Lee Gordon, CNPS San Diego Gardening Committee
Conventional wisdom says that the best time to sow annual wildflower seeds is in the fall, just before the rains, and that seeds should be covered with a thin layer of soil to protect them from predation. This conventional wisdom may be wrong. Tests in Scripps Ranch and Poway (San Diego County) suggest that it is better to sow wildflower seeds months in advance of the fall rain, and that covering seeds may actually prevent them from germinating.
The first test was in my friend Bob’s back yard in Poway. I mixed packets of seeds, and he sowed them in three adjacent areas in July, September and early November. He covered half of each area with a thin layer of soil and left the other half uncovered. The worst results were in the November area covered with soil. The best were from the half of the September sowing that was left uncovered.
I tried a similar test in a small Scripps Ranch open space, dubbed the “Canyonito” by CNPS member Sarah. I sowed seeds in three adjacent areas in June, September and November, leaving them uncovered. Workmen later covered the last two areas with a thick mulch to suppress weeds. No wildflowers grew in these areas at all. However, the area sown in June was left alone, and this area had a beautiful spring bloom. This test shows that you can get good results from sowing seeds early.
In a third less formal test, I sowed wildflowers on a hillside brush management zone in Scripps Ranch in October. This is an area of trimmed chaparral with considerable bare dirt. Two of the species behaved differently here compared with how they grow in the wild. While some plants grew to a normal size, many more grew late and stunted. Plants that grow stunted like these are uncommon in the wild.