All shrub roses benefit from some form of fertilizer to amend the soil and boost plant productivity. Fertilizers designed for roses come in both organic and synthetic formulations. Which formulation you use comes down to personal preference but many rosarians swear by the use of one or more organic formulations for optimal shrub rose performance with minimized concerns over tainted runoff. The frequency of feeding will depend on the form of fertilizer used and can vary from monthly to just once or twice per year applications.
Clean up the soil around the base of the shrub rose before every time you apply fertilizer to encourage good penetration into the soil and prevent disease-prone conditions. Lift up and discard any dropped petals or leaves laying on the soil surface. Pull up errant weeds and remove or thin encroaching plants so that the area from the main trunk out past the drip line of the shrub is free of debris.
Apply organic fertilizers to the soil around your shrub roses beginning in the early spring after the last frost has passed. Organic fertilizers for roses come in many forms including liquid, powder, crystal and granule. Choose one or more in combination to provide nitrogen, potassium and phosphorous. Always apply in the recommended dose and scratch the product lightly into the top inch or two of soil with a cultivating fork to aid in penetration. Rose tone, fish emulsion, organic rose food, well-aged manure and/or compost are all good options to feed your shrub roses. As a rule of thumb, organic fertilizers should be applied at least three to four times per growing season but more can be required for optimal performance depending on soil conditions, climate and the shrub species.
Feed your shrub roses with a commercial synthetic (chemical) rose formula in the spring just as you begin to see new growth and the last frost has passed. Make a second application when the rose buds appear and begin to swell and a third in midsummer to support ongoing blooming. In warmer climates where frost is rare or minimal and the shrub roses continue to bloom well into fall, a fourth application in early fall can be added to the regimen. Follow the dosing directions on the label from your product of choice and always err on the side of weaker applications applying between 50 percent to 95 percent of the recommended dose.
Foliar feed your shrub roses once in the late spring and again in the early fall according to package recommendations. Rose leaves and stems respond well to spray feeding with organic diluted kelp extract, but synthetic foliar product options can readily be found in garden centers and nurseries.
Water in any fertilizer well after application allowing the water to percolate down into the soil before watering a second time. Mulch over the base of your roses with a organic material such as shredded bark, compost or cocoa bean hulls to hold moisture to the soil, enrich the soil and prevent the fertilizer from being displaced.