New Lawn - Weeds During Germination
Hello Experts, I have started growing a new lawn in Southern Maryland. 7 days after germination and 13 days after putting the seed down, I have started to see the attached weed throughout my lawn. They seem to be more prevalent in areas of lower germination. Do you have any advice on what to do about weeds at this stage of planting a new lawn? Thanks!! Here is a link to my lawn journal if it helps:
St. Mary's County Maryland
These are chickweed seedlings. Chickweed is an annual--what's known as a "winter annual", i.e. it germinates in the fall, keeps a low profile during the winter, which puts it in a good position to explode with growth in the spring. It is in the Weed Gallery on our website: https://extension.umd.edu/hgic/topics/common-chickweed
You cannot apply an herbicide now. Concentrate on making your new lawn as thick and vigorous as possible. If some chickweed is competing with your lawn in the spring, you can address it then. It is short-lived and mowing and a thick lawn usually is all that a lawn needs to control it.
If you have not done a soil test, do so now: https://extension.umd.edu/hgic/topics/soil-testing Your lawn may need extra fertilizer or lime. (If the pH is too low, it can have all the nutrients in the world but not be able to use them.)
Keep in mind that lawns should be fertilized every fall, or they will thin out.
Here's a good page on successful lawn management: https://extension.umd.edu/hgic/topics/lawn-renovation-and-overseeding
Ok thanks! That makes sense.
I've seen a lot of people online suggesting to use herbicides like Tenacity while starting a new lawn to prevent weeds from growing. Do you not recommend this?
Tenacity is primarily a post-emergent (affects already-germinated weeds), though it does have some pre-emergent (affects only germinating weeds) ability as well. Its main advantage is that is allows for relatively easy over-seeding of turf, whereas many pre-emergent herbicides will kill turf seed as well as weed seed.
At this point, the turf seedlings should first reach mowing height and then be mown three times prior to any application of herbicide, so they are more mature and tolerant of the chemical exposure. (Therefore, they need to wait about three weeks if growing at the rate of needing mowing once a week.) You do still have time this season to do this if you wish. Check to make sure Chickweed is a species on the herbicide label that it works to control. You can follow-up in spring with a post-emergent for the Chickweed again, but it's not likely it will be needed as a vigorous, dense turf should out-compete them, and mowing will reduce the Chickweed's ability to flower and set seed as well.
See the final paragraph and images on this page about potential temporary discoloration to turfgrass from Tenacity: https://extension.umd.edu/hgic/topics/chemical-injury-lawns
And just to check my understanding, I was told that if the pH of my soil is too low, that the grass cannot access the nutrients (NPK). Is this true for weeds as well? Or do different plants (grass and weeds) uptake nutrients better at different pH levels, with weeds doing better in more acidic soil?
I'm a little confused about how some weeds can grow so well but my grass seems to struggle. I had a soil test and my soil is fairly acidic.
pH does influence how nutrients are able to be absorbed by plant roots, yes, and it is true that different plant species can have different abilities to absorb nutrients at different pH values. Your pH is a bit low for ideal turf conditions, so applying lime would help to raise it to a more lawn-appropriate level. Labs should provide liming recommendations, but if not, the bag of lime itself usually gives guidelines on pounds needed per thousand square feet to raise the pH from a known starting point to a given end point. (There's often a chart to follow.) Here is more liming info: