Fall Nitrogen Blitz
Fall is approaching. The temps start to cool down from the summer heat. Storms are in the forecast. It is time to start the Fall Nitrogen Blitz. This is just one approach (of many) that I have successfully used and so have others.
If you could only do one thing to your lawn for the entire year, fall nitrogen is it. The second one being spring PreM (pre-emergent). Why fall nitrogen? As air temperatures start to cool down (60-75F), they approach the prime temperature for growth of cool season lawns.. The soil temps are also good (unlike in spring) to promote root growth. Part of the fall nitrogen blitz approach is to provide nitrogen so the roots could recover from the summer damage and store the nitrate as carbohydrates during the winter. This extra build up helps the lawn be more robust during the winter and faster green up in the spring.
Notes
- First, I live in the Indianapolis area. The dates I use are for my area. If you live far north (Canada) then go a month earlier. If you live south of Indy, then delay 2-3 weeks. If you live in Slovenia, try to find a USA state that has similar weather. Check the forum for what other experienced members are doing around your area.
- Transition zone cool season grass can start being fertilized in early September, with the late fall application probably in early December. Top growth might not stop for your zone, but I think it is a good idea to not continue applying nitrogen during the winter. This subject was discussed in the post by @j4c11 Fall Nitrogen in the Transition Zone
- Lastly, this is not intended for a recently (3-4 weeks ago) seeded lawn since the grass is too young to be forced to grow with nitrogen. Let it grow a winter before doing this. During an overseed/reno use a spoon feeding approach.
- Your local university might publish/blog local recommendations based on local research. Find a close one and read their advise.
- Each state might have local restrictions on herbicides and fertilizers. Please research your state and follow the applicable laws.
More importantly, it is best to recognize the signs and not to follow a precise calendar. This post is just a guideline, feel free to experiment. Follow the "What did you do with your lawn today?" post to see what members from your region are doing and ask them for advice.
Fertilizers
The main source of fertilizer should be the fast acting ones. This prevents delayed feeding response from the nitrogen breaking down. I refer to urea (46-0-0) during this article, but it does not mean you have to only use urea. Urea tends to be the cheapest with easy application math (~50% of the weight is nitrogen).
You will find urea at feed stores (~$20 for 50 lb) and it is unlikely you will find Urea at typical home improvement stores (e.g. Home Depot, Lowes, Tractor Supply) so don't bother. It is best for urea to be watered in shortly after application for two reasons: (1) urea pellets resting directly on blades of grass can cause localized "burn" of the blades, particularly if dampened lightly, but not watered in, such as by dew which wets the grass blades and the urea pellets, but isn't sufficient to dissolve the urea pellets into the soil, and (2) urea does start to lose some nitrogen to volatilization to the air, but this effect is not as extreme as sometimes reported. The amount of volatilization per day is highly dependent upon a variety of factors, such as moisture (more moisture is worse), soil pH, and temperature. Therefore it is best for the urea to be watered in with 0.25-0.5 inches of gentle rain or irrigation within 1-2 days of application.
As temperature drops or depending on your soil pH, Ammonium Sulfate (21-0-0) is another great fast acting nitrogen source. I prefer it over Urea.
Also, be careful with overlaps since overlapping will concentrate the nitrogen and could kill your grass. If you want to be safer, you could split the quantity of monthly Urea in half and apply every two weeks (this is what I actually do). For monthly, apply urea at 2 lb/ksqft to provide about 1 lb/ksqft of nitrogen. For biweekly, apply at 1 lb/ksqft to provide 0.5 lb/ksqft of nitrogen.
ALL references are to granular soil nitrogen. If you want to spray (it is a lot of extra work), you need to water in immediately for the rates discussed in this article.
The shed
Depending on the summer (wet vs. dry) but around August the lawn will start growing faster again. It will also look like it is shedding dead stuff. This is the time to starting dropping the height of cut (HOC) from the summer HOC. This also helps the lawn get rid of the dead stuff and prepares the lawn for the fall. The HOC is a very personal choice, but most will be happy with a 2.5 inch height of cut (HOC).
Fall PreM (if not overseeding)
Early August (when soil temps drop) is also the time to apply a PreM barrier, especially if there was a wet or cool summer. The PreM applied in spring has broken down by now or was washed away by the rains. Poa annua germinates once the summer temps drop (Poa A is a cool season grass too), therefore a PreM now prevents it from establishing during the fall. You won't notice now, but next spring you will. I recommend prodiamine at 0.65 lbs ai/acre (0.24 fl oz/ksqft)rate.
