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ISHS Acta Horticulturae 1334: II International Symposium on Tropical and Subtropical Ornamentals

Controlled release fertilizer and soilless medium temperatures significantly interact during greenhouse production of Philodendron ‘Imperial Green’

Authors:   J.L. Griffis, M.M. Manners, Q. Barnes
Keywords:   CRF, DLI, daily light integral, HOBO, Nix Pro Color Sensor
DOI:   10.17660/ActaHortic.2022.1334.35
Philodendron ‘Imperial Green’ is a commonly produced foliage plant in central Florida, but only general fertilizer recommendations for philodendrons are available to growers. Tissue-culture plugs of Philodendron ‘Imperial Green’ were potted up in green 15.24 cm pots using a standard peat/perlite soilless mix amended with dolomite and three rates of Diamond R 19-6-9 fertilizer blend also containing micronutrients and SureTRX, a proprietary amino acid additive. This controlled-release fertilizer (CRF) is formulated to release evenly over 180 days with soil temperatures of about 30°C. Soilless medium temperatures were measured continuously using Onset HOBO MX2202 Bluetooth Temperature/Light Data loggers buried in several pots. Plants were produced in the greenhouses under either full sun or 30% shade environments. Soilless medium temperatures were generally 1-2°C cooler in the shade during the day, but the temperatures dropped slowly after sunset such that there were no temperature differences between treatments at sunrise. The electrical conductivity (EC) for all pots was measured on a weekly basis using the standard pour-through method to evaluate the overall fertilizer levels available. The fertilizer was exhausted before 150 days in the plants growing in the full sun whereas the CRF lasted about the expected 180 days in the plants growing in 30% shade. Fertilizer stirred into the soilless medium was not affected by greenhouse light levels and all pots received the same automated irrigation treatments. Fertilizer release rates were closely related to the soilless medium temperatures. A small diurnal variation in soilless medium temperature had a considerable impact on fertilizer release rates over the full time of the experiment. Plants grown in full sun grew larger more quickly than plants produced in 30% shade for all fertilizer rates, but plants grown in 30% shade were a darker green color (as measured using a Nix Pro color sensor) for all fertilizer rates.

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