If one or two species of plants seem to be taking over, you can add clippings or plugs of other plant varieties to re-establish them on your roof. To get those new plants growing, select a growing medium or soil already mixed with an organic fertilizer that will benefit the plants you’re installing. Gingko Sustainability, a green roof installation company in Ontario, suggests testing your growing medium in the spring to find out which nutrients your plants might be lacking. Your installer or local nursery will have suggestions on which nutrients are best, how to incorporate them into your roof soil, and how often.
For sedum roofs, Gingko Sustainability recommends an NPK ratio (nitrogen, phosphorus, potassium) of 5-2-6. The numbers indicate the nutrient concentration (the higher the number, the more concentrated the nutrient). Most commercial fertilizers are higher, but the recommended NPK ratio for green roofs is lower to avoid over-fertilizing, burning the plants. And you can always add more.
Annually, check the drainage system above or below your waterproof membrane or green roof modules. Look for backed up water after a hard rain that’s puddling or pooling. Popular drought-tolerant live roof plants, like sedums and other hardy succulents, can become diseased or drown if left in water. Some live-roof systems utilize modular panels that homeowners can easily lift to check for leaks and standing water. Also, keep gutters free of leaf debris and tree seedlings, and downspouts clean and in good repair. Even though green roofs absorb much of the water, extra water still needs someplace to go.
EcoBrooklyn Living Walls also suggests making sure drainage areas are clear of plants. Many people like to plant to the very edge, but keeping a clean border around the edge, especially near the drain outlets, helps keep the drains clog-free.
Companies that install and help maintain living or green roofs suggest that homeowners keep a detailed maintenance log or diary. Include photographs of the green roof every time you weed, water, fertilize, or do other maintenance. Make notes on plants that are thriving and those that aren’t. Take the photos from the same location and with the same view throughout the seasons to track changes. Use those photos, and your notes, to record the effectiveness of weeding, fertilizing, watering, and even supplemental planting. The diary will also keep you on schedule for routine maintenance.
For most homeowners, green roof maintenance isn’t too tasking or difficult. Just be sure to utilize a steady ladder to access the roof. Be sure to have someone who can spot you from the ground in case of difficulties. Plan your green roof maintenance for cooler days. Of course, homeowners can always outsource roof maintenance chores to green roof or landscape professionals. However, part of the joy of having a green roof is getting up top to enjoy the blooms and butterflies—the winged fruits of your labors in planning, planting and maintaining a garden in the sky.