Nitrogen
Around mid August (again for Indy), it is time to start dropping nitrogen. You need to apply 1 lb of nitrogen per 1000 sq ft (1 lb/k) per rolling month. What nitrogen? At the beginning(August) it could be any, synthetic or organic (milorganite, corn, alfalfa) or a mix; but consider your cost (since organics tend to be more expensive). The organics will take more time to break down and could lead to a delayed feeding. Early September, switch to a fast acting nitrogen source. See the Fertilizer section above for more details.
So, you will be mowing. Around twice a week, if not more to avoid breaking the 1/3 guideline. Water the lawn as needed (but might not be needed).
The slow down
or the lull, the interlude, the hiatus, the rest, etc
I continue applying nitrogen monthly until around 25 Oct (remember to adjust to your area). This allows grass to slow down from all the nitrogen you applied without forcing more top growth. Since there is less daylight and temperatures are cooler, your grass will start to slow down. This is the natural response as it prepares for winter. What is your job? Just keep mowing. Yep, that's it.
The end of the season (aka winterizing)
You will continue to mow for around a month after the last fertilizer application, until one day you will notice no clippings from your mower. The grass stopped top grow and the roots continue to develop. It is a bittersweet day. You will need to prepare your mower for storage (clean it, dry it and wax it) and get the snow blower out.
Withdrawal syndrome
After all the mowing and fertilizing, now is the withdrawal period. You might notice some folks living in your house. They seem nice and friendly to you and call you Dad (or Mom). Apparently there are a few shows to binge watch on Netflix too.
So, all there is to do now is go to TLF and see pictures from the warm season side or the Australians. Maybe they are scalping or playing with sand. Maybe it is time to learn about Bermuda. You might also get to learn from the Australian members or start planning for next year.
PS
So if you read all of this, there is one thing I left out to not focus on it. There is a more intense form of nitrogen blitz. Instead of 1 lb/k of N per month, you apply 0.5 lb/k of fast acting N per week. Yes, that yields 2 lb of N/k a month and yes, you will be mowing. It is like the grass grows behind you as you mow. The main benefit I see to it is if you need KBG to fill large voids. In my opinion, an established mature and dense lawn doesn't need it and it is a lot of work. It's really necessary to use a fast acting nitrogen (urea/AS) and it needs to be watered. I've done it the year after a renovation and it spreads the KBG.
PS2
I move this traditional last task as an option. For those of us old school in Fall Nitrogen, it might be weird why the change. New research has found that this last step shows very few benefits and it is not environmentally friendly. @osuturfman discussed a new model in ATY that uses 50% slow release, but what I describe is a hybrid using fast release. UNL actually changed their fall recommendations in 2014 to avoid the late fall nitrogen. Therefore last year, I decided to skip it in a portion of my lawn as a trial. The results were that I could not tell the areas apart during the winter and spring. I tested it at 1.5 HOC and 3in HOC too. This year I'm just going to skip it. The very late fall nitrogen application is one of the hardest things to time properly. I know habits are hard to change, so I challenge you to give it a try in a portion of the backyard and share your observations next year.
Here are the steps if you choose to do this:
Once growth stopped, you have a period of 3 weeks (or before the ground gets frozen) to apply 1 lb/k of nitrogen from a fast release source. This means urea or ammonium sulfate (not organics and not coated big box stuff called winterizer). Yes, you will be applying fertilizer to grass after the blades have stopped growing, but the roots are still active and will save some of that nitrogen through winter and spring.
Remember the comment above that Urea needs watering? Yes, this is the most challenging aspect. In ground irrigation won't help since it is likely blown and winterized. So, you need to watch the weather and do a rain dance to hope for rain within the 3 weeks since growth stopped. If no rains shows up, then you will need to drag a hose and sprinkler out and water the lawn before the ground freezes. So far, I have never needed to do this and I don't know how i would be able to explain it to the wife.
Collaborators
Virginagal, K&N, LIgrass
Sources:
Turfgrass Fertilization: A Basic Guide for Professional Turfgrass Managers
Dollar for dollar, fertilization does more to improve poor-quality turfgrass or to maintain good-quality turfgrass than any other management practice.
plantscience.psu.edu
Benefits of Late Fall Fertilization
The Benefits of Late Fall Fertilization A. J. Koski and John R. Street Late fall nitrogen fertilization Late season nitrogen fertilization has been practiced by professionals for some time, but the wisdom of this technique continually needs to be reviewed and this fall (2010) more than ever due...
turfdisease.osu.edu
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