Under the conditions of the least inputs such as no-chemical fertilizer, no-chemical insecticide, and no-weeding, this experiment was carried out to examine the effect of mixed-seeding date on growth of hairy vetch and radish, and on the status of weed occurrence. Radish was severely damaged by insects during the whole growth period. Many summer annual weeds emerged and grew vigorously when the seeding date was August 14, but rarely emerged when the seeding date was August 28. Most growth parameters of hairy vetch and radish were higher when the seeding date was August 14, compared to those of the seeding dates of August 21 and August 28. For the mixed seeding of hairy vetch and radish under the conditions of the least inputs, the seeding date during the middle of August could be recommended.