Fort
Use old hay bales to build children a small play fort. Simply stack the used hay bales on top of each other to form walls. Drive a length of rebar through the bales to secure them in place. Place a few extra bales inside of the fort so the children can use them for seating or play tables. The children can use old blankets, sheets and towels to cover the bales and decorate their "furniture." Encourage them to use their imaginations when choosing items to decorate their new fort. If the fort is in a location that receives a lot of sun, drape a tarp over it to provide shade for the children while they play.
Protect Areas from Water Runoff
Build a low wall to protect low-lying areas from water run off or flooding or place them in front of doorways to prevent heavy rains and flood waters from entering a building.
Garden Wall
Stack hay bales to form a wall around your garden to help keep certain animals--such as rabbits and squirrels--from entering. This can also work well with overly curious dogs that like to dig in the garden. Make sure to leave a section open so you can access the garden. To close the garden off, stack extra bales in front of the opening.
Planting and Composting
Dismantle the used bale and spread it over the soil in your garden for an eco-friendly mulch. Till the hay into the soil after the fall harvest, which will add organic material to the soil as it decomposes throughout the winter months. Hay bales can also be used as planters. Cut a hole into the bale and add potting soil and compost to the hole and plant flowers or shallow rooted vegetables. You can grow tomatoes and potatoes in old hay bales without using any soil. The roots weave through the hay and get their nutrients from the decomposing material. The hay keeps the roots insulated and retains the moisture the plants require.
Add hay from old hay bales to your compost pile. Tear the bales apart and mix the hay into the pile so it decomposes quicker.