Control weeds growing outside the greenhouse to prevent seed from blowing into the house. Remove weeds from the house before they have a chance to flower. Media can be steam sterilized to help with weed control, although some weed seed will not be killed. Maintain the media at 180 F for at least 30 minutes when steam sterilizing potting mix. There are very few herbicides that can be used in greenhouses.
Greenhouses can trap herbicide vapors around plant foliage, which can lead to injury.
For example, trifluralin, which is widely used in ornamentals and other crops maintained outside, cannot be used in a greenhouse due to the volatility of the compound. Compounds such as 2,4-D can cause severe injury if applied in a greenhouse. No preemergence herbicide is currently labeled for use in greenhouses. The restrictions in the Surflan label limit the situations where this product could be used. Read and follow all label restrictions for these products.