Suitability of Sedum Japonicum in Rooftop Environments
Sedum Japonicum was the first sedum that captured my interest. It's a bright yellow Sedum with beautiful star-shaped leaves aften called "Tokyo Sun" by various cultivars. My goal at the time was to find a groundcover for my columnar cactus, to keep the weeds at bay (while avoiding the less aesthetic option of mulch or surface rocks). As such, I purchased about 80 trays of Japonicum and started the work of propagation and covering my garden with the plants.
At first, the yellow Japonicum looked beautiful in my garden. Unfortunately, the hot summer sun did a number on the plant, causing it to shrink in size and die off. In an effort to save my remaining plants, I built a shadehouse and moved the vast number of plants to that location.
In the shade and with supplemental water, the Japonicum recovered. My hope was that after recovering the sedum, and gradually introducing them to the sun this time, they would be able to thrive.
Unfortunately, once I moved the Japonicum back to the sunnier location and gradually reduced the water to zero-maintenance levels, the Japonicum began to whither and die again.
However, I noticed a strange occurrence. In some of the trays, I found Japonicum that was green instead of yellow. It must be a sort of mutation. In addition, this sedum was firm to the touch, and not flimsy like the dying yellow sedum.
Accordingly, I sought to propagate and cultivate the green Japonicum. I grabbed many samples the healthiest green Japonicum and carefully transplanted them to my shadehouse. With extra care, both green and yellow sedum recovered and thrived. Sometimes I would notice a yellow sprout up in a sea of green, and sometimes the opposite occurred.
As I continued to propagate the green sedum, I more and more consistently got 100% green Japonicum.
Now with a large stock of exclusively green Japonicum, I felt that I was ready to subject the plant to harsher conditions with more intense sunlight and less water. I was thrilled with the result!
When under stress, both yellow and green sedums shrink in size (presumably to conserve resources). The green sedum also gained a yellow/red tint as it got firmer to the touch. However, unlike the yellow sedum, the green Japonicum did not die off. Instead, it shrunk, got firmer to the touch, and most importantly, continued to grow new shoots. Eventually, I was left with an incredibly dense and hardy Japonicum plant!
When under reduced stress, the green sedum Japonicum forms a dense emerald-green mat that effectively blocks out weeds! I now had a hardy groundcover sedum that was zero-maintenance and kept the weeds away from my columnar cactus. In addition, this plant grew beautifully in my rooftop wicking box.
As a result of this success, I continue to propagate this green Japonicum for both rooftop environments and ground cover. It is also available at the store.