I recently used my local extension service to do a soil test. I did this before I fertilized for the spring so I got a post-winter reading on the soil. They said my lawn was very low in Phosphorous, Potassium, Calcium, and Magnesium:

  • Phosphorous: 1.8ppm, optimum range is 4-14ppm
  • Potassium: 25ppm, optimum range is 100-160ppm
  • Calcium: 244ppm, optimum range is 1000-1500ppm
  • Magnesium: 31ppm, optimum range is 50-120ppm

In their recommendations they said to add dolomitic limestone due to low magnesium. They also said to apply varying amounts of N-P-K to amend the other nutrients that were low. They recommended 2-4lb N per 1000sqtft, 2lb P per 1000sqtft, and 4lb K per 1000sqtft. I'm struggling with finding a great fertilizer that can add all of those nutrients in the right ratios (other than N, that's an easy one). Are there other ways to get more Phosphorous, Potassium and Calcium in my soil? Would the dolomitic limestone help any of those in addition to helping the low magnesium?

Images of the test results are below: results recos

  • Do you know how to figure how much to use? How to translate their recommendations in pounds of Nitrogen to your bag of fertilizer? A 50# bag of fertilizer with 19% Nitrogen would have 9.5 pounds of NITROGEN which means @2# per 1000 this bag would fertilize 9500 sq. ft. At 4# per 1000 sq. ft. this bag would fertilize 4750 sq. ft. How big is your lawn? At 7% Potassium = 3.5# K in your 50# bag. The potassium in this bag isn't even going to be sufficient even for 1000 sq. ft. And certainly no Phosphorous. If your lawn is 5000sq. ft, you've done enough with nitrogen. You will need 10# P...
    – stormy
    May 5, 2017 at 18:26
  • Arghhh, check my math please...10#P and 20#K. So I'd get a 50# bag of 0 - 10 - 20....this bag will fertilize 5000 sq. ft. of lawn with 5# Phosphorous and 10# Potassium. We have to deduct for the 3.5# you've already added of Potassium. 20# less 3.5# = 16.5# You should see or you already see that getting the perfect formulation ain't happening. Getting close works fine, but never overdo. In fact HALF of what they recommend would work better. That poundage should be split into thirds, as their recommendation deals with the entire season.
    – stormy
    May 5, 2017 at 18:37
  • 1
    Here is an article on lime that you can cogitate upon, grins. braenstone.com/2014/12/agricultural-lime-vs-dolomite-lime What was the soil test for Nitrogen? Could you take a picture of your soil test and add it to your question? This is pretty cool. Tell us how much you paid for it and who prepared this test? That would be helpful. Did you have any choices of different tests or additions such as...organic matter, soil composition? Soil tests put YOU in the driver's seat. Makes a basis for all your decisions! We rarely discuss how to interpret and how to use these tests!
    – stormy
    May 5, 2017 at 18:49
  • Sorry for the late response. Soil test was done by UMass extension for $15. I did not do any add-ons like the organic analysis, etc. I am adding a screenshot of the test results right now... May 11, 2017 at 23:31
  • Excellent J. dillinger!! Do you see how they talk about 'splitting' the applications into 3 or 4 to get the soil chemistry up to snuff? Every application helps. Just keep track of exactly what you've spread, how much, the formulation and any micronutrients, when you applied and gee towards the end of this season, I would get a second test to see how your materials and amounts have changed your soil. I'll definitely look at these references they've sent. So might I ask kind of a pop quiz, grins, what do you think your next step should be? Everything is low except Cu, Zn, Fe, Al and Pb
    – stormy
    May 11, 2017 at 23:52

3 Answers 3


I would be careful about buying pre-mixed fertilizers without researching them (and how the chemicals interact with each other). Sometimes, they add two ingredients wherein one makes the other less useful. Studying up on chemical salts and how they respond to each other can help you to make a better decision if you're going to get pre-mixed fertilizers. I also recommend learning which chemical salts kill beneficial microbes (e.g. potassium chloride and calcium nitrate) and soil flora.

I don't see any mention of nitrogen levels on the test (just recommendations of how much to add). That would seem kind of unusual, I suppose, but as you're dealing with grass, and you're adding both calcium and potassium, then adding a reasonable portion of nitrogen probably isn't going to hurt, even if you don't need it per se (unless it's very high).

Wood ash contains a fair amount of potassium and calcium. I'm not sure how grass responds to it, but tomatoes sure seem to enjoy some. Wood ash will raise your soil pH.

