Use of soil amendments at planting is one of the time-honored traditions in horticulture, although their effectiveness has been questioned by many. Recently, humate and humate-based products, generally known as biostimulants, have been marketed to increase transplant success. In this study, three experiments were conducted to examine the effects of soil amendments and biostimulants on post-transplant growth of landscape trees. The first experiment, conducted in a greenhouse, determined the effects of several biostimulant treatments (granular humate, water-soluble humate, liquid humate, liquid humate+ = humic acid, hormones, and vitamins) and fertilizer levels (low, medium, high) on the growth of container-grown Corylus colurna L. (Turkish hazelnut) seedlings. Biostimulants did not increase top growth compared to control treatments, but root growth was increased by granular humate at a medium fertilizer rate. The second experiment examined the effects of biostimulants (granular humate, water-soluble humate, liquid humate+) on the post-transplant root growth and sap-flow of landscape-sized balled and burlapped Acer rubrum L. (red maple) grown in root observation compartments (rhizotrons). Biostimulants did not increase root growth over control treatments, but sap-flow was increased. The third experiment, conducted in the field (Groseclose silt loam soil) investigated the effects of soil amendments (peat, and compost) and biostimulants (granular humate, and liquid humate+) on the post-transplant growth of Crataegus phaenopyrum (Blume) Hara (Washington hawthorn) and red maple transplanted bare-root, and grown under combinations of irrigated vs non-irrigated and fertilized-at-planting vs non-fertilized-at-planting regimes. Hawthorn controls generally had less top growth than the other soil treatments as a whole. No soil treatment was higher than control for top growth of red maple. However, root growth of red maple was highest in the peat-treated trees. Stem diameter and dry mass for the control and compost treatments were higher than the biostimulant treatments in irrigated plots, but no differences were observed in non-irrigated plots. Granular humate-treated trees resulted in higher stem diameter and dry mass than the liquid humate+-treated trees in non-irrigated plots. There were no effects of fertilizer, or irrigation on growth after two growing seasons for either species.