Crash course in fertilizers: Part 2

Plants need calcium. So do we. Lemons are a good source of this mineral. Have you ever dried lemon slices into chips? Better than corn chips! 

Last week I introduced the Big Three — nitrogen (N), phosphorus (P) and potassium (K) — as part of our crash course in fertilizers. Today we’ll cover the secondary elements: calcium, magnesium and sulfur, plus the rest of the supporting cast.

While N, P and K might be garden superheroes, without the secondary  elements, they couldn’t do their job. The roles these micro-nutrients play are as essential to growth as those of N, P and K. So let’s take a look ...

First, meet calcium

Most of us are familiar with calcium as the element associated with healthy bones, teeth and shells. “Drink your milk!” our moms told us. But milk isn’t the only dietary pit stop to fill up on calcium.

Here are a few non-milk sources of calcium: seafood, such as canned salmon (with bones), dark green leafy veggies (kale, collards, bok choy, turnip greens), beans, black-eyed peas, almonds and dried figs — even lemons (more on the later).

What does calcium look like? In its raw state, calcium is a soft, gray earth metal. Interesting to know that it’s the most abundant metal by mass in many animals.

In plants, calcium concentrates primarily in leaves. There it builds cell walls and, like a gatekeeper, it regulates the availability of other nutrients. In the garden, calcium deficiencies appear in many ways —  for example, as blossom-end rot on tomato and squash plants.

Sources of calcium include dolomite lime, wood ashes, compost and crushed oyster shells.

Say hello to magnesium

Simply put, photosynthesis would be impossible without magnesium. It would be like being in your kitchen, with cabinets and a fridge stocked with ingredients, but you can’t cook.

Magnesium helps plants use other nutrients such as nitrogen, phosphorus and sulfur. A lack of magnesium appears as subtle red flags. Literally — as a red, yellow or even purpling of leaf tissue between veins, which remain green. But don’t jump to conclusions. What may appear as a phosphorus deficiency may be a magnesium deficiency that results in a plant’s inability to absorb phosphorus. Fun stuff. Gardeners must be Sherlock Holmes.

Meet Sir Sulfur

Sulfur is yet another secondary element critical for helping plants produce proteins and enzymes. Unlike many other elements, though, sulfur isn’t readily held by soil particles. Which means it tends to leach away past the root zone where plants can’t reach it.

Your first clue that plants, such as rhododendrons and cabbage, are lacking sulfur is chlorosis, the yellowing of leaves. But unlike a nitrogen deficiency, the entire leaf doesn’t dry and become brittle as when lacking nitrogen. 

There’s a story about a little old lady who grows prizewinning roses by sprinkling the ground beneath them with Epsom salts. Epsom salts are often revered as the fix-all in the garden. Should we follow her lead? Not necessarily. Epsom salts are simply magnesium sulfate, a source of the plant foods magnesium and sulfur. If your soil lacks either, Epsom salts will give your plants a boost; if not, the effect will be slight to nil.

You can buy elemental sulfur, which looks like yellow split peas (common practice for rhododendron growers who want to lower the soil’s pH at the same time). But to increase your science knowledge bank, know that soils actually obtain sulfur from three sources:

1. Airborne particles

2. Weathering of minerals in soils

3. Microbial activity

Finally, there are nine nutritional elements that plants need in tiny amounts. Those are oxygen, carbon and hydrogen, which come from air. That leaves zinc, boron, manganese, iron, copper and molybdenum, which, lucky for us, are available in manures, compost and seaweed.

While I won’t go into minute details here, just remember that you can’t, nor should you, simply add chemical fertilizers with high N:P:K numbers on your garden or lawn. Plants, like us, do best with a varied diet. 

Back to lemons, as promised. Winter in Alaska is citrus season. Lemons and oranges, especially. Lemons are a good source of calcium, and are considered one of the super-foods. When you find organic lemons and oranges, celebrate their zest by processing them into a munchable, healthy snack: citrus chips!

How to make citrus chips, step by step:

1. Dust off your dehydrator.

2: Rinse off lemons and/or oranges.

3. Cut slices 1/8 to 1/4 inch thick. Don’t worry about seeds.

4. Place on racks, without overlapping slices, and dry until totally dry.

5. Store in airtight containers.

To eat, crunch on them as plain chips, steep in tea, add to soups or dip into vanilla yogurt or chocolate.

Let me know how it goes, or if you have a favorite sauce or use for citrus chips.

While your slices are drying, get your seed-starting underway:

Plants that would be good to start now include Brussels sprouts, celery, lobelia, parsley and sweet alyssum.


Get Marion’s free Photo Tips PDF, a collection of her favorite photography tips, on her blog at Connect with Marion: Facebook and Instagram or send an email to Marion at



(0) comments

Welcome to the discussion.

Keep it Clean. Please avoid obscene, vulgar, lewd, racist or sexually-oriented language.
Don't Threaten. Threats of harming another person will not be tolerated.
Be Truthful. Don't knowingly lie about anyone or anything.
Be Nice. No racism, sexism or any sort of -ism that is degrading to another person.
Be Proactive. Use the 'Report' link on each comment to let us know of abusive posts.
Share with Us. We'd love to hear eyewitness accounts, the history behind an article.