The present study measures the effect of citrate-coated magnetite nanoparticles (Fe3O4-NPs) on the germination and early growth of Quercus macdougallii (oak). Two types of Fe3O4-NPs were synthetized and characterized, being denominated NP1 and NP2. The synthesis was performed by the co-precipitation method and partial reduction of iron(II), respectively. It was found that the NP1 has a quasi-spherical morphology, with sizes of 6–10 nm, while the NP2 has sizes between 65 and 160 nm. It was demonstrated that the Fe3O4-NPs exhibit peroxidase-like catalytic activity. Experiments of germination and growth of Quercus macdougallii were performed using the synthesized Fe3O4-NPs treatments and a deionized water control. The experiments were performed in intact and peeled acorns. The application of the NPs increased the germination up to 33% in relation to the control. Additionally, the Fe3O4-NPs treatments increased the growth, dry biomass, and chlorophyll concentration. The data obtained in this study suggest that Fe3O4-NPs treatments could be potentially used to improve conservation and reforestation of threatened forestry species.