Greensand is often thought to be high in potassium, and although it does add some, it doesn't add very much; it's probably more helpful for adding silica and changing soil structure.

Bone meal is a natural source of calcium (and other minerals) and phosphorus. I think it may be slow-release. However, if you're getting it to be natural, realize that the stuff they fed the cows whose bones are being used may or may not meet your approval.

Compost can be a good natural source of nitrogen, nutrients and beneficial microbes. Again, if you're composting stuff that isn't organic (e.g. treated with pesticides etc.), some of that may still be in your compost.

I might recommend adding some monoammonium phosphate (you can get granular as well as water soluble). That should add a little nitrogen and a lot of phosphorus. It's not approved for organic gardening, but it seems to be one of the better and safer forms of phosphorus, as far as I've found.

Monopotassium phosphate is great for adding both phosphorus and potassium. It's also not approved for organic gardening and is also one of the better and safer forms of phosphorus, as far as I've found.

Potassium sulfate is good for just potassium. There are forms available that are supposed to be suitable for organic gardening, and there are forms that are not.

I've ordered monoammonium phosphate (both the granular and water soluble forms) and monopotassium phosphate before from Greenway Biotech's website (fast and free shipping; their products seem quite pure and effective). I've ordered AlphaChemicals brand potassium sulfate from Amazon and eBay (mine was purer on Amazon than eBay). I've had good results with all four of these for garden plants (much better than results I've had with pre-mixed fertilizers). I haven't tried these things on lawns, but I thought you might appreciate the information anyway.

I've tried ammonium sulfate and urea from Greenway Biotech's site, too, for nitrogen; the ammonium sulfate has faster and stronger results, in my experience (and is advertized as being good for lawns), but both work better used together on all the plants I've used them both ways with. You might be tempted to use nitrate fertilizers, but be aware there are a lot of issues you might like to know about with those (like toxicity, killing beneficial microbes, stimulating weed germination, and interacting with other fertilizers). However calcium nitrate would add both calcium and nitrogen, and there are likely lots of fertilizer components that interact with others.

AlphaChemicals seems to claim their potassium sulfate is certified for organic gardening (although I haven't been able to verify this). That's the only reason I'd buy their potassium sulfate over Greenway Biotech's, but Greenway Biotech is my favorite place to get fertilizer components and plant nutrients. They have a lot of stuff.

What I've tried from Greenway Biotech all seemed very pure and good (buying directly from their website, rather than Amazon, is nice because they give free two-day shipping by default, and you know for sure it's really the company it claims to be; Amazon's great, and I shop there a lot, but sometimes you have to be careful of companies that seem to be the real company, but actually aren't).

Speaking of purity, you might want to study how various fertilizers or fertilizer components are made (some may be contaminated with such as fluoride or heavy metals due to the process). I researched that sort of thing for a good while before I decided on monopotassium phosphate and monoammonium phosphate for my go-to phosphorus fertilizers.

If you're worried about phosphate fertilizers leaching into the water table, then get the granular kind, which isn't meant to dissolve in water, per se. You may want to get more of it, though (in my experience, it's easier to use up the granular kind faster). If you have a clay-type soil, I imagine phosphorus leaching to the water table might not be as big of an issue as with a soil that drains super fast. I imagine clay filters more phosphorus out, but I could be wrong.

Rock phosphate is another non-water-soluble source of phosphorus. Plants seem to like it, but you'd get a lot more phosphorus from one of the phosphate fertilizers I mentioned above (and there are probably fewer heavy metals in them, too). It's slow-release.

Worm castings can add microbes to help bring out the natural phosphorus in your soil.

Dolomite lime should add both calcium and magnesium as another answerer said. It will raise your pH (and that's usually what people use lime for).

Epsom salt is magnesium sulfate, which also might interest you for magnesium. I'm not sure it's an ideal form, though (at least in our soil), but lots of people tout it for plants as being awesome.

Basalt rockdust has plenty of calcium (and other minerals, especially silica), although I'm not sure how grass likes it offhand. The kind with humic acid added is probably going to have better results to start with (although I haven't tried it), but I have tried the microfine kind, which is pretty cool, and the regular kind (the latter two at least, will raise your pH, however).

I haven't studied the fertilization and nutrient needs of grass much, but this should help you know some alternative sources for fertilizer components and minerals. I definitely recommend reading more about it, as there's assuredly much more to learn (especially as lawns are so common that there is probably a wealth of ideas and information available).


The dolomitic limestone is limestone and thus has calcium. It's just that the "dolomitic" tag means it also has magnesium, so it should cover both of those needs, and that's likely factored into any suggested application rate they might have provided.

