I think that might be a zucchini plant growing just behind the rubble. I only noticed it a few moments ago while looking at the scan. Havana is internationally known as a leader in urban agriculture and community gardening so I looked around in Santiago hoping to see some of the same. I think we might have found some had we been able to see more outside the core of the city. We did see one from our bus ride to the airport on the way out of Cuba. It was in front of an apartment block located on the outskirts of the city where there was a lot of open land.
This empty lot was a bit of an anomaly in the areas we covered. The only available green space or empty space for that matter were a handful of public parks or squares. People had almost zero space outside their homes sitting between the sidewalk and the street so we only saw the odd container garden and they usually contained flowering or foliage plants.
I have so much regret that we didn't get into the city one more day for further exploration but we just didn't have enough time and other factors were working against us. A week is great for relaxation but not enough time to really see a place.