Apply fertilizer to the flower beds if necessary. 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 buy, the less you need to apply to your garden, so follow the instructions on the bag or ask a salesperson for advice. Applying too much fertilizer will have adverse effects on plant health.
Have your soil tested if you want to be sure which fertilizer is best for your garden. Use soil from a few places for a good composite sample. If your garden is large, divide your property into sections and test several samples.
If your soil is too alkaline, elemental or granular sulfur can be added to lower the pH. Rhododendrons and azaleas are examples of plants that can benefit from sulfur applications in many Chicago-area gardens.
If you want to turn blue hydrangea flowers back to blue, apply sulfur to hydrangeas that turn pink. 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 half the recommended rate each time.
Sulfur applied at too high a rate can burn plants. Work the sulfur into the soil and water it. Sulfur acts slowly. Wear protective gloves and be sure to keep dust out of your eyes when applying.
• Many gardens are still too wet to work, so be sure to allow time for the soil to dry out before you start working.
• Many garden beds have jagged edges. Beds look better and are easier to mow if they have smooth, flowing curves.
Use a flexible garden hose or rope to lay out your new bed line. All clumps of grass should be removed from the bed and all clods should be broken up and spread around.
• Avoid the “volcano effect” around trees caused by piling up soil and mulching around the trunk. Use a flat spade to carefully remove soil that has accumulated over time around the base of your trees. In most situations, it’s best to move excess soil to a low area or compost pile.
• Tim Johnson is director of horticulture at the Chicago Botanic Garden, chicagobotanic.org.