Don't stress too much about finding a fertilizer with the precise (given you have ranges, not so precise) ratio - you can use more than one to get what you need. So some 1-1-1, 5-5-5 or 10-10-10 up to the level of phosphorus you need and then either use 0-0-x and x-0-0 (or y-0-y) to fill in the N&K, unless you happen upon some 2-1-2, 1-1-2, 4-4-8, or 10-5-10 in your hunting.

How you get there is up to you - I'd reach for wood ash, granite dust or greensand for potassium (aka potash) and a little phosphorus. More phosphorous from steamed bonemeal, N, as you say, is easy.

If you'll be buying whatever, you might get Alfalfa Pellets (3-1-2) as less likely to interest dogs than bonemeal and not too far off the mark for what you need. Spread some greensand or granite dust to tweak it.

However, most recommendations are to spread the fertilizers at one point in time (such as spring) and the limestone at another (such as fall) rather than all at once.

  • Thanks, this is good to know. So after I took the soil samples I thought the soil test would take weeks so I went ahead and did fertilization before the crabgrass germinated. I applied late April with LESCO slow release pre-emergent 19-0-7 @ 50lbs but I didn't use all of it because 50lb was more than needed for my lawn size. I imagine I should calculate what I was missing for the P and K and just amend with the things you mentioned? But wait till fall maybe? Also, I will look into Alfalfa Pellets because I have a dog. May 5, 2017 at 15:52
  • Fertilizer won't affect your dog unless he is a voracious lawn licker. Was there a cautionary statement for pets because of the preemergence? Fertilizer and preemergence chemicals once watered into the lawn should cause no problems, unless that label says differently. DOGS. I've got these 2 male puppies; I swear, they will find and get into or ruin the ONE thing you hope they don't find. A sixth sense?
    – stormy
    May 5, 2017 at 18:03

Great job getting a soil test. What plants are you wanting to plant? Did that soil test give you your pH? Limestone will only raise the pH making other chemicals available to certain plants. This is just showing that you need to add chemicals to your soil for MOST plants. What you want to grow (blueberries? tomatoes? potatoes? need a more acid soil to be able to uptake the chemicals), and what the soil tilth is makes a huge difference in your choice of fertilizer. If you want to grow acid loving plants, this lime is not recommended.

Since this is for your lawn, you need to know the pH. Slightly alkaline (over 6.5) is necessary. Lime definitely is good for lawns IF your soil is below 7. Aeration is critical. I found that this ORGANIC lawn fertilizer (the one I used was Dr. Earth) was as different as night and day compared to fast release 'Scotts' or 'Ortho'. Worth every penny and lasts far longer than the synthetic stuff.

If this is your lawn, go find those la la organic fertilizers like Dr. Earth's Lawn Fertilizer. Doesn't matter the brand but look at the chemistry. I was blown away and I am a lawn 'expert' so to speak. And I am not so swayed by la la organic anything. Blown away!! Keep your grass mowed on HIGH no shorter than 3" if you have cool season grasses! I am not kidding!

What was the pH? They should have had that in the test.

  • Forgot to mention that the pH is 5.4. Also, I fertilized in late April (after I took the soil samples) with LESCO slow release pre-emergent, 19-0-7 @ 50lbs (didn't use the whole bag because it was more than my lawn size) May 5, 2017 at 15:49
  • WHOA...that is way too low, too acid. You definitely need to lime. Your fertilizer had no phosphorous included and your soil test showed huge deficiency in Phosphorous. Honest injun, J! The next fertilization go get Dr. Earth's Lawn Fertilizer. I don't get 'blown away' often and with caring for thousands of lawns, this fertilizer blew me away. Gotta just try it and tell us what you think. Take a picture before and then after. Takes longer to see results but you will. What do you mean LESCO slow release PRE EMERGENT?
    – stormy
    May 5, 2017 at 17:45
  • I've got to reread before I comment, sorry again. Crabgrass grows 2 ways; one by roots and the other by seed. If you keep that grass mowed on high high high, those seeds will not germinate. If you allow the soil to dry out inbetween watering those seeds will not germinate or at least they will wither with shallow roots while the healthy grass digs deeper for the water. Water dries in the soil from the top down. How long does this preemergent last? You won't be able to reseed until that stuff is gone, no big deal. We want to lower your energy input for this lawn, right?
    – stormy
    May 5, 2017 at 17:56
  • Shoot, the crabgrass roots that are already there will not be affected by this preemergence. Just saying.
    – stormy
    May 5, 2017 at 17:57

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.