Southern highbush blueberry ( Vaccinium corymbosum interspecific hybrid) cultivation is a major industry in subtropical regions where low winter temperatures are infrequent and inconsistent. In Florida and other subtropical areas, growers use hydrogen cyanamide (HC) applications during endodormancy to mitigate the negative effects of low chill accumulation. Hydrogen cyanamide is a synthetic plant growth regulator that increases and expediates dormancy release and budbreak. However, southern highbush blueberry cultivars differ in their sensitivity to HC. Optimus and Colossus are two recently released cultivars from the University of Florida blueberry breeding program. The effects of HC in these cultivars are unknown. This research aimed to describe responses to HC applications at different rates for these new varieties. Experiments took place in a commercial farm in Waldo, FL, on 3- to 4-year-old deciduous blueberry bushes. HC was applied at rates of 3.8 g·L ⁻¹ (0.38%), 5.1 g·L ⁻¹ (0.50%), and 6.4 g g·L ⁻¹ (0.63%) in ‘Optimus’ and 3.8 g·L ⁻¹ (0.38%), 5.1 g·L ⁻¹ (0.50%), 6.4 g·L ⁻¹ (0.63%), and 7.7 g·L ⁻¹ (0.75%) in ‘Colossus’. In both cultivars, the control treatment was not sprayed. Vegetative bud count, and flower bud development, flower bud mortality, and yield were determined. HC application thinned reproductive buds and increased vegetative budbreak. Although seasonal yield was not increased, HC advanced fruit ripening early in the season.

Blueberry plants (Vaccinium corymbosum interspecific hybrids) need soils with acidic pH and high organic matter. This leads growers to use soil amendments like pine bark and soil acidifying agents like sulfur. These inputs raise agricultural production costs and compromise the economic sustainability of blueberry production. Sparkleberry (Vaccinium arboreum) seedlings have been utilized experimentally as rootstocks for blueberry in Florida, but the impact of clonal sparkleberry rootstocks on blueberry productivity and quality is unknown. The objective of this study is to evaluate the performance of southern highbush blueberry (SHB) cv. 'Patrecia' grafted onto three clonal sparkleberry rootstocks. Based on previous research, we hypothesized that grafted blueberries have higher yield and fruit quality than own-rooted blueberries in minimally amended soil. 'Patrecia' SHB was grafted onto three different clonal rootstocks (R1, R2, and R3). Plants with their own roots were used as a control. Fruits were harvested in the springs 2019, 2021 and 2022. For each harvest season, fruit yield and quality (average fruit size, total soluble solids, titratable acidity, and firmness) were measured. Grafted plants exhibited equal or higher yields than own-rooted plants in 2021 and 2022. Grafted plants produced larger berries, and the quality of the fruit was similar among treatments. These results suggest that clonal sparkleberry rootstocks can be used to grow blueberries in soils with higher pH and less pine bark than is currently used.

Humic acids are a biostimulant that has captured the interest of blueberry growers, but information about humic acid use in blueberry is scarce. Blueberry plants suffer water deficit stress during transplant and photosynthetic limitations during fruit development. We hypothesized that humic acid applications improve transplant success and increase fruit yield and quality in southern highbush blueberry (SHB, Vaccinium corymbosum interspecific hybrids) grown in soilless substrates. We tested these hypotheses in two greenhouse experiments. First, we grew 'Sweetcrisp' SHB in rhizoboxes. Humic acids were applied via drench at concentrations of 0 mL⋅L − 1 , 7 mL⋅L − 1 , 13 mL⋅L − 1 , and 24 mL⋅L − 1 for 10 weeks. Humic acid application increased substrate respiration rates, pH, and electrical conductivity, but they did not increase root growth or improved transplant success. In a separate experiment, one year-old plants of 'Avanti', FL 09-311, and FL 06-19 SHB plants in 1.7 L pots were treated with 0 mL⋅L − 1 , 13 mL⋅L − 1 , and 24 mL⋅L − 1 humic acids during the fruit development period. Humic acid application did not increase yields and occasionally reduced fruit quality. While plant responses were genotype specific, these results suggest that humic acid applications are not beneficial during the transplant or fruit development periods in substrate-grown blueberry.

Blueberry (Vacciniumcorymbosum interspecific hybrids) production in soilless substrates is becoming increasingly popular. Soilless substrates have low pH buffering capacity. Blueberry plants preferentially take up ammonium, which acidifies the rhizosphere. Consequently, soilless substrates where blueberry plants are grown exhibit a tendency to get acidified over time. Agricultural lime (CaCO3) is commonly used to raise soil and substrate pH in other crops, but it is rarely used in blueberry cultivation. We hypothesized that substrate amendment with low rates of agricultural lime increases substrate pH buffering capacity and provides nutritional cations that can benefit blueberry plants. We tested this hypothesis in a greenhouse experiment with ‘Emerald’ southern highbush blueberry plants grown in rhizoboxes filled with a 3:1 mix of coconut coir and perlite. We found that substrate amendment with CaCO3 did not cause high pH stress. This amendment maintained substrate pH between 5.5 and 6.5 and provided Ca and Mg for plant uptake. When blueberry plants were grown in CaCO3-amended substrate and fertigated with low pH nutrient solution (pH 4.5), they exhibited greater biomass accumulation than plants grown in unamended substrates. These results suggest that low rates of CaCO3 could be useful for blueberry cultivation in soilless substrates.

Rhododendrons (Rhododendron spp.) are ornamental plants in the family Ericaceae that thrive in acidic soils and are challenged by neutral or alkaline soils. This soil requirement limits the locations where rhododendrons can be grown and causes chlorosis, diminished growth, and low survival when rhododendrons are grown in high pH soils. While growth and survival impacts are widely documented, little is known about how high pH soils cause these symptoms in rhododendrons. We hypothesized that high pH stress impacts root form and function, leading to nutrient deficiencies that limit plant growth. We tested this hypothesis in a hydroponic experiment. “Mardi Gras” rhododendron liners were grown in a complete nutrient solution at pH 5.5 (optimum pH) or pH 6.5 (high pH) for 49 days. Biomass accumulation, nutrient uptake and concentration, and root stress were assessed. High pH nutrient solutions diminished leaf and root growth. Plants grown in high pH nutrient solutions developed clusters of short, highly branched roots. Plants grown in optimum pH did not exhibit this morphology. High pH affected the uptake and translocation of most essential nutrients. S and Mn deficiencies likely limited plant growth. High pH had a nuanced effect on root oxidative status. These results suggest that rhododendron root morphology and nutrient uptake are directly affected by high pH and that aboveground symptoms might be a consequence of impaired root function.