Abstract: The invention teaches a stone/soil urban tree mix that can safely support pavements yet also provide ample rooting area--a current limitation--for street trees that are planted close to the pavement. By expanding the rooting zone, the mix allows increased tree growth, decreased tree mortality, and decreased sidewalk failure. The mix employs a stone aggregate that is coated with an acrylamide hydrogel slurry, creating matrix pores that suspend the soil that is added to the mix in specific amounts. The criterion for determining the critical stone to soil dry-weight mixing ratios for various stone and soil types are disclosed.