I love to plant sunflowers of different types and, at the end of summer, leave the sunflower heads to ripen and feed the birds. The birds make a mess when pulling the seeds out of the sunflower head, but nonetheless, it's quite entertaining to watch. The next spring, I'll typically find a few sunflower volunteers from seeds that were overlooked in the fall.
So this past spring, I wasn't too surprised to find some volunteer seedlings growing outside my raised vegetable bed in the compacted gravel path. I left the seedings alone and didn't think too much about them. I assumed that they would wither and die without good soil and a water source.
I was wrong.
The sunflowers grew and grew! I quickly figured out that seepage from the raised bed provided their water source. But growing in compacted gravel and not soil? This was new to me. I didn't have the heart to pull them out when they were trying so hard to grow under adverse conditions and so I left them in place as an experiment. It turns out that sunflowers aren't fussy about soil conditions as long as the location is well-drained. Of course, the plants will better reach their maximum potential with better, nutrient-rich soil.
Ultimately, I had a pair of beautiful 12-foot tall, multi-branched sunflowers in my gravel path. It was in an interesting experiment and I wonder how well the plants would have done in better soil!