These tiny sweet peas grow in 1/2 my beds and I've noticed that the Iris produce DOUBLE where they grow... Think they are putting nutrients in the soil?
"Hairy vetch is a legume used primarily for soil improvement along roadsides and for bank stabilization. Well-nodulated hairy vetch can enrich the soil with 60 to 120 lb/acre of nitrogen through nitrogen fixation. Later seeded vetch grown as a cover crop for green manure, will supply a smaller amount of N."