ensure the soils stay moist, and the seeds receive direct sunlight for the seedlings to develop. As the seedlings grow, we incrementally raise the water levels so that the tops of the plants remain out of the water. By August, the water level is set at the normal operating depth for the Smart Wetland. Over time the community will fill out, and all the various species will thrive.
Watch as our Livingston County #1 Smart Wetland transforms over from bare soil to a thriving wetland thru natural plant regeneration, seeding, and transplanting.
Jill Kostel leads the project team as TWI’s Senior Environmental Engineer and primary designer of Smart Wetlands. She also works to develop new partnerships to help spread constructed wetlands widely in Illinois.
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