Physically removing a bush's roots can be hard work. But most commercial root killer chemicals can leave residue in the soil for years, and anything subsequently planted in the soil is likely to suffer. Homemade root killers are your best option to remove a bush's roots. However, keep in mind that even commercial chemicals can take a year or more to work. If you are in a hurry to re-plant the area, consider removing the roots by hand or hiring someone to do it for you.
Cut back the bush's foliage as close to the ground as possible if you have not done this already. Smaller bushes can be pruned back with lopping shears. Large bushes with thick branches will need to be felled with an axe or chainsaw.
Use a drill with a large bit to drill holes in any remaining surface wood, any visible roots and at various spots round the root system.
Fill the drilled holes with salt.
Pour boiling water into the holes and all over the root area.
Pour undiluted bleach into the holes and all around the roots the following day.
Repeat steps 3 through 5 once weekly for one month.