Intercropping arable crops between tree rows has proven to be a great alternative to conventional agriculture in terms of food production sustainability and climate change adaptation. However, close interactions between species in these systems sometimes yield adverse allelopathic effects. In this study, the possibility of intercropping barley and maize in the walnut orchard was investigated in terms of walnut leaf litter toxicity. Leaves from 15 and 30 years old walnut trees were used to prepare water extracts out of freshly fallen leaves and soil with leaves decomposed within. Barley and maize seeds were germinated in these extracts using between paper towels method. Fresh leaf litter extracts slightly reduced barley germination but significantly inhibited both barley and maize seedlings’ growth. The extract from older walnut tree leaves had the most severe toxic effect, and seedlings shoot was more sensitive than root for both species. A significant correlation was observed between extracts pH and seedlings lengths, suggesting the hydrogen-induced injury to the root, which consequently influenced growth. Decomposed leaf litter extract had a promotional effect on barley and maize germination and growth, which shows that appropriate walnut litter management could improve the performance of intercropped walnut systems.