By Andrew Yanders
E. King Fire Station after receiving 70 lbs. of Sedum Cuttings. Five varieties of cuttings were spread that day and 6 varieties of herbaceous plugs
Last week I traveled to the City of Lancaster to oversee the install of 155 lbs. of Sedum cuttings on the Dewatering Building and E. King Street Fire Station green roofs. Both green roofs were installed earlier this year during the winter months. The Dewatering green roof was installed January 22nd through the 25th and just under two months later Fire Station green roof was installed.
There is a common misconception that green roofs cannot be constructed and vegetation planted during the winter months. Actually, we believe installing green roofs when spring is just around the corner is ideal. The weather may not be to the likely of many fair-weather green roofers, but for those who are willing to brace the cold and wet, the payback for the client is well worth it. By establishing the vegetation in its new soil media prior to the start of the growing season, plants are able to jump start their growth and the first 2 months of the growing season can be equal to more than 6 months of growth if the same plants were planted later in the year. Unfortunately, too often vegetation (in this case the Sedum cuttings) is not available until the spring when it is more advantageous for the nursery.
It was so cold the week we installed the Dewatering Building’s green roof that the growing media and Sedum mats arrived frozen solid. The growing media had to be defrosted overnight inside the garage portion of the building and the Sedum mats that could not be unrolled were left out in the sun for one day. Despite being completely frozen prior to install, the health of the Sedum mats was not compromised at all.
There is one detail that must be given special attention when planting during the winter months. When planting plugs, it is critical that they are planted as deep as possible. If this requires loosening or removing a portion of the bottom, so be it. But if they are not planted deep and the soil well compacted around them, then plugs will migrate up out of the soil during periods of freeze and thaw. This can happen to the extent that a plug becomes completely removed from the soil, exposing the root system to the elements, and often results in the plug withering and dying. Plugs are not cheap and a negligent planting technique is a waste of the client’s money.
The color of the Sedum mats on the upper portion of the Dewatering Building's green roof has changed from mostly reds to a variety of lush greens. New growth is abundant.
Preparing the soil for Sedum cuttings is critical. Because the soil was installed several weeks prior, the top layer of the soil needed to be loosens and leveled. This increases the contact area between the soil and the cuttings, promoting more abundant rooting.
Even though there was a light rain while spreading the cuttings, we still watered the green roof. We wanted to ensure there was uniform moisture throughout the roof, but also the moisture helps to hold the cuttings in place until they begin to root out in a few days.