by Layne Knoche, Landscape Designer
Last fall, the RORG team and nearly 100 volunteers successfully installed about 9,000 native plants at the rain garden. While this monumental feat sounds like a lot, it might not look like a lot to many folks accustomed to HGTV quick transformations. That is, it might not look like much yet.
In order to work with our budget, we couldn’t bring in 9,000 plants typical to what can be seen at most nurseries. We ordered nearly all of these plants (with the exception of shrubs and two forb species) in “cell trays.” These 12″ x 24″ trays hold anywhere between 32 and 50 plants that were grown in single cells. Yes, spending less was a factor this decision, but the project’s budget was not the only factor in our decision to use small plants. In fact, the best part about these plants had nothing to do with budgeting at all!
“Real landscapes are slow grown.”Thomas Rainer & Claudia West, Planting in a Post-Wild World
Plant Plugs: The Best Approach for RORG
First of all, let’s talk about a few practical reasons for why we went with plugs instead of larger plants. We were able to fit all 9,000 of our plants into two greenhouse rooms. This was very helpful, especially since installation took multiple weeks and the plants still had to be watered and maintained while awaiting installation. If all our plants had been in even quart sized containers, we would have needed substantially more storage space, leading to more maintenance, time, and money. It also would have been more difficult to move everything from the greenhouse to the site for installation. To give you an idea, when moving quart-sized plants, we could fit roughly 60 plants on a single cart. When using the trays, we could easily fit 400! This helped reduce the number of trips our team and volunteers had to make back and forth from the greenhouse to the garden.
While on the topic, we want to note that the University of Illinois Greenhouse staff were amazing to work with throughout the garden installation and we continue to work with them today on other projects. They’re a wonderful asset to have on campus.
Another benefit of using plugs at the garden was the ability to install thousands in a single day. Take Pennsylvania Sedge, Carex pensylvanica, for example. We installed 1,600 plugs of that species alone, along with hundreds of plants of other species. In total, we probably installed close to 3,500 plants in two days! As discussed in previous blog posts (here, here, and here), this was accomplished by using handheld battery-operated power drills with auger attachments. While extremely repetitive, drilling holes was certainly easier and less time consuming than having to physically dig holes for larger sized plants (trust me, I know!). This was also helpful in preventing damage to the existing roots under the trees’ canopies.
The Best Benefit
Everything discussed so far are nice perks, but perhaps the best reason for using plugs has to do with the plants’ adaptability to specific site conditions. Thomas Rainer and Claudia West are the authors of Planting in a Post-Wild World, which greatly influenced this redesign of the Red Oak Rain Garden, and they do a fantastic job of detailing why smaller plants generally perform better in the long run.
Establishing gardens doesn’t mean bringing in huge plants that will give instant visual gratification. A huge piece of the establishment puzzle comes down to what’s going on underground in the root zone. Plants are more likely to thrive when they develop in site-specific soils from an early age. The standard for growing seedlings in nutrient rich “candy” soil media makes for quick and easy growth from the beginning, but the larger the plants get in the containers they’re grown in, the more susceptible they are to damage once planting occurs. Root damage, especially when dealing with taproot species, can ruin the chances of plant survival. To combat this, plugs generally have deep cells that allow for our native plants to begin putting down those deep roots they need to survive hot, dry weather.
Once the plant plugs are installed, the new soil will almost certainly be less fertile than the soil the plants were started in. Using plugs means the plants won’t need significant soil amendments to survive like larger potted plants may need. Their roots will be forced to expand into the surrounding soil to survive. I know this sounds harsh, but it’ll help them in the long run, I promise! (Side note: always test your soil before installing a garden so you can become familiar with your specific conditions. Knowing these conditions can help you select which plants will do well and which plants will not)
So this leads to the final question: when will the Red Oak Rain Garden look like a garden?
“Sleep, Creep, Leap”
Native plants’ first three years can be described as the “Sleep, Creep, & Leap” years. This first year of establishment, the garden may appear to be “sleepy,” as not much above the surface seems to be happening. Sure, there will be a lot of green and maybe even a few blooms here and there, but the real show will be happening underground. The 9,000 plants will be spreading out their roots, developing their methods of nutrient intake, drought tolerance, and fire resistance (no, we won’t be burning the garden since we’re in the middle of a university campus). These are the roots that will eventually help filter out the nearly 3,600 ft³ of stormwater the garden holds at capacity.
The second year, you’ll start to see the garden plants filling in as they begin to “creep.” This is an important step in the design concept of the Red Oak Rain Garden. The garden was planted densely for aesthetic and maintenance purposes. The green carpet of varying textures, colors, and forms will set the stage for the not-too-distant floral show above. It will also help to shade out weeds that try to pop up in the garden.
The third year is when the plants “leap.” Floral displays will become more impressive and the plants will continue to develop both above and below ground. By this time, the plants will be attracting pollinators and functioning as sources of food and shelter for insects, birds and other species, all while providing service to us humans by reducing flooding caused by heavy rain events. In other words, the garden will finally look like a garden. Maybe even one better than those on television.