- As blueberry (Vaccinium sp.) production has increased in recent decades, a new interest has developed in the cultivation of blueberry in soilless substrate containers. Historically, blueberry has been propagated and grown in soilless substrate at nurseries, but nursery production is short in duration and plants are small relative to a mature blueberry. There is little literature on the subject of substrate blueberry production, and because blueberry is a long-term perennial that prefers soil pH in the range of 4.5-5.5, it is likely requirements are different than most other small fruit crops grown in soilless substrate for fruit production. Three studies were conducted in Corvallis, OR with container grown northern (V. corymbosum L.) and southern highbush blueberry (interspecific hybrids of V. corymbosum L. and V. darrowii Camp.) to investigate how media and fertilizer composition influence growth and nutrient uptake.In two studies we investigated the effects of various substrate ingredients on blueberry growth and nutrition in a greenhouse for 3-4 months. The first study evaluated cultivar ‘Snowchaser’ in eleven unique treatments, 10 from combining sphagnum peat moss,coconut coir (Cocos nucifera L.), and douglas fir bark [Pseudostuga menzii Mirb. (Franco)] with 10% perlite by volume and one commercially available mix. The second study evaluated 16 different mixtures of peat moss, coir, and perlite on one northern highbush cultivar (‘Liberty’) and one southern highbush (‘Jewel’). Treatments in the second study consisted of four levels of perlite (0, 10, 20, and 30% by volume) and four ratios of peat:coir (1:0, 2:1, 1:2, and 0:1). All plants in both studies were fertigated with a complete nutrient solution suitable for blueberry and target leachate drainage was 25%. Every 2 weeks, leachate was collected from treatments and analyzed for pH and electrical conductivity (EC). Plants were destructively harvested and dry weight and nutrient content were measured. In the first study, total dry weight of the plants was similar among the treatments at 72 d after transplanting but was nearly twice as much, on average, in the commercial mix, and media with ≥ 60% peat or coir than in those with ≥ 60% bark at 128 d. Bark had lower porosity and water holding capacity than peat, coir, or the commercial mix. Increasing bark in the medium also reduced nutrient uptake efficiency of N, P, K, S, Ca, Mg, Fe, Mn, B, Cu, and Zn relative to peat or coir. The effects of bark on nutrient uptake efficiency were largely driven by differences in dry weight. In the second study, increasing the amount of perlite in the media decreased dry weight in ‘Jewel’ and had no effect on dry weight in ‘Liberty’. When media contained perlite, the proportion of peat and coir in the media had no effect on dry weight of either cultivar, supporting the results of the first study. When no perlite was in the media, increasing the amount of peat (decreasing coir) in the media increased dry weight in ‘Liberty’. Increasing peat (decreasing coir) in the media improved nutrient uptake efficiency for P, K, Mg and Zn for both cultivars, and N, Ca, S, and B in ‘Liberty’. Inaddition, increasing the amount of peat in the media increased whole-plant concentration of P and Mg in ‘Jewel’ and N, P, K, and B in ‘Liberty’. The amount of perlite in the media had no effect on leachate pH. In both studies leachate pH was lowest for peat-containing mixes and highest for coir mixes; however, pH was similar in all mixes by the end of the studies. Results from our two media studies indicate that high levels of perlite or bark in the media can negatively impact initial growth of young blueberry plants through their influence on media water holding capacity. Initial growth of young blueberry plants is similar in media containing peat or coir; however nutritional differences between the two media components may necessitate differences in nutrient management.The third study evaluated the effects of K fertilizer source and rate, in combination with two N sources on shoot growth, fruit yield, fruit size and fruit firmness of ‘Liberty’ blueberry from 2015 to 2016. Plants were grown in 25 L containers with a substrate mixture of 3 sphagnum peat: 1 coir : 1 perlite. The three K sources used were potassium sulfate (KS), potassium thiosulfate (KTS), and potassium acetate (KA) at rates of 0, 50, and 150 ppm K in ammonium sulfate and urea. Additionally, KTS and KS were applied at 100 and 200 ppm K in ammonium sulfate. Every two weeks leachate from pots was collected and analyzed for pH and EC. During the second growing season fruit yield, quality (size and firmness), and nutrient content, and shoot growth (dry weight) and leaf nutrient concentrations were determined. When the plants were fertilized with ammonium sulfate, shoot dry weight increased with a moderate rate (50 ppm K) of KS or KA (396 and 370 g dry wt. per plant, respectively) versus the 0 ppm K control (269 g dry wt. per plant ), but there was no effect of K fertilization on fruit yield or quality. Whenplants were fertilized with urea, K fertilizer had no influence on shoot growth, yield, or fruit quality. Increasing concentration of K in fertilizer increased leaf K concentrations and decreased leaf Ca and Mg concentrations in both N fertilizers. Increasing fertilizer K also increased fruit K concentration in urea but not in ammonium sulfate. Leaf and fruit S concentrations were enhanced by the addition of KTS (X̅ = 0.3% and 0.10%, respectively) but not KS (X̅ = 0.2% and 0.09%, respectively). Both KTS and KS reduced leachate pH (X̅ = 4.58 and 5.01, respectively) relative to no K (X̅ = 5.44), whereas KA had no effect on leachate pH. Fertilizing substrate grown blueberry with K can have positive benefits on early growth and nutrition provided the appropriate K source and rate and N source are used.