Overwatering Watering issues are generally the most common cause of yellowing leaves. When your plants are overwatered, the performance and vigor decrease. Oxygen is being pushed out of the soil, and the roots are simply “under aired” and suffocating. With little air, the roots will begin to drown and rot.
Yellow Leaves + Fading to Green + or Bright Yellow =
These symptoms together mean that your plant is overwatered. Usually lower leaves drop first, although the whole plant may be affected. The solution = repot (to remove soaked soil) and water less, or let soil dry out and water less.
"Excessive watering can suffocate a plant's roots," Blank says. "This causes root rot, which prevents the plant from absorbing nutrients properly and results in yellow leaves. Underwatering can cause dehydration and nutrient deficiencies, leading to yellowing leaves."
A yellow leaf has lost its chlorophyll (pigment) and it can't turn green again even after you correct the problem. Don't worry, if the plant regains its health, it's possible that new leaves will fill in during the next growing season. Growing plants is always a matter of patience.
Plants need light, but too much of a good thing can affect your plant's health and cause leaves to turn yellow. Sunburn may cause dark burn-like spots on leaves or can cause full yellowing of leaves receiving too much sun.
Warning: Never cut off yellow leaves!
Whatever the cause, the first thing NOT to do is cut off those yellow leaves. If you do trim yellowing leaves, you're cutting off your plant's temporary life support! Until you find out why and fix what's wrong, put down the snips.
Over-fertilizing. People often use too much fertilizer to make their plants grow faster. The excess salt in the soil from too much fertilizer “burns” the leaves causing them to turn yellow. In the case of houseplants, change the soil or leach it with large amounts of water to correct the balance.
Nitrogen deficiency causes mostly older leaves to yellow. With limited nitrogen, a shrub or tree will send what nutrients are available to support new leaf growth. As a result, older foliage gets fewer (or even no) nutrients.
Nutritional problems
Yellowing of the areas between the veins (interveinal chlorosis) is usually indicative of manganese, iron or magnesium deficiency. Iron deficiency affects the youngest leaves first, whereas the symptoms of manganese and magnesium deficiency tend to start in the older leaves.
Key indicators: Yellow leaves, parched soil, and lack of growth. Leaves might also feel dry and brittle to the touch and look droopy. Remedy: Good old H2O will fix the problem. Prevent it in the future with consistent watering; add a layer of mulch around outdoor plants in dry areas.
Q. How often should plants be watered? Water once or twice per week, using enough water to moisten the soil to a depth of about 6 inches each time. It's okay if the soil's surface dries out between waterings, but the soil beneath should remain moist.
When plants have too little water, leaves turn brown and wilt. This also occurs when plants have too much water. The biggest difference between the two is that too little water will result in your plant's leaves feeling dry and crispy to the touch while too much water results in soft and limp leaves.
Signs of Overwatering
When a plant is first becoming overwatered, leaves turn yellow. If soil doesn't have a chance to dry out before you water again, leaves start to wilt. When overwatering is the problem, wilted leaves are soft and limp. (If too little water is the issue, wilted leaves are dry and crispy.)
You may see some yellow leaves and some leaf drops in late summer. A few yellow leaves falling in summer doesn't automatically mean your tree is in trouble. For example, a tree may drop insect-damaged or diseased leaves if they no longer produce food energy for the tree by photosynthesizing.
Apply a liquid fertilizer containing iron or Liquid Iron, though it may leave a rusty residue on the leaves. This is only a temporary solution. Adjusting the soil pH is another option. Applying sulfur will lower the pH, allowing the iron to be more available to the root system.
Identification. Slow growth and uniform yellowing of older leaves are usually the first symptoms of nitrogen (N) deficiency. Nitrogen-deficient plants produce smaller than normal fruit, leaves, and shoots and these can develop later than normal.
Magnesium Deficiency
Signs: Leaves yellow with white stripes along still green veins. It usually first appears on lower limbs. Treatment: Add compost or fertilizer rich in magnesium sulfate (commonly known as Epsom salts) to the soil.
Signs of fertilizer burn include dry, brown leaf tips and edges. White crust or deposits on soil, pot surfaces, leaves and stems indicate build up of harmful salts. Stunted growth and sudden wilting are more serious symptoms.
Identification. Symptoms of excess nitrogen include thickened and sometimes cupped leaves with atypically deep green color. Overfertilization can cause leaves to turn brown, gray, dark green, or yellow at margins and tips or overall. Affected foliage may wilt temporarily or die and drop prematurely.
If it feels soft and limp, it is overwatered. Yellowing leaves: Usually accompanied by new growth falling, yellow leaves are an indication of overwatering. However, yellow, curling lower leaves can also be an indication of underwatering. Check the soil for moisture to decide which it may be.
The most common reason that plants' leaves turn yellow is because of moisture stress, which can be from either over watering or under watering. If you have a plant that has yellow leaves, check the soil in the pot to see if the soil is dry.