Strategies to reduce supraoptimal temperatures in the root zone during field and containerized production of highbush blueberry in warm climates

Authors: MACHADO, RUI - University Of Evora; Bryla, David; CORREIA, MARA - University Of Evora

Submitted to: Acta Horticulturae
Publication Type: Proceedings
Publication Acceptance Date: 8/1/2022
Publication Date: 3/21/2023
Citation: Machado, R.M., Bryla, D.R., Correia, M. 2023. Strategies to reduce supraoptimal temperatures in the root zone during field and containerized production of highbush blueberry in warm climates. Acta Horticulturae. 1357:393-401. https://doi.org/10.17660/ActaHortic.2023.1357.55.
DOI: https://doi.org/10.17660/ActaHortic.2023.1357.55

Interpretive Summary: Blueberry roots tend to be sensitive to high temperatures and readily die in warms soils. The objective of the present study was to identify strategies to reduce the temperature of the root zone during field or container production of highbush blueberry in warmer climates. Three experiments were conducted, including two in the field and one in pots. We designed the first experiment to determine whether green and white colored geotextile landscape fabrics could be used in place of black landscape fabric to improve survival and growth of highbush blueberry in regions with warm climates. Green landscape fabric was quite effective at reducing both weeds and soil temperature, and over the long term, may be less costly than bark. White landscape fabric, on the other hand, resulted in excessive weed growth underneath due to transmittance of light through the fabric. The second experiment was conducted to determine whether white pots were better than black pots for producing blueberries in substrate. Substrate temperature was clearly cooler and more stable throughout the day in white pots than in black pots. However, growth was greater when the plants were grown in black pots than in white pots, and yield was similar with either color. Finally, the third experiment was conducted to determine whether shade netting could also be useful for improving soil and other growing conditions for blueberries in the region. Shade netting only affected air temperature at midday and had nearly no effect on soil temperature. The plants had vigorous growth throughout the study, but they were largely unaffected by shade netting. Based on these results, bark mulch and green landscape fabric appear to be the best options for reducing temperatures in the root zone of blueberry in warm climates.

Technical Abstract: The roots of highbush blueberry (Vaccinium sp.) are sensitive to high temperatures and tend to grow poorly in warm soils or warm soilless media. Three experiments were conducted to evaluate strategies for reducing temperatures in the root zone in Evora, Portugal, where soil can reach temperatures > 45 C. The first experiment was conducted in a small planting of ‘Ozarkblue’ blueberry. Treatments included bare soil, a 10-cm-deep layer of aged pine bark mulch, and black, green, and white geotextile landscape fabric. Bark mulch and green landscape fabric resulted in the lowest mid-day soil temperatures among the treatments, which improved canopy development and survival of the plants during establishment. White geotextile fabric also reduced soil temperature but resulted in a considerable amount of weed growth under the fabric. The second experiment was likewise conducted on ‘Ozarkblue’, but, in this case, the plants were grown in 40-L pots filled with a soilless mix of three parts peat, two parts pine bark, and one part humus, by volume. Treatments included black pots and black pots covered with white geotextile landscape fabric. After a year, canopy volume of the plants was greater in black pots than in white pots; however, yield was not affected by pot color. The third experiment was conducted in a 2-year-old planting of ‘Legacy’ blueberry. Treatments included no shade and 60% green shade netting. The netting had no effect on soil temperature in the root zone as a result of the fact that 1) the canopy of plants intercepted the majority of the radiation at midday and 2) frequent irrigation mitigated changes in soil temperature. On the basis of these results, bark mulch and green landscape fabric appear to be the best options for reducing temperatures in the root zone of blueberry in warm climates.