Effects of Soil Amendments and Biostimulants on the Post-transplant Growth of Landscape Trees
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.