A houseplant that’s watered correctly and sitting in decent light can still struggle if the soil around its roots has simply run out of nutrients. Potting mix is a fixed, small volume that gets depleted over time, especially with every watering that flushes some of it out through the drainage hole — and the way a plant shows that depletion often points to which specific nutrient is running low.

Why this happens even with regular watering and light

A plant that’s been in the same pot for a year or more without any feeding is very likely nutrient-depleted, regardless of how well you’re managing water and light. See how often to fertilize houseplants for the full routine — this post focuses specifically on recognizing what a deficiency looks like once it’s already showing up.

Nitrogen deficiency

Signs: Pale, yellowing older leaves, starting from the base of the plant and working upward, while new growth stays small and slow. Nitrogen is mobile within the plant, meaning it gets pulled from older leaves to support new growth when supply is short, which is why the oldest leaves show symptoms first.

Fix: A balanced or nitrogen-forward fertilizer, since nitrogen is the nutrient most directly tied to leafy green growth in foliage houseplants like pothos, philodendron, and monstera.

Phosphorus deficiency

Signs: Dark, dull green or slightly purplish leaves, stunted overall growth, and weak or absent flowering in plants that should be blooming. Phosphorus deficiency is less immediately obvious than nitrogen deficiency since the coloring shift is subtler.

Fix: A fertilizer with a higher middle number (the P in NPK) matters more for flowering plants like African violets or peace lilies than for plants grown purely for foliage.

Potassium deficiency

Signs: Yellowing or browning along leaf edges and tips, sometimes with the interior of the leaf staying green — a different pattern from the more general yellowing that nitrogen deficiency causes. Potassium deficiency can also leave a plant more vulnerable to disease and slower to recover from stress overall.

Fix: A balanced fertilizer that includes potassium in reasonable proportion; most all-purpose houseplant fertilizers already cover this without needing a specialty blend.

Iron deficiency

Signs: Yellowing between the veins of new leaves while the veins themselves stay green, a pattern called interveinal chlorosis. This shows up on new growth first, unlike nitrogen deficiency, because iron doesn’t move around the plant as easily once it’s been used.

Fix: An iron supplement or a fertilizer containing chelated iron. Iron deficiency is often tied to soil pH rather than an actual lack of iron in the mix — iron becomes harder for roots to absorb in soil that’s too alkaline, so if a supplement doesn’t help, the soil’s pH may be the real issue.

Magnesium deficiency

Signs: A similar interveinal yellowing pattern to iron deficiency, but typically showing up on older leaves first rather than new growth, sometimes with a reddish or purplish tinge at the leaf edges.

Fix: Some fertilizers include magnesium already; if not, a diluted Epsom salt solution (magnesium sulfate) is a common and effective supplement for houseplants specifically.

Ruling out look-alikes before you treat

Several of these symptoms overlap with problems that have nothing to do with nutrients. Overwatering causes yellowing that can look a lot like nitrogen deficiency — see overwatering vs underwatering houseplants and why are my plants’ leaves turning yellow before assuming a feeding issue. Hard tap water and salt buildup from previous overfeeding can also cause leaf browning that mimics potassium deficiency — flushing the soil with plain water is worth trying before adding more fertilizer on top of an already salt-heavy mix. If a plant is severely rootbound, its roots may simply not have enough soil volume left to draw nutrients from regardless of how well-fed that soil is — see how to tell if a houseplant is root bound.

When soil is the real fix, not fertilizer

If a plant has been in the same mix for a couple of years, the soil itself may have broken down and compacted to the point that feeding alone won’t solve much — see the best soil mix for houseplants and how to repot a houseplant. A plant that’s been showing persistent deficiency symptoms despite regular feeding is often better served by fresh soil at its next repotting than by increasingly aggressive fertilizing.