Better known as hay bale gardening you have a choice of the type of hay bale you wish to use.
Start with a bale of lucucen or barley, or even peanut bales. Pine straw won't work.
Bales that have been sitting out in the weather will give you a far better start, because they need to rot before you plant.
Fresh bales will requires a pretreatment. Place the bales in full sun where they can stay all summer, because once they start to rot, they're not very mobile.
Don't remove the baling twine you don't want the bales to fall apart.
I've found that a metal stake [star picket] at both ends will help hold twine bound bales together when the twine rots.
The bale should be ready for planting when you notice the material starting to decompose.
Mix topsoil and rotted cow manure for a 50-50 mix. Put about 100 mm of this mixture on top of each bale and moisten it lightly with a fine water spray to wash the mixture into the bale.
Transplant your seedlings right into the bale. Use your hand to pull apart the bale and insert their roots. Dont over crowd your bale and dont planr tall growing vegetables into the bale as it will fall over.