Pre Emergent and Post Emergent Herbicides:

What Are The Differences?

Pre-Emergent Herbicides. Pre-emergent herbicides should be applied in the early spring season just as the ground temperature is beginning to rise. This is because these weed killers take their action before the plants’ seeds germinate and start to grow underground. Pre-emergent herbicides work by creating a protective seal around the seeds to prevent germination. Essentially, these herbicides suffocate the plants and eliminate any chance of growth. Pre-emergent herbicide can be applied in either liquid or granular form. The soil will readily absorb both forms; however, you must also add water to the soil if you choose to use a granular pre-emergent herbicide.



Extensive Lawn care is essential for healthy grass.

Because water is needed to activate herbicide granules, either a spring rainfall or a watering with a sprinkler will trigger the effects of the spread granules. Weeds like crabgrass that annually sprout from new seeds are treated best with pre-emergent herbicide. On the other hand, this type of weed killer does not have an effect on perennial weeds that sprout up each year from deep root systems. Because pre-emergent herbicide takes action on seeds, it has no way to treat perennial weeds with deep, extensive roots.


Post-Emergent Herbicides. It is for these perennial weeds that post-emergent herbicides come into play. Post-emergent herbicides can be applied to plants once spring has begun and plants have started to grow after seed germination. This is because post-emergent herbicides attack weeds in a much different manner from the germination prevention of pre-emergent herbicides. Post-emergent weed killers travel down the stalk of the plant and into the root system, killing weeds after they’ve already started growth above the ground. Like pre-emergent types, post-emergent herbicides can be used in either liquid or granular form. If using the liquid form, apply the herbicide spray directly to the weeds you are looking to eliminate. If you use the granular form, be sure to activate the herbicide with water after spreading the granules over the key area. Most post-emergent herbicides need to be applied multiple times throughout the growing season, and then a thorough final application in late fall will help to prevent new weed growth in spring.

Follow Green Dreams Landscaping on Twitter