Fertilization is Important

You may need to apply fertilizer when you prepare the beds. Follow the recommendations of the soil test report. If you didn't test the soil, apply a complete fertilizer, such as 5-10-5, at a rate of 2 pounds (4 rounded cups) per 100 square feet. Work the fertilizer into the soil as you prepare the bed.

The ideal soil pH for most perennials is slightly acidic (6.0 to 6.8). If the pH is too low or too high (as determined by a soil test), adjust it at the same time you apply fertilizer. To raise the pH (make it more alkaline), add ground limestone as recommended by the soil test report, or at the rates indicated in Chart 1.

To lower the pH (make it more acidic), add sulfur, ferrous sulfate (iron sulfate)

or aluminum sulfate as recommended by the soil test report, or according to the rates in Chart 2. Rates for aluminum sulfate and iron sulfate need to be five times those given for sulfur.

Adding generous amounts of organic matter will also help to lower soil pH and keep it at the desired level. Normally, pH needs to be adjusted only once, but it is desirable to test the soil the following year to be sure the pH is at the recommended level. If not, topdress the soil with limestone or aluminum sulfate.

To increase soil moisture retention, spread a 2- to 3-inch layer of mulch over the surface of newly prepared beds. Use bark chips, leaf mold, pine needles, well rotted sawdust or compost. This will also help suppress weeds and increase plant hardiness. Apply only a thin layer of mulch to heavier clay soils because these soils do not drain as rapidly and may stay wet too long. You may need to add organic mulch each year as it decomposes. Plastic mulch is not recommended. Rock mulch is best used only in rock gardens.


Pounds of ground limestone needed per 100 square feet to raise pH to 6.5.

Soil pH

Sandy loam Loam

Clay loam


8 10



6 8



3 4


CHART 2. Pounds of sulfur needed per 100 to lower pH to 6.0.

square feet

Soil pH

Sandy loam Loam

Clay loam


1.8 2.5



1.4 2.0



0.8 1.2


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