Secret Life of Plants 4: Plant Nutrition

A customer recently asked me: “Can you suggest what type of plant food I can use for my Haworthia collection?”

That question struck a chord because I used to do research on nitrogen utilization in plants, and I realized it might be useful to share a deeper look at plant nutrition and how it relates to succulent cultivation. Over the years, my views on fertilizing succulents—and fertilizing in general—have evolved significantly.

Plant Nutrition Basics

Plant nutrition is fascinating on many levels. First, humans are entirely dependent on plants for our own nutrition. Second, plants themselves build their bodies using the energy of the sun to convert carbon dioxide into sugars, which they store and use as food. (For more on this process, see my earlier blog on photosynthesis: Secret Life of Plants 2: Photosynthesis).

About 90% of a plant's dry biomass is made of carbon, hydrogen, and oxygen—derived directly from sugars produced in photosynthesis. The other ~10% consists of essential mineral elements that plants absorb from soil or growing media.

Experiments using defined media showed that plants require a balanced supply of nutrients to grow, reproduce, and defend against stress. These nutrients fall into two broad categories:

• Macronutrients: Needed in larger amounts.

• Micronutrients: Needed in smaller amounts but no less essential.

Here’s a summary of the most important ones:

Without these nutrients in the right balance, plants become weak and vulnerable.

Fertilization Through History

For most of human history, farmers and gardeners didn’t have easy access to “plant food” in a bag. Instead, they relied on manure, compost, ash, bone meal, and other organic materials to replenish soil fertility.

The Haber-Bosch Revolution

In the early 1900s, the Haber-Bosch process was discovered. It allowed atmospheric nitrogen gas to be converted into cheap, synthetic fertilizer at industrial scale. This innovation dramatically increased global food production, enabling the human population to rise from about 1.6 billion in 1900 to over 8 billion today.

But this shift also tied farming more closely to industrial inputs, moving away from natural nutrient cycles.

The Green Revolution

By the 1940s, another problem emerged: excessive nitrogen fertilization often caused plants to grow tall and weak, making cereal crops like wheat and rice prone to lodging (falling over). Scientists responded by breeding shorter, sturdier “dwarf” varieties. This became the Green Revolution, which greatly improved yields and helped feed the world.

Modern Fertilizers

Modern fertilizers, such as Miracle-Gro, are typically blends of mineral salts that supply readily available N-P-K plus micronutrients for rapid uptake. Slow-release products like Osmocote provide nutrients gradually over time.

A common misconception is that fertilization is simple—plants just take what they need, and the rest leaches out. In reality, different nutrients are absorbed at different rates. For example:

• Nitrogen is easily absorbed, often in excess.

• Calcium is much harder to absorb, so high nitrogen can actually cause calcium deficiency.

This imbalance leads to problems like:

• Tip burn in lettuce.

• Blossom end rot in tomatoes.

(As a side note: this season, I had my first tomato crop without end rot—because I skipped synthetic fertilizers and relied solely on manure at planting. The plants grew slower but stronger.)

Excessive fertilizer also leads to weak, pest-prone growth—a problem that’s as true for succulents as it is for vegetables.

Fertilizing Succulents

So, what’s the best fertilizer for succulents?

Simple answer: very dilute, very infrequent—if at all.

The key is remembering that growth rate matters. Corn grows fast, Haworthia grow very slowly. Their nutrient needs are correspondingly modest.

When I first started growing succulents, I used Miracle-Gro. The results were… dramatic. Lithops literally split open from too much growth. A treasured Tylecodon grew long, weak stems that toppled over. In short: succulents are just as susceptible to nitrogen-induced lodging as pre-Green Revolution cereals.

Over decades of growing, I’ve found that synthetic fertilizers often do more harm than good, encouraging weak, disease-prone growth.

My Fertilizer Strategy Today

Because my growing substrate is mostly pumice (nutrient-free), I do add some nutrients. My current approach is:

• Mix a small amount of Osmocote into the soil at repotting.

• Add decomposed granite (DG), which provides a slow, natural supply of many minerals.

A Caltrans study found that “DG substrates have generally adequate levels of non-N nutrients for plant growth” (source).

I’ve moved away from routine synthetic fertilizer use—not just for succulents but for most of my plants.

Practical Advice for Succulent Growers

• Favor natural nutrient sources like decomposed granite.

• Use a small amount of slow-release fertilizer (e.g., Osmocote) when repotting.

• If you must use synthetic fertilizers:

  • Make sure they include calcium and micronutrients.

  • Dilute them to at least ¼ the recommended strength.

  • Apply no more than once per year.

Succulents thrive on restraint—nutritionally and otherwise. A little goes a long way.

Don’t Forget About pH Balance

One final piece of the plant nutrition puzzle is pH balance. Water quality can make a big difference in nutrient availability. Tap water—and even greenhouse irrigation water—often has a high, alkaline pH. This excess alkalinity can reduce nutrient uptake, leaving plants with deficiencies even when nutrients are present.

For this reason, I recommend occasionally watering with pH-adjusted water around pH 6.0. You can easily measure and adjust water pH with kits available on Amazon or at hydroponic supply stores. To lower pH, growers commonly use phosphoric acid (sold in pH up/down kits), vinegar, or organic acids like Earth Juice. A small adjustment goes a long way toward keeping nutrients available to your succulents.