Problem Identifier / Phosphorus Deficiency in Plants

How to Fix A Phosphorus Deficiency in Plants

Phosphorus Deficiency Jalapeno Leaves
Phosphorus deficiency on the leaves of a jalapeño plant.

There are 17 nutrients required by plants for health and growth including phosphorus. Phosphorus is important because it enables the conversion of nutrients into building blocks the plants can use to achieve growth. Most fertilizers contain three key nutrients including phosphorus. Phosphorus is critical for enlargement and division, photosynthesis, and energy transfer and storage.

Cannabis plants require phosphorus during flowering to produce buds. Phosphorus is important from seedling growth until the plant reaches maturity. Phosphorus stimulates certain growth factors, root development, provides strength for the stems and stalks, improves the formation of flowers, and increases the resistance to diseases. Phosphorus is necessary for the overall vigor and health of all different types of plants.

How Does a Phosphorus Deficiency Affect the Quality of Your Plant?

A phosphorus deficiency in plants affects the quality of the older and lower leaves. The leaves become a darker yellow or green with large bronze, brown or slightly blue splotches or spots. The leaves curl and thicken with a stiff feel. The plant stems may turn bright purple or red. The first sign is usually the darkening of the older leaves.

The leaves sometimes acquire a bronze or bluish tinge with a downward curl. Purplish, bronze or dark grey splotches can then appear. The stems often become purplish or red. A phosphorus deficiency in plants is often seen along with a calcium deficiency since these nutrients interact within the plant.

Phosphorus Deficiency Symptoms in Plants

Phosphorus Deficiency Rapeseed
Phosphorus deficiency and red leaves in a rapeseed plant.

The most common phosphorus deficiency symptoms include:

  • Affects older and lower leaves
  • Bright red stems
  • Leaves darken becoming gray, blue or dark green
  • Leaves become shiny with yellow areas
  • Leaves thicken becoming stiff and dry
  • Sometimes the leaves turn purple or red

A phosphorus deficiency usually impacts the older leaves first. Sometimes the stems are not affected, but in some cases the only symptom of the deficiency is bright red stems. The leaves start to darken, turning a grayish, blue or dark green. Sometimes the leaves look shiny. If the phosphorus deficiency progresses, parts of the leaves will become yellow.

A phosphorus deficiency often leads to issues with the pH balance or deficiencies of other nutrients. If the leaves are turning yellow, the deficiency has already progressed past the beginning stages. At this point, brown, purple or bronze splotches or spots appear on the leaves. The leaves become thicker with a stiff and dry feel. If the phosphorus deficiency is not treated, the stems can turn purple or red.

Due to the interaction of calcium and phosphorus within the plant, a calcium deficiency is also likely.

Possible Confusion with Other Symptoms

What Causes a Phosphorus Deficiency in Plants?

Phosphorus Deficiency Cannabis
Phosphorus deficiency in a cannabis plant.

The most common causes of a phosphorus deficiency in plants include:

  • Cold weather
  • Excessive rainfall
  • Acidic soil
  • Soil compaction
  • Injury from herbicide
  • Pressure from insects
  • Poor soil health

Excessive rainfall and cold weather can temporarily cause a phosphorus deficiency in plants. This is because the phosphorus is leaching out of the soil. If the soil is acidic, the plants can have difficulty absorbing phosphorus even when plenty of the nutrient is available. If the issue is due to cold weather, the deficiency should correct itself once the soil becomes warmer.

The additional causes include compaction of the soil, the pressure from insects, injuries from herbicides and poor soil health.

How to Fix a Phosphorus Deficiency in Plants

When the pH at the plant’s roots is not in the correct range, the result can be a phosphorus deficiency. This is because the roots are no longer able to absorb phosphorus. The ideal pH range for most plants is between 5.5 and 6.2. Check the pH level at the root zone. If it is too high or low, the systems should be thoroughly flushed using pH water containing phosphorus in addition to other nutrients.

Any nutrient salts impacting phosphorus absorption will be removed to correct the pH range. Even if everything else is ideal, a phosphorus deficiency can occur due to overwatering or compact and wet soil. Major temperature swings and temperatures below 60 degrees Fahrenheit can result in a phosphorus deficiency by impacting root absorption.

Phosphorus Deficiency Pepper Plant
Phosphorus deficiency on a pepper plant.

The correct balance of nutrients is critical to help ensure the health of the plants. If there are too many nutrient salts in the growing medium, the reservoir should be changed. Increasing the percentage of phosphorus when feeding the plants can often resolve the issue. Plants grown under either direct sunlight or extremely high-powered lights require additional phosphorus.

Check the plant for root issues because this can result in a phosphorus deficiency. The deficiency can be corrected by using one or more of the following solutions:

  • Make pH adjustment
  • Flush plants with pH water and nutrients containing phosphorus
  • Do not overwater plants
  • Ensure the temperature is correct
  • Provide plants with the correct nutrient ratio
  • Change out the reservoir
  • Provide additional phosphorus for plants grown under high-powered lights
  • Correct root issues
  • Closely observe plants to ensure the deficient has been corrected

How Long Does It Take for a Plant to Recover from a Phosphorus Deficiency?

Plants should recover from a phosphorus deficiency within one week. Irreparably damaged leaves will most likely not become green again, but the symptoms of the deficiency should disappear.

Defeat Pests, Mold and Mildew… NATURALLY!

Like it? Share it!