The development of plant‐specific biosensors holds the potential to uncover new insights into plant physiology and advance precision agriculture. Current sensing platforms mainly focus on broad plant phenotypes (e.g., elongation and hydration) and local environmental monitoring (e.g., temperature and moisture). Here, an ion‐selective organic electrochemical transistor (IS‐OECT) is introduced that enables real‐time monitoring of variations in potassium ion concentration within the xylem of pine trees. This work demonstrates that the high sensitivity of the IS‐OECT enables the detection of subtle variations in potassium ion concentrations in the xylem sap of living trees, and the high stability of the sensor allows for in vivo measurements over five weeks. Furthermore, the implantable sensors are fabricated using processes that are compatible with low‐cost manufacturing (i.e., lithography‐free). This sensing technology, therefore, has great potential to be a game‐changer in precision forestry and could extend to precision agriculture and horticulture practices.

Natural Rubber Latex (NRL) obtained from Hevea brasiliensis is a biocompatible electrically insulating material with exceptional mechanical properties. Poly(3,4-ethylene dioxythiophene) poly(styrene sulfonate), PEDOT:PSS, on the other hand, is a biocompatible highly conductive organic material with poor flexibility. We hereby introduce a blend of NRL/PEDOT:PSS (N/P). This study involved different N/P volume ratios and temperatures of curing aiming at an optimal combination of good flexibility and conductivity. Low-temperature annealing, at 60 °C, dries and cures the blend in a few minutes and improves its tensile strength and conductivity. The blend can stretch more than 700% of its initial length and presents a good gauge factor and small resistance variation (R/R₀) for ΔL/L₀ of up to 100%. Among the different N/P concentrations, the membranes of an N/P ratio of 1/4 and those thermally cured have the most promising conductive flexible properties for bioelectronic applications.