Outdoors

[krava2]

How long should I wait before I can safely plant plants in an area where weed killer was used?  I was told 30 days, but when I looked at some of the products on line is looked like four months.

Thank you to all who answer.

[Ingar_HD_ATL]

Hey krava2.

It would depend which weed killer you put down, as to how long until you can plant.

SELECTIVE HERBICIDES

There are selective herbicides like Ortho's Weed B Gon or Spectracide's Weed Stop and many others that use the active ingredient 2,4-d. This product is absorbed through the stoma's of the leaves, which is how it kills the plant. It is not absorbed through the roots, therefore once it touches the ground it is pretty much safe to plant plants. Planting seed on the other hand will require you to wait 1 month after an application of 2,4-d. As a precaution I still tell people to wait 5 to 7 days to plant plants.

NON-SELECTIVE HERBICIDES

Non selective herbicides like Round Up or Spectracide Weed and Grass Killer, use an active ingredient called Glysophate. This highly effective herbicide kills the same way as 2,4-d, by being absorbed through the leaves and not through the roots, however it is used by the U.S. Parks and Recreation Dept because of its short residual effects in the ground. You are safe to plant plants 4 or 5 days after application and safe to seed a week after an application of Glysophate.

Some selective herbicides like the Round Up Extended control have a pre-emergent in them which will prevent you from overseeding for up to 4 months but should not really effect your time for planting plants, as pre-emergent only prevents seed germination.

Do you remember which weed killer it was? Hit me back here on the community and I can give you more specifics.

[krava2]

I have not used the weed killer yet. I am doing research so that I can purchase the correct one for my situation. I need one that will kill the roots as I have already cut-down and pulled out as much as I can. The roots look like carrots and can be very large and deep. I have even used a shovel to dig some of them out. Whatever this weed is, it does tend to vine and climb up my trellis but not the side of the house. I plan to move a 6 foot plus tall porter weed plant into this area after the frost threat has left, probably March or April. I want to be sure that whatever I use will not damage the porter weed plant or cause harm to the butterflies and caterpillars and the milkweed and porter weed plants are attracting the butterflies and humming birds.
Thank you very much for your help.

[Ingar_HD_ATL]

Hey krava2.

You will need leaves on the plants that you want to kill because weed killers that are safe to the soil will only kill things when absorbed through its leaves. The weed killers that will kill the plant through the soil will also contaminate the soil for long periods of time.

You can spray Round Up on these weeds when the leaves grow back on the weeds and once temperatures are warm enough. It will be safe to plant your desirables the next week, as Round Up is neutralized once it touches the soil.

Round up is an herbicide, not a insecticide, so it will not harm your insects. State parks use Round Up because it works so well and is relatively safe for the environment by having very little residual effects.

Once you plant your plants, be sure to put your mulch down thick, as this will help prevent weeds from coming up in your flower beds.

[tachikara]

Hi, Green Giant,

I got my backyard done this past summer.  It used to be full of weeds, but the weeds were treated/removed and sod was laid down.

I'm starting to see weeds pop up in my new lawn.  What's the best weed killer to use for weeds that are growing in your grass and won't kill the grass itself?  I think some weed killers also kill grass, too, right?  

Thanks,

Tachikara

[Ingar_HD_ATL]

Hey tachikara.

I would need to know a couple things in order to give you the best answer.

Where do you live? 

What kind of sod did you put down?

How long has the sod been down?

One thing is universally for sure however. Weed killers do not work when temperatures are below 50 to 55 degrees and It is advisable to put down a pre-emergent weed preventer in late winter, before putting down a weed killer, to prevent most of your weeds that tend to crop up in the spring.

Here in Georgia, we put down our pre-emergent on February 1st because once it warms up then it starts to be too late, as the weeds will immediately start coming up. People living up north will wait a little longer to put down their pre-emergent.

If you are unsure as to what type sod you have, I can narrow it down with a picture or just by knowing where you live.

Hit me back here and I can tell you what to do and when to do it to your lawn.

[tachikara]

Hi, Green Giant,

I live in northern California.  I'm not sure what type of sod was put down.

The sod has been down for ~ 5-6 months now.

I had no idea that weed killers don't work in temps below 50-55 degrees.  Are these day time temperatures or night time temperatures or does not it not matter?  Where I live, these days the day-time high is ~ 60 degrees, but at night it can drop to mid-30's or the 40's.

Thanks for your help.

[Ingar_HD_ATL]

Hey tachikara. 

If you live in coastal Northern California then I would suspect that you have either Centipede grass, Bermuda grass or St. Augustine grass. Each of these grasses look different and each must be treated differently, therefore I need you to send me some pictures of your lawn. An up close shot and a further back shot. 

Just save some pictures to your computer and then as you are replying back to me, you will see the tool bar above with all the icons. Click on the icon of the tree to post pictures. 

Is your lawn brown (dormant) right now? 

Does your grass have thin or thick blades?

I would recommend putting down a pre-emergent weed preventer down on February 1st to prevent any more weeds from coming up and then we can kill the weeds in April, once it warms up and the grass greens up.

It does not matter what the day temperatures are. When the cold nights roll in, it will bring growth to a screeching stop. When weeds are not growing then they wont absorb anything, including weed killer.