Fill the gutters with soil to be about half full.
Deep gutters for planting.
Succulent plants generally have spreading roots and grow perfectly in shallow containers such as a portion of gutter.
You can grow shallow rooted annuals greens herbs and plants nasturtiums in this setup.
You should have enough gutter downspouts to effectively handle the size of your entire gutter system.
The best garden gutter plants are those with spreading roots instead of those that continue to grow downward.
This will allow the excess water to be drained.
For this you can even install partial gutter systems which are less expensive and can be positioned to only manage the flow of water in certain areas.
A far more relevant reason to install gutters on southern california homes is to direct water away from outdoor living areas walkways porches and doorways.
Dress up your boring wooden fence or walls using aluminum gutters following this idea.
Besides the plants already mentioned you can try.
Drill small holes in the bottom of the gutters.
Add some fertilizer and fill the rest of the gutter with soil.
Cut a section of gutter 4 to 6 feet long using tin snips for metal gutters and a pvc handsaw for plastic gutters.
A good rule of thumb is to install one for every 35 or so linear feet of gutter.