Nitrogen concentrations were significantly higher in walnut leaves from trees planted with autumn‐olive than in leaves from walnut planted alone, while the reverse was true for potassium. The amount of nitrogen, phosphorus, potassium, calcium, and magnesium based on leaf weight was higher in leaves from walnut trees mixed with autumn‐olive than in leaves from walnut planted alone. The differences in nutrient content between the mixture and walnut alone increased over the sampling period as leaf weights increased proportionately more in the mixture. The increased mobilization of minerals into the leaf is attributed to the increased availability of nitrogen fixed by autumn‐olive and the subsequent uptake by walnut in the mixture. The better nutrition of trees in the mixture compared to walnut planted alone has resulted in better growth and a longer growth period.