I want to kill some grass growing near my roses. I was told that Roundup works well and I could plant in the soil the next day. Is this true?

Glyphosate, the herbicide in Roundup, will kill many weeds including most grasses, but you should be very careful if you use it near roses. The herbicide is not selective and can damage or kill roses and other desirable plants if it is sprayed on them. Glyphosate is systemic and is absorbed by green foliage and green bark.  Even dormant roses can absorb the herbicide if they are sprayed. Once the herbicide is absorbed by a plant it can remain in the tissue for several months. Glyphosate is transported to growing parts of the plant both above and below ground.  It keeps the plant from producing certain amino acids which are necessary for growth. The foliage of treated plants will turn yellow, wilt and die.

Glyphosate is not usually absorbed by plant roots; the herbicide is held very tightly on clay particles in the soil and is eventually broken down by microorganisms. If you use Roundup Weed and Grass Killer or Roundup Weed and Grass Killer Plus, you should be able to safely replant an area that was sprayed within a few days.  Do not use Roundup Extended Control Weed and Grass Killer if you wish to replant in treated soil.  This product contains a pre-emergent herbicide that prevents seed from sprouting and it may inhibit root growth on new transplants.

By V. Lazaneo, Urban Horticulture Advisor, Emeritus, UC Cooperative Extension, August 2012