Quantifying the effects of pH on the growth of fresh-cut hydroponic culinary herbs
Date
2025-08
Authors
Kramer, Hannah Lynn
Major Professor
Advisor
Currey, Christopher J
Haynes, Cynthia L.
Delate, Kathleen
Committee Member
Journal Title
Journal ISSN
Volume Title
Publisher
Abstract
In hydroponic systems, the nutrient solution pH effects nutrient availability, uptake efficiency, and overall plant growth. Despite this, few studies have systematically evaluated how a range of nutrient solution pH levels affect the growth of fresh-cut culinary herbs in hydroponic systems. This research aimed to quantify the effects of hydroponic nutrient solution pH on the growth, morphology, and tissue nutrient concentrations of four commercially important culinary herbs: basil (Ocimum basilicum ‘Nufar’), dill (Anethum graveolens ‘Hera’), parsley (Petroselinum crispum ‘Giant of Italy’), and sage (Salvia officinalis).
In the first study, herbs were transplanted into one of six deep-flow technique (DFT) systems in a greenhouse with different pH treatments: 4.5, 5.0, 5.5, 6.0, 6.5, and 7.0. Plants were evaluated for shoot and root biomass, morphology, chlorophyll content, and tissue nutrient composition. Growth was generally suppressed at pHs of 4.5 and 7.0, but especially at 7.0. The optimal pH for growth varied by species, and was 5.5 for basil, dill, and parsley, and 6.0 for sage. Basil also tolerated a broader pH range (4.5–6.5), compared to narrower ranges for dill and parsley (5.0–6.0). The results of this study indicate herbs may be able to grow throughout a broader range of pH values than originally thought, if nutrients do not become limited, and inform pH management practices for hydroponic herb production.
In our second study, our objective was to better understand how the growth of culinary herbs is impacted by supra-optimal pH and determine if supplemental micronutrients are an effective mitigation technique. Herbs were grown in nutrient solutions with a pH of 6.0. 7.0, and 8.0, and either with a 1x micronutrient concentration, or a 2x micronutrient concentration. While high pH decreased dill, parsley, and sage shoot height, width, and fresh mass, providing supplemental micronutrients in the nutrient solution did not mitigate growth suppression induced by high pH. This study indicates nutrient solutions with a high pH can severely limit the growth of culinary herbs. While providing supplemental micronutrients does not alleviate the impact of high pH, producers can rely on other methods, such as acid injection, to lower the nutrient solution pH to maximize nutrient uptake.
Series Number
Journal Issue
Is Version Of
Versions
Series
Academic or Administrative Unit
Type
thesis