BIOSTIMULANTS AND SOIL AMENDMENTS AFFECT 2-YEAR POSTTRANSPLANT GROWTHOF RED MAPLE AND WASHINGTON HAWTHORN

Humate-based products have been aggressively marketed as biostimulants that increase plant growth. Little data are available on their effect on tree establishment or their interaction with fertilizer and irriga tion regimes. This experiment tested several types of biostimulants on posttransplant growth of Acer rubrum L. (red maple) and Crataegus pha enopyrum (Blume) Hara (Washington hawthorn) trees, both with and witho ut irrigation and fertilization. Soil treatments were applied at plant ing as: 1) control (native backfill only); 2) compost (native backfill + yard-waste compost); 3) peat (native backfill + Canadian sphagnum p eat); 4) granular humate, 100 g/tree; 5) granular humate, 200 g/tree; and 6) liquid humate +, a proprietary liquid mixture of humate, kelp e xtract, thiamine, and intermediate ''metabolites.'' Irrigation regime x soil treatment interaction was significant for red maple, but soil t reatments did not increase height, stem diameter, top dry mass, or roo t length. For Washington hawthorn, soil treatments did not increase he ight, stem diameter, or root length, but top dry mass in all treatment s as a group and in humate-treated trees in particular was greater tha n that of controls. Roots of peat-treated trees of both species were l onger than those in other treatments. Granular humate applied at 200 g /tree increased total root length more than did 100 g/tree in Washingt on hawthorn but not in red maple. Fertilizing at planting with N at 14 .5 g.m(-2) had no effect on any parameter measured for either species.