In the Houston area soil is poor for most of us. We either have sand or clay. Rare is the lucky soul with loam. To make matters worse we tend toward alkaline soil, the more north and west you go the worse it gets. Then the heat and humidity rapidly breaks down what little organic matter the soil contains. This means we see lots of nutrient problems with plants. Plants need much more fertilizer here than anywhere else you’ve lived, but the biggest pollutant in our bayous is fertilizer run off. So feed your plants lightly and frequently and watch for signs they may be missing something.
If you are seeing yellowing leaves with green veins you might want to check your plants secondary nutrients. Iron is usually but not always the cause of green veined, yellow leaves. Sulfur deficiency effects new leaves first, calcium and magnesium effect older leaves first all have the same tell tale green veins and yellow leaves.
Calcium deficiency – Youngest leaves looked bleached, especially at the tips of the leaves. Leaf tips rolls and appear scorched. Along the edges of the leaves the veins remain green while leaf looks bleached out. New leaves may be distorted in shape. Old leaves turn brown and die. Growth is stunted, new buds don’t grow. In vegetables you get blossom end rot and black spots in things like celery, carrots and cabbage. Usually this only occurs in very acidic soil.
Calcium is needed to build plant cell walls, and to help move nutrients through out the plant.
Calcium is usually not a problem if your soil pH is between 6-8. Too much or too little water can also effect calcium levels in the plant. If calcium is low, soil is not properly buffered ( pH can swing rapidly making nutrient uptake difficult ). Around here blossom end rot on tomatoes is a common symptom.
Magnesium deficiency – Older leaves become yellow, while veins remain green. Leaves drop off plant. Leaves may curl up at edges and edges become red-brown-purple in color leaving a green arrowhead shape in the center of the leaf.
Magnesium is needed for photosynthesis it is the main element in the chlorophyll molecule. It helps the plant uptake iron and also to move nutrients around the plant.
Add epsom salts 1 teaspoon per gallon twice a year to fix a magnesium deficiency.
Sulfur deficiency – Youngest leaves yellow, veins remain green. Plant is slow growing. Leaves curl. Often sulfur is not deficient but rather just low compared to the amount of nitrogen in the soil. Sulfur deficiencies are rare. Adding sulfur will help lower your soil pH, slowly and lightly, so don’t be afraid to add some to your soil if your pH is higher than 7.0.
Too much of these nutrients are not usually a problem except that other nutrients can’t keep up. So too much of any of these may cause a deficiency in another nutrient.