Plants Eat Food, pt2 – Secondary Nutrients

Secondary only refers to the quantity, not the importance of the nutrients. These are just as important! Much like how we’re skipping over oxygen and carbon because they’re readily abundant, these fall on the other end of the spectrum.

Please check out Part 1 – about Nitrogen, Phosphorus, and Potassium!
Then follow along next week for the Trace Elements in part 3.


The only nutrients needed more than Calcium are Potassium and Nitrogen. 

Calcium helps build the cell walls of the plant. This is both good and bad: once the calcium is fixed in place, it can’t be moved. Calcium can’t be taken from older plant cells. Calcium helps regulate quite a few things, alongside building cell walls. It reduces cell acidity, regulated soil acidity and salt levels, helps remove carbohydrates, and helps water penetration.

Excess calcium isn’t toxic, but will instead cause problems with the uptake of other minerals. High levels of other cations, such as magnesium or potassium, will reduce calcium uptake for some plants. To further this problem, some of the more common ways in which calcium occurs (calcium carbonate) can’t be used by plants and doesn’t readily leech into the soil. 

Because calcium can’t move once it’s fixed, it’s better to add calcium regularly throughout the growing season. Additionally, some calcium sources may change soil ph. Pick your calcium source carefully!

Depending on where the water comes from, your water may also supply sufficient calcium.

“As a general rule, water coming from deep wells or most non-coastal regions of North America has sufficient calcium for normal crop growth, while water from a shallow well, coastal region, rain, lake, river or pond generally has insufficient calcium levels.”

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A lack of calcium can present in a variety of ways. The tips and edges of new leaves might show necrosis, roots may grow highly branched and very short, bulbs and fruit may be disfigured. Just keep in mind that new growth is going to show the problem – old plant cells that already have calcium won’t lose it.

Ca : Quick Facts

  • Builds cell walls and regulates acidity
  • Non-mobile, so keep adding it if plants need it
  • Problems show up in new growth


Magnesium is complicated. 

At its base, it’s the center of the chlorophyll molecule in plant tissue. It’s pretty serious business. Magnesium also works to activate some enzymes in the plant (enzyme: a substance that builds/modifies/breaks down other compounds).

Magnesium has a very complex web of interactions in nature – from the minerals it comes from, the clays it settles on, to all the different ways it reacts. Magnesium levels can differ from area to area. However, because of how it reacts with acidic soil, be wary of any soil below a 5.5 ph (such as sandy soil, or properly grown blueberries). There’s some argument that magnesium needs to be balanced against Calcium. Some studies have shown that this isn’t the case. All I know is – it’s better to have it than not. Make sure you have both before you try any wild mixes. 

Magnesium can be a tough rock to come by. In large applications, it can come from specialized fertilizers or dolomitic limestone. For smaller applications, it may be better to find a fertilizer that includes ‘trace elements’ or something of the sort.

Lack of magnesium can lead to stunted plant growth, or poor growth overall. Because of how mobile it is, problems will show up first in the older leaves. Typically, because it’s a lack of chlorophyll, the leaves will stop being as green. Leaves will turn yellow (between the veins, which are still green at first) and eventually develop brown spots. However, just because your leaves are turning yellow doesn’t necessarily mean a magnesium deficiency is to blame. There are plenty of other diseases and pests that can cause similar problems.

Mg : Quick Facts

  • Wonderfully interactive
  • Terrifically complex interactions


Sulfur’s a fun one. Ever hear of acid rain being beneficial?

Sulfur is needed for the formation of many enzymes and proteins in the plant – including the all-important chlorophyll.. Plants don’t need much sulfur, compared to most things, but a deficiency can cause some serious problems. It’s just as necessary as phosphorus (or nitrogen!).

Sulfur and nitrogen balance each other, to some extent. Too much of one or the other can cause problems. Without sulfur, plants can’t use the other nutrients effectively. It’s also necessary for some of those wonderful garlic and onion flavors, and some seed oils. Sulfur protects you from vampires, but smells like devils and deviled eggs. 

Sulfur is pretty mobile in soil, and comes from some odd places. You can add it to the soil directly, or through manure that leeches into the soil over time. The long and short of it is, it’s difficult to have excess sulfur (to the point of sulfur toxicity), instead the plant will start having problems with nitrogen uptake. 

The main source of sulfur for crops, at least according to some, was from acid rain and burning fuels. Dead plant matter may be a source too, as are sulfur buildups up on deep gypsum deposits. You can even add epsom salts to your water-soluble fertilizer (about 3oz per 100 gallons) to get sufficient levels. It’ll also come from fertilizers, manure, and pesticides – look for something with at least 25ppm of sulfur.

Deficiency of sulfur will look like a deficiency of nitrogen: yellowing of the leaves. However, sulfur deficiencies cause yellowing of the younger leaves, while nitrogen deficiency hits older leaves near the bottom and moves upward. Lack of sulfur over enough time will lead to a chlorotic plant – deficient in chlorophyll, it’ll be overall less green (more yellow) and have stunted growth.

S : Quick Facts

  • The sister element to nitrogen for plants
  • Comes from odd places
  • Deficiency can lead to chlorosis

Thanks for stopping by! I hope you had a pleasant time checking out the plants. If you’re in the mood for more nature, please stay in touch!


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