When Bedding Plants Fail but Shrubs Thrive: Diagnosing a Decomposed Organic Layer and Root Disease

15 years of periwinkle succeeded, then one year failed—roots rotted. Since then, only liriope thrives. Back bed: tomatoes failed, Indian hawthorn ok.

Two Likely Problems

1. Periwinkle-specific fungal root disease. Hard to control. Use soil fungicide; don't replant periwinkle there for 3 years.
2. Decomposed organic layer. Years of mulch/leaves create a black, rich-looking surface that holds neither water nor nutrients. Roots stay in this layer and never penetrate real soil.

Fix

• Dig deep enough to reach mineral soil. Loosen it, mix some surface organic matter in, ensure plant roots are in soil, not just the loose layer.
• Use timed-release or organic fertilizer at planting. Spray-feed every 2 weeks with water-soluble fertilizer.

If Problems Persist

Take a plant (roots + soil) to a garden center for disease vs. culture diagnosis.