Garden Experimenting

Picture below is from our raised garden bed. I did a mini-experiment with some of our biologicals and took last year's leftover Johnson-Su extract remains and mixed it in soil. Plants are thriving but almost 0 seeds will germinate. 1 weed germinated. I planted peas and lettuce and got 0 to germinate. The lettuce and broccoli were from a nursery, gifts from a friend. Trying to figure out the biology of this, no weeds is great, no plant germination, not so much!