It’s a hard life for a young urban tree. It is transplanted from an irrigated and fertilized nursery field and planted in a hot, dry planting strip where it must quickly develop roots. Without irrigation, a large fraction of new trees wouldn’t survive the first summer. SDOT trees, however, get substantial help through the first couple of summers in the form of weekly water. In spring, SDOT crews zip tree gators around the new trees and water each tree once per week throughout the summer. The tree gators, bags made of heavy-duty plastic, hold 15-20 gallons of water, and empty over four hours. The slow draining saturates the soil in the root zone instead of running off the surface and encourages deeper root growth.
Water keeps the trees happy, but means that SDOT tree and landscape crews have their hands full. Each week they water over 1,800 trees. Using our GIS-based street tree inventory, we mapped the trees planted within the last two years. We then divided the trees into twelve routes: three two-person crews watering four days each week. The routes that are more spread out have fewer trees than the more compact routes so that each route can be finished in one day, if all goes smoothly. The watering crews are using Street Maintenance flusher trucks, which are used at night to clean downtown alleys. Urban Forestry staff and supervisors coordinated with their counterparts in Street Maintenance to share the trucks. The 3,000 gallon trucks don’t need to be refilled often, but are a challenge on narrow residential streets. Crewmembers work together to get to all the trees efficiently; one person drags the hose and fills up the bag, while the driver pulls the truck forward as needed. Field crews rise to the challenge, and somehow find a way to get to all those trees each week. Watering is a substantial operation, but literally keeps the SDOT investment in street trees growing.