What Is an Acidifying Agent for Roses?

pH Guideline

• Roses grow best in slightly acidic soil, with a pH of approximately 6.5. At this level, soil facilitates the absorption and uptake of nutrients and makes them available to roses. If pH is too low, roses experience metal toxicity, which hinders flowering and root and shoot growth, according to Washington State University Extension. If pH is too high, roses display yellowed leaves and stunted growth. Adjusting soil pH before planting gets newly planted roses off to a healthy start.

Soil

• The American Rose Society recommends sulfur as an excellent acidifying agent for soil around roses. Clemson University Extension advises not to confuse sulfur as a soil acidifying agent with sulfur as a plant nutrient. Standard soil test reports recommend adding 10 pounds of sulfur per acre as a plant nutrient. Sulfate sulfurs are found in mixed fertilizers and they will not acidify soils. Elemental sulfur acidifies soil after soil bacteria oxidizes it. Soil testing determines soil pH and indicates how much elemental sulfur is needed to acidify soil.

Water

• The pH of the water you use to irrigate roses is extremely important and is one of the determining factors in how well your roses grow, according to the American Rose Society. Municipal water supplies contain chlorine and fluoride, which contain salts and chemicals that can injure plant tissues. Rainwater contains more oxygen than tap water and is healthier for roses. Rainwater is a slightly acidic agent for watering roses and can benefit plants if acidic concentrations are not excessive. Litmus paper indicator test strips can be used to determine the pH of irrigation water.

Cut Flowers

• Gardeners want to enjoy fresh-cut roses as long as possible. Extending the vase life of flowers is possible by using an acidifying agent, such as packaged floral preservatives or citric acid. Penn State College of Agricultural Sciences says that 1 tablespoon of powdered citric acid will acidify 4 gallons of water and will greatly improve vase life. An acidifier works by matching the pH of water more closely to the pH of plant cell sap, which reduces the stress on flowers that are removed from their parent plants.