Overseeding lawn Southern Oregon

Asked May 11, 2015, 5:45 PM EDT

My lawn is full of weeds so my neighbor sprayed weed killer on it. I want to overseed and know I need to mow short , seed and take a bit in also apply compost or topsoil. Should I also apply fertilizer? I just put Scott's weed & feed on last week. I don't want to waste money & time. But neighbor says ok to overseed now. I thought was a fall process. Please help Thank you

Josephine County Oregon lawns and turf horticulture

3 Responses

Hello,

Your question is a bit confusing to interpret because you say your neighbor sprayed your weeds and then you say you also put weed and feed on it. Then you ask whether you should fertilize.

Before I answer your question about seeding, I would like to help you understand the products you are using. First, weed and feed is a combination of a fertilizer and a herbicide. If your neighbor sprayed your lawn to kill the weeds, he also applied a herbicide. If these are the correct facts, you have made two herbicide applications. Making two herbicide applications is not necessarily a bad thing if you apply them correctly with the correct interval between applications. However, I would caution you to be careful with lawn herbicides including weed and feed because they can damage or even kill your lawn if the rate gets too high. Generally, you need to wait at least 2 weeks for a second application. Some labels now require waiting 4 weeks before a second application.

As a side note, weed and feed products have done a poor job of killing weeds in my trials. They usually kill only about 50% of the weeds with one application. A better approach is to hire a licensed pesticide applicator and have them make 2 spray applications 2 to 4 weeks apart. If done correctly, this will kill 99% to 100% of your weeds and you will not have to apply weed and feed every year. If your lawn is mowed regularly, fertilized 2 - 4 times per year (one way to remember when is to think the "Holiday Plan" - Memorial Day, July 4th, Labor Day, and Thanksgiving) and watered in the summer, you will have very few weeds encroach because you will have a dense, healthy lawn with no place for weeds to get started.

Since you have already applied a fertilizer as part of your weed and feed, you likely will not need another fertilizer application for at least another month. If your grass is dense and green, you do not need to apply fertilizer. If you lawn starts losing color or getting thin, then it is time to make another application.

As far as over seeding goes, spring (April 15th - June 15th) is a good time assuming you are going to irrigate your lawn in the summer. Make sure you rake the spots before you over seed to get good soil to seed contact. If the area is too big to rake by hand, you can rent a dethatcher to do the same thing. Dethatching will not hurt your existing lawn as long as you do not over do it. Once you over seed, you need to keep the surface consistently moist for 7 - 10 days. You may have to water for 5 minutes 4 times a day if it is hot. As far as what seed to use, stay away from anything that says "annual ryegrass" or "Italian ryegrass" as this grass will only live for 1 year and then die. I would recommend perennial ryegrass or perennial ryegrass mixed with fine fescue. It's also o.k. if it has some Kentucky bluegrass in the mix. Generally, any named variety will do just fine, except 'Linn' Perennial ryegrass.

After about 8 weeks, you can begin watering every 2 or 3 days, which is the best interval for a healthy lawn in spite what the water purveyors say ("once per week"). If you want to water once per week, that is fine but your lawn will not be as nice.

Do not apply compost, it is a waste of time and money. Compost does have nitrogen in it and will green up your lawn if you apply a thick coating, but you can green up your lawn much easier with fertilizer. Only apply soil if you need to smooth out the low spots.

Good Luck.

Thank you. Yes it was a bit confusing but you answered my question "). One more thing, do I need to 'scalp' the lawn prior to overseeding? I'm sure you would have mentioned it if I do. Meaning now super short. I appreciate your response.

Hello,

You need to mow the lawn short enough so the seed will fall to the soil and not get hung up on the leaves. If you dethatch the lawn first, it should thin the lawn out quite a bit and leave an open canopy for the seed to fall through. Also, if you apply the seed when the grass is dry, you can hand rake the grass after seeding using a big plastic leaf rake and the seed will fall to the soil.

It is a judgement call how low you need to go, but you can tell by looking at the lawn. After dethatching, I would mow it at 2 inches with a bagging mower to remove the debris that was not removed from hand raking. It will do a better job picking up the debris if you mow it twice. Look at it after mowing and see if there are gaps for the seed to fall through. If you don't think it is good enough, you can work the height down from there. Mowing lower will definitely give more gaps, but it will likely not be much additional benefit to go below 3/4". Your mower may not go this low anyway. If you have been mowing infrequently, or really high 3+ to 4", I would error on the side of keeping the mowing height higher - say 1.5" at the lowest before seeding.

If you do dethatch it heavily and mow it down, you should apply twice the normal rate of fertilizer (2 lbs of nitrogen per 1,000 sq. ft.) and water it in so the grass can recover. Otherwise, apply only 1 lb of nitrogen per 1,000 sq. ft. To figure out how much fertilizer to apply to get 2 lbs of nitrogen, divide 2 by the nitrogen percentage on the bag. The nitrogen percentage is the first of 3 numbers on the bag shown as "25-3-15", for example. So, in this example, take 2 and divide by 0.25, which equal 4 lbs of fertilizer per 1,000 sq. ft.to give you 2 lbs of nitrogen per 1,000 sq. ft.

Good luck.