Irregular yellowing with potential leaf deformities is usually caused either by a pest or a mineral deficiency. If no pests are visible, then this is likely caused by a mineral deficiency, usually calcium or boron. The solution = fertilize once a month, or repot your plant to provide fresh potting soil.
If lower leaves are yellow and a lot of leaves on the plant are pale, light green it is a sign of insufficient nitrogen in the soil. Repotting in fresh soil may perk it up or you can start fertilizing on regular basis. Nitrogen is good for foliage plants or for flowering plants that have yellow leaves and weak growth.
Nitrogen is often the first nutrient that comes to mind as the culprit when leaves turn yellow, but it is not the only one. Yellowing of the leaves can also indicate that the soil is lacking other nutrients such as iron, manganese, or zinc.
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.
Overwatering
Watering issues are generally the most common cause of yellowing leaves.
Below are six signs you can easily recognize to determine if you are giving your plants too much fertilizer: Yellowing and wilting of lower plant leaves. Browning of leaf margins and tips. Black brown or rotting roots.
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.
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.
Epsom Salt for Plants
Aside from the anecdotal evidence about human benefits, Epsom salt does seem to help plants. Generations of gardeners have said it helps their plants grow bushier, produce more flowers and have better color. It's also said to help seeds germinate and repel slugs and other garden pests.
Animal-derived fertilizers tend to offer large amounts of nitrogen, and are therefore good for encouraging leafy growth. Bone meal is also a good source of phosphorus, and fish emulsion is a great all-purpose fertilizer.
When a leaf is yellowing, let the leaf fully turn yellow before pulling it off. When a leaf is on its way out, the leaf loses all of its chlorophyll (the molecules which make the leaf green), and the plant absorbs any leftover nutrients from the yellowing leaf.
If your plant's leaves are turning yellow, it might have a sulfate deficiency. If your plant's leaves are turning yellow but the veins remain green, it might have a magnesium deficiency. Epsom salts are a great solution for both of these problems.
Make up a solution of about a teaspoon of Epsom salts per litre (quarter gallon) of water in a spray bottle. Simply wet the foliage on your tomato plants every two weeks using a fine spray setting. It will quickly be absorbed by the leaves. Avoid spraying on hot, sunny days or when rain is imminent.
Nitrogen deficiency shows up as a general yellowing. Older, inner leaves turn yellow first. As it progresses, yellowing moves outward, eventually reaching young leaves, too. Potassium deficiency shows itself when leaf edges turn bright yellow, but the inner leaf stays green.
Chlorophyll is the “green” that trees synthesize from sunlight's energy and the water and nutrients taken up by a tree's root system. It's what makes tree leaves green. Green leaves turn yellow (become chlorotic) when a tree takes up too few mineral nutrients and doesn't synthesize enough chlorophyll.
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.
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.
If your plant leaves' color is alright, but they are becoming out of shape or deformed, stop using miracle gro on them. The deformation of leaves occurs when you are using too much miracle-gro on them. Weakened plants from either the stems or the roots are a sign of overdosing fertilizers.
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.
Leaf chlorosis is the result of mineral deficiencies, such as nitrogen, iron, or magnesium. Leaves turn yellow in response to nutrient shortages from poor soil (the problem can be made worse by overwatering, which leaches nutrients out of the soil).