This Is The Best Time To Fertilize Roses

There’s no flower more classic in the garden than a rose. Whether you grow hybrid tea roses, old climbing roses, or floribundas, the nutrients they receive make the difference in a healthy, profusely blooming plant or stunted growth. Learn more about nutrient requirements and the best time to fertilize roses.

Understanding Rose Nutrient Requirements

It takes a lot of energy for roses to produce flowers year after year and roses are heavy feeders from the soil. Most balanced fertilizers, especially those formulated for roses, contain macronutrients (nitrogen, phosphorus, and potassium) and micronutrients (iron, calcium, and magnesium).

Macronutrients

• Nitrogen (N): Essential for robust foliage growth and overall plant health. Nitrogen deficiency appears as stunted plant growth and pale green or yellow leaves.
• Phosphorus (P): Promotes healthy root development and growth. Phosphorus deficiency produces a weak root system, causing stunted growth, less blossom production, distorted leaves, and early plant death.
• Potassium (K): Essential for bud and flower formation and disease resistance. A lack of potassium causes poorly developed buds, reduced flowers, and a weakened plant structure.

Micronutrients

As the name implies, roses require small amounts of micronutrients. A soil test can confirm whether supplementary feedings are needed or you can look for these signs of a deficiency.

• Calcium (Ca): Reduced petal formation and weaker cell walls in the stem and leaves.
• Magnesium (Mg): Yellowing between leaf veins and weakened stems.
• Sulfur (S): Yellowing of leaves.
• Boron (B): Malformed new leaves.
• Copper (Cu): Cupped leaves.
• Iron (Fe): Pale or yellowing leaves and reduced vitality overall.
• Manganese (Mn): Pale leaves with deep green veins.
• Zinc (Zn): Malformed leaf growth.

Soil pH

The relative acidity or alkalinity of the soil affects how well roses can access nutrients in the soil. Roses prefer a slightly acidic to neutral pH (6.0-6.9) so it’s important to have soil tested before you begin amending it with fertilizers. Ammonium-based fertilizers can make soil more acidic, while nitrate-based fertilizers are less acidic. 

Soil tests can be purchased at gardening centers or by contacting your local cooperative extension service office.

Timing for Fertilizing Roses

Healthy repeat-blooming roses require nearly year-round feeding from early spring to fall to remain vigorous and resist diseases. Some varieties, such as tea roses, require more nutrients than less demanding varieties like shrub roses.

Early to Mid-Spring

For all types of established roses, apply fertilizer after there is no danger of a late frost or when about six inches of growth has appeared. A granulated, balanced fertilizer like 10-10-10 NPK or one specially formulated for roses can be scattered evenly at the drip line or outermost branches of the rose bush. Use about 1/4 cup of 10-10-10 per average-sized bush and follow label directions for rose-specific formulas. Always water the plant well after each fertilizer application.

For newly spring-planted roses, wait at least six weeks before applying fertilizer to allow the plant to become established and begin to show new growth. Use half the recommended amount of diluted liquid fertilizer to prevent over-fertilization that can burn tender roots.

Throughout the Growing Season

During the growing season, fertilize roses using 1/4 cup of a 10-10-10 NPK or a special rose formula (follow label directions for usage amount) after each bloom cycle. As the season progresses, gradually reduce the amount used as the end of August nears.

Late Summer to Early Fall

You should stop fertilizing roses or switch to low-nitrogen formulas six to eight weeks before the first average frost date is predicted to prevent new tender growth susceptible to cold and pest damage. To help roses into winter dormancy, add a thick layer of mulch to protect roots and conserve moisture.

Types of Fertilizers for Roses

Organic Fertilizers: Commercially-sold organic fertilizer is derived from natural sources such as manure, fish emulsion, bone meal, or compost and is available in granular and liquid form. They typically break down more slowly than synthetic fertilizers reducing the risk of root burn. Organic fertilizers also add microbes to the soil that boost worm growth and improve the physical structure of the soil. While some rose growers make their own organic “tea” to use, if you are a novice use a packaged organic fertilizer and follow label directions for application.

Inorganic Fertilizers: Made from synthetic chemicals, inorganic fertilizers are sold in granular, time-release, and liquid formulas. Inorganic fertilizers are usually less expensive than organic fertilizers and provide all the macronutrients roses need to thrive.

Pre-packaged Rose Fertilizers: Whether made with organic or inorganic compounds, pre-packaged rose fertilizers are more likely to have a higher phosphorus level and the micronutrients roses need than a basic fertilizer.

Fertilizing Container Roses

The frequent watering required by container roses leaches nutrients from the soil more quickly than garden-planted roses. Throughout the growing season, apply a balanced, water-soluble fertilizer every four to six weeks following the dilution rate on the label. Look for signs of leaf-yellowing and fertilize more often until the plant rebounds. Stop adding fertilizer in the fall as the roses go dormant for winter.

Best Practices for Fertilizing Roses

• Apply fertilizer when the soil is moist, and thoroughly water the roses after each application.
• Do not apply fertilizers during periods of extreme heat or drought.
• Keep a rose fertilization calendar for each type of rose so you won’t forget a feeding or over-fertilize.
• Foliar sprays are best used to control rose pests and diseases rather than to add nutrients because they can’t replace healthy soil. However, high-nitrogen sprays will give a rose with yellowing leaves a quick boost until you can evaluate and amend the soil.
• Over-fertilization can be just as damaging as not fertilizing roses, resulting in burned roots, overgrown or damaged foliage, and fewer blooms. If you see a white crust forming on the soil in the garden or container, you’re fertilizing too often.