Many growers are using biostimulants such as humic substances and natural extracts from seaweed in an effort to improve plant growth and production in their crops. These products are used typically as foliar sprays or soil supplements and often work best when applied with fertilizers. Initially, we discovered that application of humic substances (humic and fulvic acids) increased plant growth during the first 2 years after planting in 'Draper' northern highbush blueberry (Vaccinium corymbosum L.). The effects of the humic substances on root growth were particularly apparent and resulted in 49-52% more dry root biomass than either conventional fertigation or a control treatment that lacked humic substances but contained exactly the same nutrients as the treatment with humic substances. We then conducted a trial in a mature planting of 'Bluecrop' northern highbush blueberry. In this case, humic substances increased root growth and the availability of P and Zn in the soil relative to controls with fertilizer only, but after 3 years, they had no effect on shoot growth, yield, or fruit quality. Next, we tested several biostimulants, including humic substances, extracts from Ascophyllum seaweed, and a mix of N-fixing bacteria (Azorhizobium caulinodans, Azoarcus indigens, and Azospirillium brasiliense), on potted plants of 'Draper' blueberry. Fertigating with humic substances or seaweed extract increased growth of the plants relative to using the bacterial mix or nutrients only; however, the response was quite different between the two products. Plants grown with humic substances were greener and contained more N than those in the other treatments, while those grown with seaweed extract tended to be taller and more upright. Clearly, the use of these products can be beneficial during establishment of highbush blueberry, but more research is needed to determine exactly how they work and whether they are useful under all circumstances.