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6 Mistakes That Cause Iris Leaves to Turn Yellow (And How To Fix It)

Irises are tough, long-lasting flowers and among the simplest to care for. Yet, they do need certain conditions to stay healthy. Sometimes, problems may arise, evident through their leaves.

If your iris leaves are turning yellow, it might be a sign you’re watering them too much. A soil check can confirm this – if it feels overly wet, it’s time to ease up on the watering.

Next, I’ll walk you through all the potential reasons behind yellowing iris leaves and offer advice on what to do for each scenario.

1. Overwatering

iris leaves turning yellow

Iris leaves turned yellow due to overwatering.

Overwatering irises can lead to a problem called leaf spot. This issue appears as circular patches on the leaves that first turn yellow, then light brown, and finally dry out. These spots vary in shape and size, mainly due to the soil being excessively moist for extended periods.

Here’s what you can do:

  1. Cut away the parts of the leaves affected by leaf spot.
  2. Water your irises only when the top 3 inches (about 7.5 cm) of soil are dry.
  3. Ensure good drainage.

2. Not Enough Sunlight

Generally speaking, irises require at least 6 hours of direct sunlight daily. They come in various sizes, including short, medium, and tall. Tall bearded irises thrive best with uninterrupted sunlight throughout the day and shouldn’t be placed in shaded areas. On the other hand, short bearded irises and other irises of medium and short stature do well with just 6 hours of sunlight.

Here’s what you can do:

  1. Move tall irises to a spot where they can enjoy 12 hours of sunlight daily.
  2. Relocate intermediate and short irises to areas where they’ll receive 6 hours of sunlight daily.
  3. Trim any branches from trees that may be shading your irises too much.

3. Inappropriate soil pH

The soil pH where plants grow is crucial, and for irises, it should ideally be around 6.8. If the soil is too acidic (low pH) or too alkaline (high pH), the nutrient availability in the soil changes because of chemical reactions. This can lead to a nutrient deficiency, which often shows up as yellowing in the leaves.

Here’s what you can do:

  1. Test the soil pH first.
  2. If you need to decrease the pH, add sulfur to the soil.
  3. To increase the pH, mix in some limestone powder.
  4. Consider replanting your irises in soil with the correct pH that also offers better drainage.

4. Pest Damage

iris leaves turning yellow

Iris leaves damaged by slugs.

Different insects can attack irises, leading to stem and leaf damage that results in yellowing. While irises are generally resilient to pests, they’re not immune.

Aphids and scale insects feed on the stems and leaves, draining the plants of nutrients and causing yellow spots or overall yellowing. Aphids are tiny green bugs found moving around the stems and more hidden parts of the leaves. Scale insects, on the other hand, look like bumps on the stems and leave behind a black, dry, crispy waste.

Here’s what you can do:

  1. Regularly inspect your irises for any signs of pests.
  2. Treat them with horticultural oil to combat the infestation.
  3. Apply the oil again after some time to ensure all pests are eliminated.

5. Underwatering

iris leaves turning yellow

Iris leaves turned yellow due to underwatering.

When the soil becomes overly dry, the roots of plants, including irises, struggle to absorb and distribute nutrients to the stems, leaves, and flowers. This lack of hydration can lead to the leaves turning yellow. Additionally, the leaf edges may dry out, turning brown and brittle.

Here’s what you can do:

  1. Water your irises as soon as the top 2-3 inches of soil feel dry.
  2. Keep an eye on the soil’s moisture level weekly, continuing until the yellowing of the leaves stops.
iris leaves turning yellow

Iris leaves turned yellow due to pest infestation.

6. Overfertilization

While several issues can lead to yellowing iris leaves, soft rot is a distinctive problem. You’ll notice the rhizome feeling soft and mushy, similar to spoiled produce. To check for soft rot, gently probe around the rhizome with your finger; it should feel firm, akin to a fresh sweet potato.

Irises aren’t demanding in terms of soil nutrients, and the average potting mix or garden compost is often too rich for them. Additionally, soft rot can arise if the soil stays damp for too long, typically due to overwatering.

Here’s what you can do:

  1. Use a soil mix that’s half compost and half regular garden soil when replanting irises.
  2. Choose a planting spot where water drains well, avoiding areas where water tends to accumulate and soil becomes soggy.
  3. Fertilize your irises once annually in the spring with a slow-release, all-purpose fertilizer.

Julia Johnson

Tuesday 23rd of May 2023

Good article. Thank you!