Phosphorus (P) is an essential nutrient for the growth and development of southern highbush blueberry plants (SHB, Vaccinium corymbosum interspecific hybrids). SHB plants exhibit both morphological and physiological responses to P deficiency. Previous studies have shown that P-deficient SHB plants shift their biomass allocation strategy—favoring root growth while limiting canopy development. Although this response may be detrimental in fruiting fields, it could be advantageous in nursery settings, where young plants must rapidly establish roots in new soils or substrates. Here, we report the results of an experiment evaluating the response of two SHB cultivars, ‘Farthing’ and ‘Sentinel’, to five different P fertilization rates during the nursery stage. Rooted cuttings were transplanted into 1.0-L pots filled with a substrate consisting of 70% coconut coir and 30% horticultural-grade perlite. Plants received weekly applications of 0, 15, 30, 45, or 60 mg P, while all other nutrients were supplied through a P-free commercial fertilizer. The plants were grown in a temperature-controlled greenhouse for 12 weeks. Subsets from all treatments (n = 6) were destructively harvested at weeks 0, 4, 8, and 12 to assess plant growth and nutrient content. P fertilization treatments had profound effects above and belowground. Leaf P concentrations exceeded the deficiency threshold only in plants receiving more than 15 mg P per week. Root biomass responses to P treatments differed between cultivars: low P rates increased root biomass in ‘Farthing’ SHB but decreased it in ‘Sentinel’ SHB. P deficiency symptoms appeared in ‘Farthing’ SHB leaves after 12 weeks, while symptoms appeared in week 8 in ‘Sentinel’ SHB leaves. These findings suggest that a brief period of suboptimal P fertilization could be used to promote rooting in ‘Farthing’ SHB during nursery production. However, this strategy may not be effective for ‘Sentinel’. Future research should explore P deficiency responses across a broader range of SHB cultivars to develop generalizable nursery practices that encourage rapid root development while minimizing P leaching.
