MSU Extension Soil Web pages for Consumers

Perennial Flowers, Bulbs and Roses

Some perennials respond well to high fertility,  such as astilbe, chrysanthemum, delphiniums, lupine, peonies and summer phlox .  Others will grow taller and leafier, but not stand up or flower as well if they have plenty of nitrogen.  Organic matter added at the time of planting can provide sufficient nutrients for many years, or an inch of compost added to the surface each year. Depending on the fertility of your soil, light and water conditions, you may wish to use little or no fertilizer on perennials.  Research your plants, or experiment, perhaps starting with half the recommended rate of nitrogen and the full amount of phosphate and potassium needs determined from your soil test.

Here is a sample recommendation:( see below for bulbs and roses)

Use a fertilizer calculator, enter your recommendation and the fertilizer you want to use, and the calculator will tell you how much to buy and apply,

or Learn to calculate  the amount of fertilizer that will meet the recommendations.

Timing and number of applications: Use slow-release fertilizers and/or apply at intervals during the growing season.  Work in up to half the recommended nitrogen and all the other materials before planting a new area, saving the balance of nitrogen to apply in portions each month or two during the summer, to get new plants off to a good start.

Hardy bulbs need similar fertilization to other perennials, but surface applications of phosphorus and potassium will not reach the deep root systems of the larger bulbs. That is the reason for traditional practices of putting "bulb booster" and/or bone meal into the planting hole or working such fertilizers deeply into the bed before planting. Nitrogen, on the other hand, will move down into the soil with rain or irrigation and very little, if any, should be put into the planting hole.  Spring, just before flowering, is a good time to surface apply the balance of nitrogen to the bulbs.

Tender bulbs may be fertilized as  annual flowers.

Roses grow best in soil that is in the pH range of 5.5 to 6.5, so adjusting the soil pH may be important for success. Work the recommended fertilizer into the soil before planting new roses.  Fertilizer applications to planted roses should not begin until new spring growth is well established and all danger of severe freezing is past.  Use slow release fertilizer or apply portions of the recommended nitrogen every month or so until August 1, when nitrogen applications should stop for the year.  Late applied nitrogen may stimulate fresh growth and delay hardening of the wood before winter.