The increase of the absorption efficiency of boron (B) by plants is essential for increasing crop productivity. The intercalation of B in MgAl layered double hydroxides (LDHs) is an alternative to evaluating how these materials can provide B to plants. In this work, a MgAl LDH intercalated with borate ions (Mg2Al-B-LDH) was synthesized by the constant pH coprecipitation method, and the material produced was evaluated as a matrix for storage and as a source of B for plants. The Mg2Al-B-LDH was characterized by XRD, ATR-FTIR, TGA-DTA, specific surface area, pore size and volume, and SEM. A bioassay was performed to verify the supply of B to plants from the two sources in the forms of H3BO3 and of Mg2Al-B-LDH to sunflower plants grown in pots. The LDH basal spacing value of 12.0 Å is characteristic of intercalation of tetraborate octahydrate ions [B4O5(OH)42−]·8H2O between the layers. There was an increase in the dry matter (DM) and B content of the plants relative to those treatments where no B was added. The lack of statistical difference for plant yield between the two sources of B suggests a lack of stability of the Mg2Al-B-LDH structure under the acidic condition of the soil.