I’m a big fan of organic liquid fertilizer.
But there’s also an important use for organic dry fertilizer.
I use liquid fertilizers mainly to provide small amounts of 80+ nutrients directly as a plant fertilizer, and also as a soil fertilizer.
Doing this plays a big part in helping me grow nutrient-dense food.
And yet some nutrients we need in the soil more than others, the big three in the organic world being calcium (Ca), phosphorus (P) and potassium (K).
We need to have enough of them in the soil, but not too much.
(I know that npk fertilizer is stressed in the conventional world, and yes, nitrogen fertilizer is sometimes useful too, but it’s really not all that hard to get enough nitrogen – calcium is much more important to get right, so that’s my focus today).
The benefits we get when we move those three minerals in our soil towards the ideal amounts are many: healthier plants, fewer pests and weeds, better soil structure, etc.
That’s where dry fertilizer comes in…
Homemade Dry Fertilizer?
Today I was hoping to continue that journey with the big three nutrients listed up above.
A difficulty, though, is that we need a lot of them, not just a little.
So while spraying some ocean water or liquified seaweed can get us a lot of the micronutrients we need, it’s harder when we need several pounds of the above three minerals per 1000 square feet.
That’s why when I need to really boost one of these minerals in the soil, I’ve always gravitated to specific dry fertilizers like lime. They’re inexpensive and easy to use.
But I wanted to see if there’s a way to do this at home, so here we go…
The vast majority of soils are deficient in calcium.
Usually the best way to get it back in there is a dry fertilizer like calcium carbonate (aka calcitic lime or high-calcium lime).
And fortunately we have plenty of lime deposits all around the world, so it’s a fairly sustainable resource.
In fact, this is the only mineral I recommend almost everyone should add, even if they don’t have a soil testing showing they need it.
I would rather you get a soil test so you know for sure, but I know most people don’t do that.
And I don’t want you to add a lot – just 10 pounds per 1000 square feet of calcium carbonate, as we don’t want to overdo it. Only a soil test will tell you if you need more than that.
But those 10 pounds will be beneficial for over 90% of soils, and will rarely cause any issues.
There already tends to be enough soil calcium in much of Colorado, Montana, northern Iowa/southern Minnesota, and parts of Texas, but most soils need more.
Ten pounds of calcium carbonate is going to supply about 4 pounds of calcium.
By the way, it’s also a very important grass fertilizer, because lawns really need calcium for many reasons, but especially to combat compaction.
Is there a way to get calcium without buying lime?
Well, maybe. Let’s start with eggshells. Many people have them, so that’s a good beginning. They’re mostly calcium carbonate, which is perfect.
The only problem is that they’re rather small. There’s about 0.8 grams of calcium in an egg shell, so to get that 4 pounds of calcium, you would need about 2300 egg shells.
If you’re gardening only 100 square feet, then you’d only need 230 egg shells, which is perhaps… well, still a lot.
So yes, I sometimes use egg shells in my gardening, but mostly for houseplants or a handful of prized garden plants.
It’s the same kind of math with other food products. There are 1.2 grams of calcium in a quart of milk, so you would need about 1500 quarts of milk to get that 4 pounds of calcium.
That’s a lot of mooing.
I do have a solution that’s much more plausible, if you have access to it, and that is wood ashes from a fire.
Ash often contains 10-20% calcium, a decent amount – along with many trace minerals.
The main issue is that it also contains perhaps 4-8% potassium. Now, potassium isn’t a bad thing unless we have too much of it, but most of us already have enough, so we usually don’t want to be adding more.
While it’s probably okay to add 10 pounds of wood ash to your soil per 1000 square feet, which will give you 1-2 pounds of calcium, I wouldn’t go adding much more than that unless you have a soil test telling you that you need both calcium and potassium.
And be sure to add it in the dormant season, because it’s hard on biology if applied while microbes and plants are working away.
Think of it kind of like a chemical fertilizer in that regard – it’s much better if it has time to mellow out in the soil for at least couple of months before planting. Ideally, you’d save your ash from the winter until the next fall and apply it then, to give it the winter to acclimate.
Potassium is a quick one because most of us already have enough of it.
If you’re using even a small amount of compost or manure, you probably have all the potassium you need.
Those materials have less than 2% potassium, but that’s all we need.
We need about 15 times as much calcium as both potassium and phosphorus, so calcium is the big one.
Gardeners who use a lot of compost/manure often end up with too much potassium, which leads to all kinds of issues, especially calcium deficiency and soil compaction.
But if you have a soil test showing that you do need potassium, compost is a great source.
Banana peels contain about 8%, so they’re a good source if you happen to be blessed with an abundance of banana peels.
Wood ash, as we’ve seen above, is a good source if you also need the calcium.
The 2 main potassium dry fertilizers I like are K Mag and Greensand. K Mag is a high quality fertilizer if you need potassium, magnesium and sulfur, since it contains all three. Greensand is better if you just need potassium.
Phosphorus is probably the second most important mineral in the soil after calcium.
We need the same amount of phosphorus as potassium, but it’s far more common for our soil to be deficient in phosphorus.
Compost contains about 1% phosphate, but since it contains on average about 4 times as much potassium, we max out on potassium before we get our phosphorus up where we need it.
Having more potassium than phosphorus in the soil is the cause of a lot of issues.
So we have to look elsewhere.
If you have access to a pile of bones (I won’t ask why), you’re good to go. You just need to find a way to grind them up. Or put them into a hot compost pile and make some phosphorus-rich compost – they’ll disappear fairly quickly.
I forget where I read this, but some fruit trees were once planted in a very old graveyard, perhaps by accident because the existence of the graveyard was no longer apparent, and when they went in and excavated everything many years later, the roots of the trees had grown all along the skeletal systems of the people buried there, assumedly mining the phosphorus and calcium.
So yes, bones are good fertilizer.
You can also buy bone meal, a dry fertilizer that’s been used by organic gardeners for a long time.
The only issue is that it can carry the prions that cause mad cow disease, as well as relatively high levels of heavy metals. These things may or may not be all that big of a deal, but it’s generally not allowed in the organic standards for that reason, so I’ve tended to stay away from it.
But it is about 12% phosphate. Quite good. And it has a lot of calcium, too, although calcium carbonate is considered a more ‘available’ form of calcium for the soil.
Instead I use soft rock phosphate, a highly available form of phosphorus that also contains calcium and many trace minerals.
It’s labelled as only about 3% phosphate, but that’s just because of the weird way those percentages are calculated. It actually contains a lot more phosphate than that, in line with bone meal.
Dry Fertilizer Summary
But when it comes to correcting specific soil deficiencies, it seems picking up an organic dry fertilizer such as calcium carbonate or rock phosphate is often the way to go.
You can use a dry fertilizer applicator like a spreader, or just your shovel or even your hand (always a good idea to wear gloves).
And I have no problem using a bit of fertilizer if it’s going to help me produce more food with more nutrition.
But I still like to think locally as much as possible, so if you have any ideas for how we can get large amounts of calcium, phosphorus and potassium, let me know below.
Certainly urine has some phosphorus and potassium, but much more nitrogen, so while we should definitely use it, we max out on N before we get to the P and K.
And compost/manure is a decent source of P and K, but if we apply enough to bring up our P, we’re going to have an excess of K.
Any other options?
Feel free to ask questions below or let me know if you have any other ideas…