Yellow Leaves and Nutrient Deficiencies

“Why are my plant’s leaves yellow?”

If you’re like most gardeners, you’ve faced this befuddling question before. Leaf yellowing — known as “chlorosis” in the world of science — has many potential causes. But one of the most common is undernourishment.

For healthy development, plants require 16 different micronutrients and macronutrients. And if they don’t get them or if proportions are imbalanced, leaves may start to look strange, become more susceptible to disease, and slow (or even stop) their growth — decreasing yields.

Other Causes of Discoloration and Disfigurement

Nutrition isn’t the only reason a plant’s leaves may look unusual. Here are a few other common causes.

Pests and Plant Diseases
It’s wise to watch for garden pests. Because bad bugs not only damage and stress plants — they also often introduce the following types of plant diseases, which bring additional harm:

Bacteria – Bacterial diseases can cause wilting and spotting.
Fungi – Some leaf fungi mimic certain symptoms of nutrient deficiencies, including yellowing and necrosis.
Virus – If you see blotchy or patchy yellowing on your leaves, a virus may be the responsible (especially if the discoloration is accompanied by disfigured growth).

Symptoms of Plant Nutrient Deficiencies

Before you can address a deficiency, you’ve got to be able to figure out which nutrient your plant needs. So here are a few ways a plant may show you it’s missing something important:

Boron – Young leaves turn light green and may be disfigured.
Calcium – Leaves are disfigured and may wilt or show signs of necrosis (i.e., death of plant tissue).
Copper – Leaves may be limp and/or curled.
Iron – New leaves turn a pale, yellow color between green leaf veins (this is known as interveinal chlorosis).
Magnesium – Leaves show spotting and yellowing between green leaf veins. Outer edges of leaves may pucker or curl.
Manganese – Younger leaves turn yellow between veins (giving them a net-like look) and may develop dead spots.
Molybdenum – Older leaves yellow. Remaining leaves turn light green. All leaves may become distorted and narrow.
Nitrogen – Older leaves and veins turn a pale, yellow color. Other leaves turn light green and stay smaller than normal.
Phosphorus – Leaves looks stunted and turn dark green or even a deep purple color (almost black for some plants). Leaf tips may look burnt.
Potassium – Older, lower leaves show marginal necrosis, even looking scorched around the edges. Leaves also yellow on edges and between veins.
Sulfur – New leaves yellow and leaf veins lighten while older leaves remain green. (May be confused for a nitrogen deficiency.)
Zinc – New leaves yellow and may develop necrosis between veins.

How to Fix Nutrient Deficiencies

The best way to solve deficiencies is to avoid them in the first place by giving your plants the nutrients they need.

Tower Tip: Even if you’re providing the essentials, a high or low pH may keep plants from absorbing or processing them. Most plants access nutrients best when pH is around 6.5. So measure your levels every few weeks and adjust as necessary.

Aphids

Typically green, yellow or black in color, aphids are small, sap-sucking, soft-bodied insects. If you have aphids, you’ll likely find them on plant stems and leaf undersides. There they feed on tender, young growth, causing plants to appear puckered or deformed. You can also detect aphids by the presence of honeydew, a sugar-rich, sticky liquid they secrete.

Beetles

Spotted, striped and banded, orange, yellow and brown—bad beetles come in many forms. Common species include the cucumber beetle, flea beetle, Mexican bean beetle and Japanese beetle. They all typically feed on plant leaves and flowers. One good beetle you want to have around, however, is the ladybug.

Caterpillars

Caterpillars are the soft-bodied, segmented larvae of moths and butterflies. Their color varies by species (common species include cabbage loopers and tomato fruitworms). Generally, caterpillars feed on either plant leaves or fruit. In addition to holes in foliage and fruit, black specks (fecal matter) on your Tower Garden reservoir lid are signs of a caterpillar infestation.

Leafhoppers

Leafhoppers are wedge-shaped and often light green in color. You can detect them by stippling on the top of plant leaves, which looks like white or pale yellow spots. In addition to eating plant leaves, leafhoppers are known to transmit viral plant diseases.

Leaf Miners

Leaf miners are small gray flies whose pale, tiny larvae feed between plant leaf surfaces, causing winding trails throughout the leaf tissue. These trails often merge together to form light-colored, dead areas on the leaves. Leaf miners can damage fruit-bearing plants. But they render greens inedible since the larvae are inside plant leaves.

Spider Mites

As sap-sucking insects, spider mites stunt plant growth and sometimes even kill plants. Spider mite damage appears as pale yellow spots ranging in size from specks to large areas on the tops of the leaves.

Scales

Scales vary in color and appearance, but they generally look like small bumps on plant stems, leaves and fruit. Scales feed on plant sap, weakening plants and often causing leaves to yellow and die. They also secrete honeydew, like aphids.

Shield Bugs

Commonly known as stink bugs, these sap-sucking insects have shield-shaped bodies and come in many different colors. Most are bad for your garden, as they feed on plant foliage and fruit, damaging crop production. But one shield bug—the spined soldier bug, which has very distinct and pointy “shoulders”—can actually help control pest populations.

Thrips

Adult thrips are tiny, pale-yellow, sap-sucking insects with elongated bodies and fringed wings. They tend to hide in the centers of flowers and scatter when the bloom is disturbed. Thrip damage appears as coarse stippling on the leaf surface. Large populations of thrips cause serious plant injury, which results in a silvery or scratchy appearance on leaf surfaces.

Whiteflies

The whitefly is a voracious sap-sucking insect that causes stunted plant growth, leaf yellowing and reduced yields. With slender white bodies and wings, whiteflies tend to congregate in great numbers on the undersides of leaves to feed, taking flight when disturbed. Whiteflies also secrete honeydew, which encourages mold growth.

3 ways to control your pests without the use of Pestecide

DIY Spray for Virtually All Pests
Credit for this formula goes to Rodale’s Organic Life. It’s effective for most garden pests and may even help deter rodents and deer. Plus, you likely already have the ingredients.

Here’s how to make it:
Chop, grind or liquefy 1 garlic bulb and 1 small onion.
Add 1 teaspoon of powdered cayenne pepper, 1 quart of water, and mix.
Steep 1 hour, then strain through cheesecloth, and add 1 tablespoon of liquid dish soap (such as pure castile liquid soap — not dishwashing detergent) to the strained liquid; mix well.
To avoid skin and eye irritation, wear rubber gloves and keep the mixture away from your eyes and nose when preparing and applying it. Refrigerate any remaining spray for up to 1 week in a covered container.

Insecticidal Soap + Neem Oil Spray for Most Insects
This powerful combination is widely used among organic gardeners for aphids, mites, thrips, whiteflies and other small, soft-bodied insects.

Hat tip to Future Growing, LLC for the following ratio:
1 tablespoon of insecticidal soap
1 tablespoon of neem oil
1 gallon of water
After spraying, discard any remaining mixture and clean your applicator.

Bacillus Thuringiensis Spray for Caterpillars
Bacillus thuringiensis (Thuricide) is the “go-to” natural spray for caterpillars. You can pick some up online or in your local garden center. Mix and apply it according to the product label directions.

Tower Tip: If you shop for a pest control solution at a local garden center, keep in mind that organic-approved sprays will feature the OMRI seal of approval.