proportions of variious chemicals you recommended for my lawn

Asked April 7, 2020, 3:18 PM EDT

I did a soil sample test and have the results but dopnt know exactly what amounts I put in my brodcast spreaded. Please help.

Ramsey County Minnesota

8 Responses

Your soil test results should indicate the fertilizer analysis recommended based on your test results for P (phosphate) and K (potash). N (nitrogen) is always recommended because it is a mobile nutrient and moves through soil, making replenishing necessary. MN soils are typically high in P and it's likely your middle number (P) is 0.

You'll want to purchase a fertilizer that matches or comes close to the recommended NPK on your test results. Because N is mobile, it takes priority of the P and K, and you'll want to buy a fertilizer that matches your recommended N as closely as possible. For example, if the test results indicate you need 20-0-8 (20% N, 0% P and 8% K) and your local store has a choice of 10-0-8 or 15-0-10, it would be better to buy the 15-0-10 because it more closely matches the recommend 20-0-8.

If you go to the Soil Test Lab website, you'll find a good explanation:

Here are a couple resources including how to calibrate your spreader.
Calibrating your fertilizer spreader from U of New Hampshire

Fertilizing Lawns

Some more lawn care resources:
Essential tips to a healthy lawn Part 1
Essential tips to a healthy lawn Part II

If you have follow up questions, you are welcome to reply to this response.

Results were as follows: Phosphorus = 6, Potassium= 99, Ph= 7.8, Organic matter=5.4. I have purchased a 12 lb. bag of Scott's 21-22-4, a 12lb bag of Scotts 32-0-4 and a 4lb bag of Muriate of Potash 0-0-60. I believe this should cover all my needs. I'm covering about 5,000 sq/ft. Id like to make a single pass in my broadcast spreader with all three ingrediencies in the hopper. If I use say, a 12 oz measuring cup, to add the ingrediences. what proportions should I use to make my batch?
Thank you!

What was the recommended fertilizer analysis from the soil test lab?

Lime -0, Nitrogen- 2 lbs per 1,000 sq/ft, Phos - 1 LBS/1000 sq/ft, Potash 2Lbs/1000 sq/ft, and proportions of the nutrients 20-10-20

I am surprised you need any P - most MN soils are naturally high in P.

If you are using a Scott's spreader, the bag should give you guidelines on the correct settings for your equipment.

Of the 3 products you purchased, the Scott's 21-22-4 is the best match to the recommended NPK analysis of 20-10-20. Of your 12 lb bag of 21-22-4, you'll need 10 lbs to cover 5000 sq ft (2 lbs N / 1000 sq ft = 10 lbs N / 5000 sq ft). As I mentioned before, you want to get as close to the recommendations for N first as it is a mobile nutrient and thus needs to be replenished.

You'll need to supplement with some of the muriate of potash as your Scott's product is only 4% potash and the recommendation is 20%. You'll want to add about 1 lb of your 4 lb bag to the 10 lbs of 21-22-4. This will bring you up to 20% potash (4lbs / 60 % = 1.07 lbs / 16; 16% is the remaining amount needed to bring your potash up to the recommended 20%)

As for the other Scott's product, I would see if you could exchange it for more of the 21-22-4. With each application, use 10 lbs of the 21-22-4 + 1 lb of the potash. Your potash will last the season, but you'll need more of the 21-22-4.

Thank you for your help.
I do need to make a correction though. The Scotts bag weighs 21 lbs. I made a mistake in my typing. Will this effect my ratios.
Bag states—- 21 lbs will cover 5000 square feet . Sorry for the mistake

No problem.

Based on the soil test recommendations though, I believe 10 lbs would be sufficient to cover 5000 sq ft at 2 lbs N / 1000 sq ft. Without looking at the bag, I'm not sure. You could mix batches of 10 lbs of 21-22-04 + the 1 lb of K, set your calibration on your spreader and apply. You can always add another batch and apply (you likely will have to anyway due to how much your spreader holds).

Thanks again!