It's too late to do anything about the weeds now. They will die off soon with the lower temps, and any weed killers you use now will negatively affect the seeds you just put down. Most weeds are annuals which die off in the fall after they have dropped their seeds. The seeds germinate when conditions are right next year. Next spring, use a preemergent like halts or dimension, and again in early summer. This will greatly reduce your weeds in the summer. Any weeds that are left in your lawn next summer you can hand pull or kill with a product like weed-b-gone, which is very effective at killing weeds and not your grass as long as you read the label and follow the instructions. It's a good rule of thumb to always follow instructions with any lawn product, the last thing you want to do is kill the grass you worked so hard to grow. Personally I would stay away from fertilizer with weed killer. Stick with separate products. If you just overseeded then why do you want to overseed again? The latest I would put down seed in NJ would be probably the middle of this month. Also why did you use weed killer in the fall?

i must have mistyped, i did not use fertilizer with weedkiller. i only did that in the spring. i was hoping to overseed twice in the fall to thicken the grass. thanks for the advice, i will wok=rk harder in the spring on the weeds!

When is your average first frost? You should usually try to seed no later than 6 weeks before the average first frost. If you've missed that, you can also dormant seed. To do that, wait until the soil has cooled off enough that the seeds won't germinate and spread the seeds (some people like to do it just before the first snow storm). The freeze/thaw cycles and the snow melt will help bring the seeds into contact with the soil. In the spring, when the soil warms enough, the seeds will germinate with the natural moisture from snow melt and spring rains. This approach gives a bit of a head start when compared with a typical spring seeding because the seeds are already there when the conditions are right.

But I wonder if there is more going on there. It's a little unusual to need to overseed a second time in the fall. Did you get poor germination? Did you seed too thinly?

If you seeded at the correct rate and got good germination, it might be a mistake to seed again. The reason is that if you get too much grass growing in too small an area, there will be too much competition for the resources and the grass will suffer and some will die out.

If you seeded with Kentucky bluegrass you should not need more seed. If you seeded with fescue into a fescue lawn, then you are on the "Seed Every Fall for the Rest of Your Life Plan." Fescue is a 'bunch grass' and does not spread to fill in thin areas. KBG is a sod-forming grass and spreads to fill. My preference is for sod-forming grasses.

i used a mixed seed, northeastern mix by penningtons. i just overseeded, so im not sure how successful it was yet. i think i will try to dormant seed with kgb. thank you!!

If you just seeded and don't know how successful it was, I would hold off any any further overseeding. The northeastern mix almost surely has some KBG in it, so it will take time to come in. It will also fill in bare spots as it gets established.

If you dormant seed on top of that, you could end up with too much new grass. That may seem like a good thing, but it isn't. People who do that end up with grass that struggles and often dies.