Standard Roundup is a post-emergent herbicide, not a pre-emergent. This means it won’t kill seeds before they break the soil surface. Instead, Roundup attacks plants after they have matured. Some specialized Roundup products work as both post-emergent and pre-emergent herbicides, since they stop new growth for up to 12 months. However, these sprays will kill all plants and grasses, so they are not suitable for use in lawns. Instead, use a pre-emergent herbicide that will stop weeds from sprouting but won’t kill your established lawn grass.
Does Roundup Prevent Germination?
Spraying standard Roundup on weeds won’t do anything to prevent future seeds from germinating. Glyphosate—the main chemical in Roundup—attacks an enzyme that can only be found in fully-grown plants, not in seeds. Any glyphosate that is not absorbed by plants will break down prior to moving into the soil. This makes most Roundup products great for killing plants that have already sprouted but leaves them useless for stopping seeds from germinating.
- Standard Roundup does not prevent weed germination.
- The glyphosate in Roundup breaks down prior to entering the soil.
- This Roundup spray will kill plants and stop seeds from sprouting for up to one year.
If you want to use Roundup to stop weeds from sprouting, use a long-lasting Roundup spray. These sprays will kill all growing plants in an area with glyphosate. Then, a pre-emergent herbicide remains in the soil for up to one year, preventing all future growth. Weed-preventing Roundup is best used to stop weeds from growing through gravel or paved areas. Roundup Max Control 365 is a bad choice for your lawn because it will kill all the grass in the area, along with the weeds. Then, nothing will grow in the dead spot for up to twelve months.
How is Pre-Emergent Herbicide Different from Roundup?
Pre-emergent herbicides are designed to prevent seeds from sprouting in the first place, but they won’t kill your established grass or garden plants. In comparison, Roundup sprays attack all actively growing plants, including grasses. So, using a pre-emergent allows your lawn to thrive by preventing invasive plants from sprouting. Using any form of Roundup on your lawn will kill your grass.
- Pre-emergent herbicides will stop weed germination from happening, but will NOT kill existing plants and grasses.
- Standard Roundup will kill all mature plants and grasses but will NOT stop seed germination.
- Long-lasting Roundup products will kill all plants and grasses AND prevent any new growth for up to one year.
Because Roundup attacks all actively growing plants and grasses, it is classified as a “non-selective herbicide.” Use extreme caution when spraying Roundup near plants and grasses you do not wish to kill. Shield desirable plants from Roundup overspray by using cardboard or wood sheets. If you cannot spray Roundup on weeds without also spraying desirable plants, consider using a different weed-killing method.
When to Use Roundup vs. Pre-Emergent
Use standard Roundup to kill all the plants and grasses in an area where you plan to plant again soon. This makes standard Roundup useful for killing a lawn full of weeds so you can start over with new sod. Alternatively, you can use standard Roundup to wipe out all plants in a weed-infested garden patch. In two weeks, it will be safe to plant again.
Long-lasting Roundup products are great for killing all the plants in an area and keeping all plant growth out for up to a year. Spray long-lasting Roundup under decks, in gravel areas, and in driveway cracks. This will create a “no plant zone” where no grasses or weeds will grow. Any seeds or plants that attempt to grow here will die.
- Use standard Roundup to kill all plants and grasses in an area that needs replanting.
- Spray long-lasting Roundup where you want to kill all plants AND prevent any new growth in the area.
- This pre-emergent is used to stop new seeds from sprouting without harming your existing plants. It is great for established lawns and gardens.
Use pre-emergent when you want to stop any new plants from sprouting in your lawn, but you want your grass to remain unharmed. The best way to prevent weeds in grass is to apply pre-emergent at the right time. This way, your existing grass can thrive but no weeds will invade. You can even spread pre-emergent in flower beds to stop weed seeds from sprouting there.
Can You Apply Pre-Emergent and Roundup at the Same Time?
It is not recommended to use a pre-emergent and post-emergent, like Roundup, at the same time. Pre-emergents only work on seeds before they grow, and post-emergents kill weeds after they grow. If you currently have a lawn full of weeds, pre-emergents won’t do anything, but Roundup is a good option. Additionally, pre-emergents need to be watered in, but hosing weeds with water right after using Roundup can wash the product away. Applying both herbicides at the same time is ineffective, labor-intensive, and costly.
- Don’t use Roundup and a pre-emergent herbicide at the same time.
- Unlike pre-emergents, Roundup can kill full-grown weeds at the time of use.
- Pre-emergent applications need to be timed correctly, when post-emergents aren’t in use.
Always apply your pre-emergent in the early spring and/or fall, before annual weeds have a chance to grow. Roundup can then be used to kill weeds along fence lines, driveways, and sidewalks. Always be mindful of your desirable plants because Roundup is non-selective, which means it will kill any green plant it touches.
Can You Use Roundup as Pre-Emergent?
Before you attempt to use Roundup as a pre-emergent weed control, review these facts:
- Standard Roundup spray has no pre-emergent properties.
- Specialized Roundup products do have pre-emergent properties, but they will kill all mature plants too.
- All Roundup products attack all actively growing plants and grasses.
- Specialized pre-emergent herbicides stop seeds from sprouting but won’t harm mature plants.
Roundup products are not a suitable replacement for pre-emergent herbicides because Roundup attacks every plant it comes in contact with. Because Roundup cannot be safely used on grass—unlike other herbicides—you should only spray it on or near plants you wish to kill.