What are the signs of nutrient deficiency in my lawn? (ASK Advice)

It's the time of year when many lawns are showing signs of stress, whether due to excessive heat, excessive water, diseases, and pests. In a previous ASK Advice article, we covered some tips to differentiate these various causes of brown patches in your lawn. But what about other troubling symptoms, like pale yellow leaves, dark purple leaves, or stripes? These could be indicators of nutrient deficiencies.

Yellow leaves. In scientific terms, pale green or yellow coloration of leaves is called chlorosis, which can be caused when essential plant nutrients are missing, notably Nitrogen but also Sulfur.

Healthy (left) vs. sulfur-deficient (right). Image source: CIMMYT

Purple leaves. A Phosphorus deficiency tends to turn grass blades dark green and eventually purple. This color change can also be caused by cold stress, but that's unlikely this time of year!

Corn with Phosphorus deficiency (corn is member of the grass family too!). Image attribution: Wikimedia Commons.

Brown edges. The tell-tale sign of a Potassium deficiency is grass blades looking scorched along the edges while the center stays green.

Corn with a Potassium deficiency. Image attribution: Alandmanson via Wikimedia Commons.

Striped leaves. This happens when the veins on the leaves stay green while chlorosis takes over inbetween. This is most commonly caused by deficiencies an Iron deficiency, but could also be a Magnesium or Manganese deficiency.

Corn leaf with a Magnesium deficiency. Image attribution: Alandmanson via Wikimedia Commons.

If you're still unsure whether you're dealing with a nutrient deficiency or another issue, you can consider whether the discoloration is uniform across your lawn or patchy and variable. Typically, nutrient deficiencies will be persistent across your yard since the soil properties and ammendment history will be similar. By contrast, diseases and other issues tend to be more localized or spread erratically. Another consideration is how quickly you saw the symproms develop. Nutrient deficiencies tend to worsen gradually over time, while infections can pop up overnight.

Can your grass have nutrient deficiencies even though your soil test report showed sufficient levels? Surprisingly, yes -- nutrients in the soil might not be absorbed into roots if the pH is too high or too low, or if there's not enough water flowing throug hthe soil to actually deliver the nutrients where they're needed. So, as always, the best way to stay on top of your lawn's health is to get your yearly soil testing done to monitor both nutrient levels and pH. If needed, you'll be able to fertilize with any missing nutrients before they cause these problems!