From the often despicable SF Weekly comes a story about reclaiming urban land for green purposes. Apparently there are laws on the book that will allow you to tear up the sidewalk in front of your property--even if you are a renter so long as you get your landlord's signature. PlantSF, an organization dedicated to urban renewal, will even link you to the forms you need to alert the city of your plans.
There are, of course, several catches: 1. There must still be four feet of sidewalk left for people to walk on, and 2. There is a one-time fee of $215 (less if you can get more of your neighbors to go along with your plan).
Certainly, this will take some time to recoup your investment (especially if bums or other interlopers run off with your crop), but what a great way to turn some worthless concrete into some productive green space. And if you have received a 30-day Notice to Repair from the city, then there really is no excuse not to put that repair money toward the permit fee.
PlantSF will hook you up. Get on it.