Question
I have weeds and grass growing between my retaining wall bricks and also in planter. What can I use to kill and keep weeds from growing back? Nursery guy recommended KILLZALL or Over-the-Top. I have dismantled part of the wall and will rebuild but want to apply weed and grass killer between bricks.

Answer
Hi John,

To keep the weeds from growing in the wall you will need to apply what are known as non selective residual herbicides.
e.g. Simazine (PathClear).  These chemicals stay active in the area for a few months following application and so prevent weeds coming back.  However these chemicals kill all plants life in the area treated.

If the weeds are growing amongst plants you want to keep you will have to carefully apply a systemic herbicide such as glyphostate (RoundUp)directly onto the weeds being careful not to make contact with wanted plants.

You will need to make 2 or 3 applications of roundup per growing season to give adequate control.

Hope this helps.


Rgds,

Dr Dean Marston.