Throughout the world, deforestation continues at an alarming rate of about 13 million hectares a year. Human activities are by far the most common and most destructive cause of deforestation in Africa and other tropical regions. On-farm tree planting has therefore been promoted for decades as an intervention to ease local community dependence on forest resources in Kenya with little success. There is also a dearth of information on the main factors that influence adoption of on-farm tree planting. Most rural people depend on forests for firewood, timber, and other products, hence the need for adoption of on-farm tree planting to ensure sufficient supply and reduce dependence on forests. This has not been achieved due to the scarcity of resources as a result of the high poverty rates in the area. This study therefore sought to determine the factors that influence adoption of on-farm tree planting premised on the fact that farmers allocate land to on-farm tree planting based on the household subsistence needs and surplus to earn income for the household. The study population of 13,411 households consisted of farming households from Shinyalu Sub-county. Simple random sampling was used to select a sample size of 384 respondents from households. Primary quantitative and qualitative data was collected using semi-structured questionnaires, key informant interview guides and focus group discussion guides. Quantitative data was analyzed using descriptive statistics, frequencies and cross tabulation analysis. Qualitative data was analyzed using content analysis. Data was analyzed and interpreted using descriptive statistics, frequencies and cross tabulation analysis. The findings of the study showed that the main factors influencing adoption of on-farm tree planting were; land size, family size, education level and distance from the home to the forest. The land sizes were very small with majority of the respondents having less than 2 acres. With the small land sizes of less than 2 acres and large families of over 10 members, they opted to plant food crops and rear livestock for milk production in order to feed their families. Ancestral accession is also a major contributor to the low adoption of the practice since land has to be sub-divided many times to all the male children in the home. Households with more than 10 members planted fewer trees while those with few family members planted more trees. The most educated people planted more trees while the least educated planted fewer trees. Households closer to the forest planted fewer trees while those far from the forest planted more trees. This study recommends that sensitization and training of farmers should be done on the importance of on-farm tree planting, propagation of seedlings, and nursery management practices for sustained production and continued planting of trees on farms.