Cutting down some invasive or aggressive shrubs and bushes isn't enough to kill the entire plant. Many species will regrow from the stump or from extensive underground root systems. To get rid of these pests, you'll need to kill the underground part of the plant as well as the above-ground portion. You can do this using a number of common, inexpensive household materials, but it's important to take some precautions.
The simplest way to kill a stump and its attached root system is to cover the surface in a layer of moist, fertile soil such as potting mix or topsoil. The high nitrogen content of these materials encourages organisms that break down the wood and speeds up decay. Pile the soil several inches deep to keep the stump from being uncovered by wind or rain, and make sure the heap stays moist for best results. This technique works best with less-vigorous bushes. Some very aggressive species will continue to grow under the soil.
Pouring boiling water on a stump can kill off growth cells and encourage fungi and bacterial colonies. Saturate the freshly-cut stump thoroughly, but try to keep the water away from nearby vegetation. Unlike soil mounding, hot water can kill desirable plants as well as pest roots.
Mineral salts produce a drying effect on plant tissues, pulling water out of living cells and slowly killing them. You can use ordinary rock, table or Epsom salts to kill the root system of an undesirable bush. Simply drill holes in the surface and sides of a freshly-cut stump, then stuff them with salt. Do not simply pour salt on the stump or the surrounding area, since it can irrevocably damage the soil and kill nearby plants.
Applying sugar to the stump of an undesirable bush can speed up decay and reduce the risk of resprouting from the roots. Sugar adds carbon to the wood, providing food for beneficial organisms and eventually killing the roots. Drill a series of one-inch holes in the top and side of the stump and pack them with ordinary granulated sugar. This method works best after the bush has been allowed to decay for at least a few months.
Slow-release fertilizers with a high nitrogen content work well to kill the stumps and roots of unwanted bushes. While they accelerate growth in intact plants, they speed up the early part of the decay process when injected or placed in holes drilled into a stump. Fertilizer can also be used directly on an intact stump, but this method increases the risk of run-off and fertilizer burn in surrounding plants.
Homemade root and stump killers may not be sufficient to kill extremely aggressive pest shrubs and bushes. If you experience regrowth from a bush you have already cut down, trim off the new shoots and paint all exposed wood with a commercial herbicide like triclopyr or glyphosate.
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