It's impossible to recommend the "best" fertilizer without knowing the reason for the yellowing leaves. There are several potential causes, and the best treatment will depend on the underlying issue.
Here's a breakdown of common causes and appropriate fertilizer solutions:
1. Nutrient Deficiencies:
* Nitrogen (N): Yellowing starts at the older leaves and progresses upward.
* Magnesium (Mg): Yellowing appears between the veins of the leaves, leaving the veins green.
* Iron (Fe): Yellowing starts at the newer leaves and can be accompanied by a pale, whitish green color.
Solution:
* Specific Nutrient Fertilizer: Choose a fertilizer with a higher concentration of the deficient nutrient.
* Chelated Iron: For iron deficiency, use a chelated iron product.
* Soil Test: Get a soil test to accurately determine nutrient levels.
2. pH Issues:
* Acid-loving Evergreens: Evergreens like rhododendrons, azaleas, and blueberries prefer acidic soil (pH 4.5-5.5).
* Alkaline Soil: Alkaline soil (pH above 7) can make it difficult for evergreens to absorb nutrients, causing yellowing.
Solution:
* Acidifying Fertilizer: Use a fertilizer specifically designed for acid-loving plants.
* Soil Amendment: Add sulfur, iron sulfate, or aluminum sulfate to lower the soil pH.
3. Overwatering or Drought:
* Overwatering: Roots become waterlogged, leading to yellowing and leaf drop.
* Drought: Lack of water can stress the plant and cause yellowing.
Solution:
* Proper Watering: Water deeply and infrequently, allowing the soil to dry slightly between waterings.
* Mulch: Apply a layer of organic mulch to retain moisture.
4. Root Problems:
* Root Rot: Caused by overwatering or poor drainage.
* Root Damage: From construction, compacted soil, or pests.
Solution:
* Improve Drainage: Ensure adequate drainage to prevent waterlogging.
* Root Stimulant: Use a root stimulant fertilizer to help the plant recover.
5. Other Factors:
* Winter Injury: Cold temperatures and winter sun can damage evergreens.
* Disease or Pests: Infections and pests can cause yellowing and other symptoms.
Solution:
* Identify the Cause: Consult a local arborist or plant expert for diagnosis and treatment recommendations.
General Advice:
* Slow-release Fertilizer: A slow-release fertilizer will provide a steady supply of nutrients for a longer period.
* Organic Fertilizer: Organic fertilizers, like compost or manure, can improve soil health and fertility.
* Timing: Fertilize in early spring or fall, when the plant is actively growing.
* Observe: Monitor the plant's response to treatment. If the yellowing persists, seek professional help.
Remember: The best solution for yellowing evergreen leaves depends on the specific cause.
