Discover the signs of NPK deficiency and toxicity in your houseplants. Too much or not enough macronutrients (Nitrogen/phosphorus/potassium) found in complete fertilizers will cause problems for your houseplant.
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Today, I’m going to talk about the signs of NPK deficiency and toxicity. I have other videos on NPK, which I’ll link below, along with any related videos that may be helpful.
Plants need nutrients for healthy growth and productivity. There are 17 essential elements required for plant growth, categorized into macronutrients and micronutrients. Today, we’re focusing on the “big three” macronutrients that appear on fertilizer bags as numbers like 10-10-10 or 20-20-20—those are NPK: Nitrogen, Phosphorus, and Potassium. Plants need these in large amounts for proper development.
If there’s a deficiency in any of these essential elements, your plant’s vegetative or reproductive cycle will be interrupted, leading to visible deficiency symptoms. These usually show up in the leaves.
🔍 Nitrogen (N)
Nitrogen greens up your plants. For example, a healthy Ficus benjamina will have lush green leaves. A nitrogen deficiency results in stunted growth, yellowing of older leaves first (then younger leaves), and early leaf drop.
Excess nitrogen leads to overly dark green leaves, especially in plants that are usually light green. It can also cause bud drop, lesions on stems and leaves, and even browning along stems and roots. Over-fertilizing—especially with chemical fertilizers like anything over 10-10-10—can quickly lead to nitrogen toxicity.
🔍 Phosphorus (P)
Phosphorus deficiency leads to stunted growth, purple coloration on older leaves, dark green discoloration, and delayed flowering or fruiting. A flowering plant that stops blooming may be lacking phosphorus.
Too much phosphorus can cause deficiencies in iron and zinc, as all essential elements need to work in concert.
🔍 Potassium (K)
Potassium deficiency shows up as brown leaf tips and marginal burn. If you’ve ruled out low humidity, improper watering, or pH imbalance, potassium may be the issue. Symptoms appear first on mature leaves and lower leaves may yellow. Potassium deficiency also weakens plant growth and slows development.
A complete fertilizer contains all three macronutrients—NPK—in balanced amounts. If you’re seeing signs of deficiency, applying a balanced fertilizer will often correct the issue.
I also have a playlist on fertilizing that you can check out. Thanks for stopping by! Leave a comment with indoor gardening topics you’d like to see covered. Don’t forget to like, comment, subscribe, share, and hit the bell for notifications!
Signs of NPK Deficiency and Toxicity in Houseplants
What are NPK nutrients?
NPK stands for Nitrogen, Phosphorus, and Potassium—three essential macronutrients that plants need in large quantities for healthy growth and development.
What are signs of nitrogen deficiency in houseplants?
Yellowing of older leaves, stunted growth, and premature leaf drop are common signs of nitrogen deficiency in houseplants.
How can you tell if a plant has too much nitrogen?
Signs of nitrogen toxicity include overly dark green leaves, stunted growth, bud drop, lesions on leaves and stems, and browning along stems and roots.
What are the symptoms of phosphorus deficiency?
Phosphorus deficiency may cause stunted growth, purplish coloring on older leaves, delayed flowering, and dark green discolorations.
What happens when a plant lacks potassium?
Potassium deficiency leads to brown leaf tips, marginal burning, yellowing of lower leaves, and weakened, slowed growth.
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Organic Fertilizer: Espoma Houseplant food liquid: https://amzn.to/3TstMfM