Cures for Plant Nutrient Deficiencies

Use this quick guide to identify the problems with sick plants in your indoor garden.


Yellow Lower Leaves

Symptoms: Lower leaves turn yellow, shrivel, and may eventually fall off. Plants, especially big ones, normally lose leaves off the bottom as they approach the end of the flowering cycle, but yellowing that moves steadily up the layers of leaves during the vegetative stage indicates a problem. Younger plants are stunted.

Cause: Nitrogen deficiency

Cures: Nitrogen is the nutrient that plants depend on for leaf and stem growth, so it is an essential component of most fertilizers. It is particularly vital during the plants’ vegetative stage (a little less so during flowering). To fix a nitrogen deficiency, first check the label of your fertilizer to be sure that you are using the proper dilution rate—even a small discrepancy could affect your plants. If the dilution rate is correct, your plants may still suffer from nitrogen deficiency if the nutrient solution has a pH below 5.0 or above 7.5. Use organic fertilizers, which are not high in salts, like synthetic plant foods are, as they lower pH. Choose one that’s formulated for the stage your plants are growing through, whether it is vegetative or flowering.

Very Dark New Leaves

Symptoms: New leaves are very dark green. The leaves begin to curl downward and their edges become very dry, looking a little like they’ve been burnt.

Cause: Nitrogen toxicity

Cures: The urge to turbocharge plants often entices inexperienced growers to give them extra nutrients, which can lead to damaging levels of nitrogen. Resist this impulse and instead feed your plants organic fertilizers, which gradually provide nutrients in the form that is best absorbed. Synthetic fertilizers are like steroids for people, stimulating unnatural growth and in many cases leading to toxicity. Thoroughly flush your hydroponic system or the soil with just water before beginning to feed the plants again.

Purplish Leaves and Stems

Symptoms: Stems and leaf veins have a purplish tint. (Plants with naturally purple stems and leaves have a consistent color rather than a changing color from the base to the top.) Plants’ growth is stunted, and they may lose leaves.

Cause: Phosphorus deficiency

Cures: When the temperature of your indoor garden or the nutrient solution falls below 55 degrees Fahrenheit, plants take up less phosphorus than they need. If you’ve determined that the temperature is not the problem, treat your plants to bone meal, an organic supplement that’s rich in phosphorus. Affected leaves do not recover, but the new growth will be healthy.

Yellow or Dead Leaf Tips and Edges

Symptoms: The tips and edges of newly matured leaves have yellow or dead areas. Stems and branches are weak and break easily. Older leaves may appear reddish and curl upward.

Cause: Potassium deficiency

Cures: Excess calcium, sodium, or nitrogen in your nutrient solution prevents plants from absorbing potassium. Those conditions can be the result of using water that is high in minerals (aka, hard water) or that’s been treated with water softeners or synthetic fertilizers. Feed your plants organic nutrients for the right stage of the plants’ growth: Potassium needs are higher during the flowering stage when the need for nitrogen is lower.

Mottled Leaves

Symptoms: New top leaves appear mottled, misshapen, or stunted.

Cause: Calcium deficiency

Cures: When the pH of your nutrient solution falls below 6.0, calcium becomes less water-soluble and plants are not able to absorb it efficiently. Adjust the pH so that it is not too acidic. If the pH is in the right range, use a bone-meal supplement, which is rich in calcium, to increase the supply of the mineral for your plants.

Yellow Older Leaves

Symptoms: The older leaves (lowest on the stem) turn yellow or bright green, starting at their edges, and may even become white while veins remain dark green. The leaves begin to curl upward and eventually drop off.

Cause: Magnesium deficiency

Cures: The pH levels of the nutrient solution must be between 6.0 and 6.5 for plants to absorb magnesium, and plants need appropriate levels of calcium to take up and use magnesium, too. When you need to add supplemental magnesium, Epsom salts (magnesium sulfate) are a widely available source. Bear in mind that leaves afflicted by a magnesium deficiency probably won’t recover, but the yellowing and loss of lower leaves should stop when the problem is corrected.

Bands of Yellow on Leaves

Symptoms: Younger top leaves have yellow between the veins, creating a banded appearance, and they begin to grow closely together in bunches. They may also be gnarled or twisted rather than their normal shape. If the plant is in its flowering stage, the buds may die off.

Cause: Zinc deficiency

Cures: Zinc is vital for plants’ production of chlorophyll and healthy leaf and stem development. As with other minerals, alkaline and acidic conditions (high and low pH) block plants from absorbing zinc effectively. Bone-meal supplements both raise the pH and increase plants’ calcium content, which helps them better absorb zinc.

Brown, Mushy Roots

Symptoms: Plants’ roots are brown and mushy rather than white and firm. Leaves droop and are pale green to yellow.

Cause: Oxygen deficiency

Cures: When plants’ roots are immersed in stagnant water, they become oxygen deprived and develop root rot. Hydroponic systems work best when the nutrient solution is oxygenated with an air pump as it’s delivered to the plants. Soil-grown plants suffer from oxygen deficiency when they are over-watered. Give the soil a chance to dry out between watering and give your plants only the amount of water they can absorb in a few hours. Once a plant suffers from root rot, it’s nearly impossible to rescue it.

Stunted Growth

Symptoms: Stunted growth. Plants take up less water or nutrient solution than normal.

Cause: Carbon dioxide deficiency

Cures: When carbon dioxide levels are low, plants are not able to photosynthesize efficiently and their growth slows. Since you exhale carbon dioxide with every breath, talking to (or at least around) your plants can increase the available carbon dioxide. A fan blowing gently in your grow room refreshes the air around plants and brings them a new supply of carbon dioxide. A fan with outside ventilation is even better. For grow rooms with a high concentration of plants, a carbon dioxide generator helps ensure that there’s always enough.