Question: How can I tell when my plants need to be fertilized?
Answer: They’re going to give you the telltale symptoms. Nitrogen shortages will be the most common. The plants’ growth will slow and their leaves won’t be the deep, rich green you would normally expect. The yellowish-green color will be over all of the plant, not just on the new growth. Phosphorus deficiency is much less common. When it does show up, however, it will be seen as stunted growth with a purplish cast to the leaves. You’ll see it on newly seeded bermuda lawns that have been kept too wet, but you’ll rarely encounter it elsewhere. Iron deficiency will have symptoms of yellowed leaves with dark green veins, most prominently displayed on the newest growth first. Lots of other problems resemble iron deficiency, but they won’t match all of those symptoms. Zinc deficiency (pecan rosette) is common only to pecans, and only west of Interstate 35. It causes a stunted dieback of the pecan branches, also referred to as “witches’ brooms.” As for timing of feedings, all of these elements will be most quickly assimilated by the plants if they’re applied several weeks prior to vigorous growth. Most feedings will be made in early spring, late spring and early fall, but timing will vary with the crop. Zinc should be applied as a foliar spray, and you should include it with each application of insecticide that you make from May through the summer.