Effects of Above-Ground Pot-in-Pot (PIP) Placement and Humic Acid Extract on Growth of Crape Myrtle

Abstract

Abstract Rooted cuttings of crape myrtle (Lagerstroemia indica L. × L. fauriei Koehne ‘Muskogee’) were potted into 3.8 liter (1 gal) black polyethylene containers and subjected for two months to one of three above-ground shielding treatments; containers placed pot-in-pot (PIP) for two months, containers exposed to direct sunlight for two months, or containers placed PIP for one month and then exposed to sunlight for one month (PIP/exposed). Mean daily maximum temperatures in rooting substrate of containers exposed to sunlight were as much as 16C (29F) higher than PIP containers. Plants in containers exposed to sunlight for two months had less total root and shoot length and higher concentrations of leaf nitrogen compared with the other two treatments. Plants were next transplanted into 27-liter (7-gal) polybags filled with a landscape substrate and fertigated with a humic acid extract at 0, 50, 150, or 300 μL/L for two additional months. The change in shoot and root length of plants previously placed PIP for two months responded in quadratic fashion to increased humic acid extract concentration levels; the most response occurred at about 50 μL/L while the highest concentrations inhibited post-transplant growth. Growth inhibition caused by heat stress as a result of exposure of container walls to insolation was still evident two months after transplanting.