I did a post on sunflowers on the 9th of March about sunflowers taking position on vegetable beds. These sunflowers are really going into the second generation.
Now they grow at different locations. The majority stay on the same vegetable as the mother plants used to be. These somehow suffer from pest attact, grasshoppers mostly. The other six sunflower plants are on tomato bed, which grow better. The leaves are wide and big. Other than the fact that they experience positive effect from tomato plants nearby, the bed was in fact previously occupied by winged beans plants.
Winged beans are able to 'fix' the all important plant food Nitrogen from the atmosphere. This is stored in small but visible 'nodules ' on the root system, and is often left in the soil after the plant's death. The Nitrogen is obtained from the atmosphere by a symbiotic relationship with the nodules and certain bacteria (Rhizobium). For that reason, the soil is now very fertile in that bed.