Get your soil tested and prepared for spring planting

  • Have your soil tested if you want to be sure which fertilizer is best for your garden.

    Have your soil tested if you want to be sure which fertilizer is best for your garden. Courtesy of Chicago Botanic Garden

By Tim Johnson
Chicago Botanic Garden
Posted5/1/2022 7:00 AM

Apply fertilizer to garden beds if needed. Most gardens in the Chicago area have soil with adequate levels of phosphorus, so choose a fertilizer with little or no phosphorus.

The higher the percentage of nitrogen in the fertilizer you purchase, the less you need to apply to your garden, so follow instructions on the bag or ask a salesperson for advice. Applying too much fertilizer will have adverse effects on the health of plants.


Have your soil tested if you want to be sure which fertilizer is best for your garden. Use soil from a few locations for a good composite sample. If your garden is large, break up your property into sections and test multiple samples.

If your soil is too alkaline, elemental or granulated sulfur may be added to lower the pH. Rhododendrons and azaleas are examples of plants that can benefit from sulfur applications in many gardens in the Chicago area.

If you want to get blue hydrangea flowers back to blue, apply sulfur to hydrangeas that are turning pink. The flowers turn pink in more alkaline soils. Add 4 pounds of sulfur per 100 square feet of garden area per year. It is best to apply in the spring and fall, applying one-half of the recommended rate each time.

Sulfur that is applied at too high of a rate can burn plants. Work the sulfur into the soil and water in. Sulfur is slow acting. Wear protective gloves and be careful to keep the dust out of your eyes when applying.

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• Many gardens are still too wet to work in, so be sure to give the soil time to dry out before starting to work.

• Many garden beds have irregular edges. Beds look better and are easier to mow along if they have smooth, flowing curves.

Use a pliable garden hose or rope to lay out your new bed line. All clumps of grass should be removed from the bed and any clods of soil should be broken up and spread around.

• Avoid the "volcano effect" around trees that is caused by piling soil and mulch up around the trunk. Use a flat spade to carefully remove any soil that has built up over time around the base of your trees. In most situations, it is best to move the excess soil to a low area or compost pile.

• Tim Johnson is director of horticulture at Chicago Botanic Garden,

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