Cyn’s Simple Guide to Fertilizing

The complexity of soil nutrition can bog you down. A super-simple understanding of all things N-P-K helps beginning farmers like me get started.

by Cyn Cady

Cyn's Simple Guide to Fertilizing - Photo by USDA/Flickr ( 

In the dead of winter, when I was busy browsing seed sources and gardening tips online and in catalogs, everything seemed possible. It was then that I made a solemn vow to master the secrets of fertilization by the coming spring.

Spring is springing, and have I done a thing about learning how to dial in fertilization? Nope. Still can’t really remember what “NPK” means, or when to use 5-5-5 instead of 6-10-4. It’s crazy-making. I wander around muttering to myself and scaring the pets and kids.

Because I’m a person who is easily confused by information overload, I had to break it down into baby steps. And because I’m a person who likes to share, here is a super-simplified guide to fertilizing your veggies. I’m not saying this is perfect, but I can get my head around it and that’s a great place to start.

The basic components of fertilizer are nitrogen (N), phosphorus (P) and potassium (K). There are also secondary nutrients like calcium, magnesium and sulphur, but I’m not even going to go there. Dealing with why “potassium,” which clearly begins with the letter “P” is labeled “K” is confusing enough.

Anyway, the letters N-P-K match those mysterious numbers on the front of fertilizer packages, corresponding to the ratio of the nutrients in the package. So 5-5-5 is equal doses of nitrogen, phosphorous and potassium; 6-10-4 gives a smidge more nitrogen, a hefty extra load of phosphorous, and so on.

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Here’s What I’ve Figured Out

1. Nitrogen Encourages New Growth

Be careful with your nitrogen use, though. Use too much and you might end up with lots of new leaves but not so many flowers or fruit. Time your application of fertilizer carefully; you don’t want a bunch of delicate new leaves when there’s a chance of frost.

2. Phosphorus Supports Root Growth and Flower/Seed Production

How much phosphorus your plants can eat up is affected by your soil pH. (We’ll get to pH later.) Most veggies need a soil pH of 6.5 to 6.8, with berries preferring a bit more acidic soil. Add lots of organic matter—think “poop”—to help your plants soak up the added phosphorous.

3. Potassium Encourages Plant Health and Disease Resistance

And that’s pretty much all I have to say about that. Mostly, plants do OK with potassium, it’s the nitrogen and phosphorous you have to watch.

4. Soil pH is Key

All the super-fertilizers in the world won’t do a bit of good if your soil pH isn’t up to par. Most plants like a soil pH around 6 to 7. Get one of those spike-type soil testers and check yours out. You can add lime or wood ash to raise the pH or ammonium sulfate to lower it, but do this incrementally and slowly. Better yet, churn a bunch of good compost into your soil and the pH should adjust naturally.

Back To the Fertilizer Dilemma

So I’m still stuck with two questions: What to use? When to use it?

There’s loads and loads of info about this all over the ’net, but here’s what I’m doing this year:

  • At planting time stir in a fistful of 5-5-5 into the soil where I’m putting my seeds or transplants.
  • About two weeks later sprinkle a little more 5-5-5 and water it in.
  • Once the plants have some decent growth, I either keep up with the 5-5-5 (especially for plants like lettuce and kale where the leaf is the food) or adjust based on plant type to something with a bit more phosphorous.

You can make yourself nuts getting super-specific with fertilizer applications, and I am sure that’s where I will end up: rambling on to anyone who will listen about how I made my own fish emulsion in the bathroom sink and wandering about with bits of bone meal in my hair. But I’m a firm believer in baby steps, and right now, memorizing the meaning and purpose of NPK is about all I can handle.

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