Pre-Emergent Herbicide vs Post Emergent Herbicide Pre-Emergent Herbicide vs Post Emergent Herbicide

When embarking on weed prevention, there are two primary types of weed killers, pre-emergent herbicides and post-emergent herbicides. Knowing the differences between these two types of weed killers and how to correctly use them during the year will make a huge difference in how effective your weed killing pursuits will be during the growing season.

Pre-Emergent Herbicides

This type of weed killer is used early in the spring, before plants really begin to grow and the weather turns warm. A pre-emergent herbicide creates a protective barrier seal around seeds, which prevents the seed from germinating and growing. In essence, the seed is suffocated and dies.

Pre-emergent herbicides are used early in the growing season. They are best applied when the temperature is lower than 60 degrees and the soil is just beginning to warm.

You can apply the herbicide to the soil either by spraying it in liquid form or by spreading it in granular form. The soil will absorb both forms. Water activates the granules. Either a spring rainfall or watering with a sprinkler system after the granules have been spread will be an effective way to activate the granules.

Pre-emergent herbicides are only effective on weeds, like crabgrass, that annually sprout from new seeds. These herbicides do not effectively treat perennial plants like established quack grass because they have a deep root system and simply reemerge every year as the weather warms.

Post-Emergent Herbicides

The other type of weed killer is a post-emergent herbicide. This type of weed killer is used once the initial spring season has begun and plants have started to grow. Once a plant has started to grow it is too late to utilize the germination prevention of a pre-emergent herbicide and it is time for you to apply a post-emergent herbicide.


Post-emergent herbicides work by traveling down the plant stalk and into the root system. If you are using the liquid form of the herbicide, apply it directly to the weeds. It is better to apply the spray after the base of the plant has been cut or torn away because the plant structure will be open and the herbicide will go directly into the plant system.

If you are using the granular form, apply the herbicide to the lawn with a spreader and then activate it with the lawn sprinklers.

Post-emergent herbicides usually need to be applied several times throughout the growing season. Often, a thorough final application during late fall will help prevent new weeds from growing in the spring and prevent weeds from spreading seeds.

It is important to understand the difference between specific and non-specific herbicides. Specific herbicides are most commonly used for lawn care and other weed elimination efforts by homeowners. They specifically target weeds and do not usually harm other surrounding or adjacent plants. A non-specific herbicides, on the other hand, will kill all plants it comes into contact with. It is most commonly used by landscapers or developers who are clearing a lot or area for a new building or for landscaping purposes.

Got a New Project You're Proud of?

Post it on Your Projects!