Be aware that you are also obligated to notify PG&E at (800) 227-2600 before digging around your house or yard. It's essential that a PG&E technician identify and mark the locations of gas and electric lines before you plant any trees. Don't forget to call your other utilities, such as cable and phone companies, as well as the SFPUC (415-551-3099). Making these calls is worth the relatively small investment of time: if you dig without knowing what's underground, you could disrupt service, or worse, cause a fatal explosion.

• See the San Francisco Department of the Environment's outline of Worm and Backyard Composting, which provides useful gardening tips, such as how to determine the most easily sustainable method of recycling your vegetative food scraps and yard trimmings, how to eliminate the need to transport organic material out of the city, how to create a moist, nutrient-rich addition to the soil for your garden and house plants, and how to find a free compost workshop at a local community garden.
  
  For a list of community gardens on public property, see the San Francisco Recreation & Park Department's Web site. You'll also find information about how these cooperative gardens operate and details on getting involved in the one nearest you.
  
  
• Don't forgo visiting some of the lovely public gardens around the city:
  
  
  • The San Francisco Botanical Garden at Strybing Arboretum (Golden Gate Park at 9th Avenue and Lincoln Way) fulfills its mission to "inspire visitors with the extraordinary diversity of rare and unusual plants that can be grown in coastal California." The garden is open Monday through Friday from 8:00 AM to 4:30 PM, and on weekends  holidays from 10:00 AM to 5:00 PM. Take advantage of one of the free docent-led tours given at 1:30 PM daily.
    
    
  • In addition, the Botanical Garden Nursery, located at the southwest corner of the garden, usually holds a plant sale every Saturday from 10:00 AM to 1:00 PM. See the 2008 online schedule for details on featured plants.