There are many funding sources available for community, schools, nonprofits and others to maintain and plant urban trees. Below is a list of funding sources I am aware of. Please comment below if you know of any other good sources, and I will add them to the list.
State Urban Forestry Coordinators - The best place to start in searching for funding would be to contact your state urban forestry coordinator. They'd be able to point you to other sources in Indiana that might not be available in other states.
Arbor Day Foundation TD Green Streets - They run the Tree City USA program (and have various tree planting programs to help communities. Schools can participate in a similar program, Tree Campus USA, and there are sometimes funds available for campuses as well.
Global ReLeaf- A program run by American Forests, a non profit, to provide reforestation grants to communities.
Alliance For Community Trees- Another nonprofit that facilitates urban forestry grants for communities.
Environmental Protection Agency (US EPA)- their grants for stormwater management and environmental justice have both been used by communities for tree planting/forestry projects. Community development block grants through HUD have been used by communities to purchase trees as well.
Home Depot Community Impact Program - Grants, up to $5,000, are available to registered 501(c)(3) nonprofit organizations and tax-exempt public service agencies in the U.S. that are using the power of volunteers to improve the physical health of their community. Grants are given in the form of The Home Depot gift cards for the purchase of tools, materials, or services.
National Recreation and Park Association - RPA’s Partnership and Business Development department works with funders and like-minded organizations to make an impact through local parks across NRPA’s pillars: conservation, health and wellness, and social equity.
Grants.gov - Learn about and apply for federal funds. This site can be less than user-friendly, but there are a lot of potential opportunities available.