How to Properly Diagnose Plant Deficiencies

June 01, 2011 | 2:06 pm

After enjoying an afternoon of swimming, we came home for more water fun – that is watering the garden and flowers. Watering is a chore that cannot be skipped during hot summer days. As I was watering my day lilies I noticed yellow leaves. I turned my attention from watering to diagnosing. Something was causing this change in color. Just like the change in my skin, it went pale to sun burnt while swimming. This was the results of letting a nine-year old apply my sun screen; not my brightest moment as a parent. Plants can change color when they are missing nutrients, have too much or too little water, or are stress by the environment.

Since I have not taken a soil sample from this bed, I don’t know exactly what is missing in this particular soil. The yellow on the leaf from the tip down, is a telling characteristic of nitrogen deficiency. Magnesium, iron, and sulfur deficiencies also result in yellowing leaves so I need to be careful to properly diagnosis.

Signs of Nitrogen (N) Deficiency

  • Yellowing of older leaves at the bottom of plant.
  • Plant is generally light green.

Signs of Magnesium (Mg) Deficiency

  • Yellowing of older leaves from the edge leaving a green arrowhead shape in the center of the leaf.

Signs of Sulfur (S) Deficiency

  • Yellowing of the younger leaves first and then the older leaves.

Signs of Iron (Fe) Deficiency

  • Yellowing begins on the newer leaves.
  • The internal veins are often still green.

After examining the plants, I’m fairly confident that the day lilies are not getting the nitrogen they need. I need to correct this issue as nitrogen deficient plants can’t make their own cells and are stunted in growth. That simply will not due; I enjoy the day lily blooms too much.

These day lilies have been fertilized. I know that there is nitrogen in the soil but that nitrogen is obviously not available to the plant. My suspicion is soil pH. Soil pH controls how available nutrients are to plants. Soil with a low pH is highly acid. To raise the levels we amend the soil with lime. There are soil pH kits and meters available at garden centers. I have looked at them many times, but have never purchased them. Now I have a reason and will test the soil before amending with lime. As I aspire to follow the 4 R’s of nutrient management: right source, right rate, right time and right place, I must gather as much information as I can before amending the soil.

After applying some aloe vera to my own discolored skin, I’m headed back to the garden center to get the right tools for testing soil pH.