Question of the Week
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Our question this week is on leaves that are turning yellow and what fertilizer to use on them. First of all, take a closer look at the plant.
Which leaves are yellow? Is it the older, lower leaves, or the new, upper leaves?
Is it overall yellowing or yellowing with prominent green veins?
There are two common nutrient deficiencies in our area: lack of nitrogen and lack of iron.
A nitrogen deficiency will show some symptoms of overall yellowing on the older leaves and that's because nitrogen is what we call a mobile nutrient. The plant will take nitrogen from its older leaves and send that element to its younger leaves to protect itself and keep growing in times of stress.
But iron deficiency shows up as yellow leaves with green veins on your newer leaves, not on the older leaves. And that's because iron is an immobile nutrient. The plant can't take it from its older leaves and move it to its younger, newer tissue.
Most fertilizers do contain nitrogen, but they don't all contain iron. There are three numbers on the front of fertilizers and they are (N) nitrogen- (P) phosphorus-(K) potassium. The fertilizer may contain micronutrients like iron, so check the label. You may need to supplement with a product that adds iron.
If your plants are deficient, give them a quick fertilizer boost with a liquid fertilizer. Then go back and apply a slow release fertilizer if you like. Ideally, just add compost for plant and soil health.
But don't assume your plant needs fertilizer, look closely at it. It may not be related to fertilizer at all. It could be many other problems: