Viburnum plants are popular additions to many gardens, admired for their diverse forms, attractive foliage, and often fragrant flowers and berries. While generally low-maintenance, proper nutrition through strategic fertilization supports their health, vibrant growth, and abundant blooms. This guide outlines how to effectively fertilize viburnums.
Does Your Viburnum Need Fertilizer?
Observe your viburnum to determine if it needs fertilizer. Healthy viburnums, especially those in good soil, often don’t need regular feeding. However, stunted growth, yellowing leaves, or reduced flowering indicate a nutrient deficiency and may benefit from additional nutrients.
A professional soil test is the most accurate way to assess nutritional needs. It reveals existing nutrient levels (nitrogen, phosphorus, potassium) and soil pH. Viburnums generally prefer a slightly acidic to neutral soil pH, typically ranging between 5.5 and 8.0, depending on the specific variety. A soil test provides precise information to tailor fertilization, preventing unnecessary application.
Choosing the Right Fertilizer
Choose fertilizer by understanding the NPK ratio (Nitrogen, Phosphorus, Potassium percentages). Nitrogen promotes lush foliage growth, while phosphorus supports healthy root development, stem strength, and the production of flowers and fruit. Potassium contributes to the plant’s overall health, resilience, and its ability to absorb other essential nutrients.
Many viburnums benefit from a balanced, slow-release fertilizer, such as a 10-10-10 or 15-15-15 formula. For varieties prized for their blooms or berries, a fertilizer with a slightly higher phosphorus content, like a 5-10-5, can encourage more prolific flowering. Applying too much nitrogen, however, can lead to excessive leafy growth at the expense of flowers. Both synthetic and organic fertilizer options are available. Synthetic fertilizers offer precise nutrient ratios and are often fast-acting, whereas organic options like compost, well-rotted manure, or bone meal improve soil health over time by releasing nutrients slowly.
When and How to Fertilize
Fertilize viburnums in early spring, before new growth, to boost nutrients as the plant emerges from dormancy. An application after flowering can also be beneficial for some varieties or to enhance blooming and foliage. Avoid fertilizing in late summer or fall, as this stimulates tender new growth vulnerable to winter frost damage.
For granular fertilizer, spread it evenly around the plant’s drip line (the area beneath the outermost branches). Begin spreading about one foot away from the main trunk to prevent root burn. After application, water thoroughly to help nutrients penetrate the soil and reach roots. If using liquid fertilizer, dilute according to manufacturer’s instructions and apply to the soil around the plant’s base. Always adhere to dosage recommendations on the fertilizer label.
Post-Fertilization Care and Common Issues
After fertilizing, ensure adequate watering. This dissolves nutrients, carries them to the root zone, and prevents fertilizer burn that can scorch leaves. Watering the soil both before and after applying fertilizer can aid in even distribution and absorption.
Over-fertilization can cause leaf scorching or excessive leafy growth with fewer blooms. To prevent this, follow recommended application rates and avoid over-applying nitrogen. Incorporating organic mulch, such as pine bark, around the viburnum’s base provides ongoing benefits. A 2-4 inch layer helps retain soil moisture, suppresses weed growth, and moderates soil temperature, supporting the plant’s overall health. Keep mulch a few inches from the trunk for proper air circulation.