May in the garden: Botanic Garden explodes in color this month – yours could too

May is a busy month in the garden and a time of fast change as the weather warms up and plants come into flower. The Botanic Garden explodes with color in May.

Divide perennials early in the month as needed to fill in any holes, and make notes about areas that could use more bulbs for planting in fall.

General garden careTry to avoid growing plants that are invasive or potentially invasive because they can spread out of control to natural areas and threaten native plants and animals. This is a good time to remove these plants from your garden and replace them with similar-looking plants. For example, Freeman maple cultivars such as Autumn Blaze are good alternatives to Norway maple. The Botanic Garden website (chicagobotanic.org) has a list of plants considered invasive in Chicagoland along with suggested substitutes. It is a good idea to pace yourself as the gardening season starts so you can get used to the physical labor and avoid injuries. Gardening can involve a lot of lifting and bending. Try to keep loads close to your body as you are moving them. It is best to bend at the knees, keep your back straight and avoid twisting your back as you lift. Lift with your legs and keep your eyes focused ahead to help keep your back straight. Tightening your abdominal muscles will also help hold your back in a good lifting position. Back injuries can occur not just because of heavy loads but because of cumulative stress. Even a simple task like picking up a flat of annuals by bending at the waist can cause injury. If you have a lot of digging to do in your garden, it#146;s important to have your utilities located first. These free services can make sure you do not accidentally damage an underground gas, water or power line. In the suburbs, call JULIE at (811) or (800) 892-0123 or see illinois1call.com. In Chicago, call DIGGER at (312) 744-7000. It generally takes two working days for these services to locate your utility lines, so allow plenty of time before you need to dig. These locating services will not mark any lines you have installed yourself, such as a gas line to a grill or wires for landscape lighting. Dig carefully by hand if you are working within 18 inches to either side of any marked underground utilities. Also use care when digging in gardens with underground sprinkler systems.Gradually move houseplants outside to protected areas once night temperatures remain above 40 degrees. Keep them in shade at first to acclimate them to the increased sunlight and avoid burning the foliage. Large houseplants in plastic pots should be slipped inside larger, heavier pots to prevent them from blowing over. Prune and repot the houseplants as needed. Carefully monitor them for insects during their time out in the garden.Consider pruning spring-flowering shrubs and ornamental trees immediately after they bloom to maximize next year#146;s flowers while controlling the size and shape of the shrubs for this year. These plants set their flower buds in early summer, so cutting them back in early fall or winter will remove flower buds. Selective thinning or renewal pruning of branches will have much less impact on flower buds. These plants include forsythia, viburnum, lilac, small magnolias, rhododendrons and azaleas. AnnualsWhen purchasing summer annuals, look for even, bushy growth that fills out the pot, not necessarily plants that are in full flower. I prefer annuals that have good strong foliage over those that have been pushed to flower at a small size in cell packs. Fertilize annuals that were grown in cell packs after planting or they may lose vigor. If annuals are leggy, pinch them back to encourage lateral or bushy growth. After removing annuals from cell packs, check the roots. If they are circling in the small mass of planting medium, break them apart before planting. Be cautious about planting frost- and cold-sensitive plants such as tomatoes, peppers, eggplant, impatiens and coleus in early May. The average frost-free date at the Botanic Garden is May 15, but frosts can occur later away from Lake Michigan. To determine how many plants you need for a bed, first calculate the square feet of the bed by multiplying its length by its width. Calculate how many square feet each plant will take up and divide the square feet of the bed by this number. The number of plants will vary with their spacing, which will depend on how large they will grow to be and how fast you want them to grow together. For example, suppose the bed is 8 by 7 feet and you plan to install impatiens on 6-inch centers (meaning that the distance from the center of one plant to the center of the next is 6 inches). Multiply 8 by 7 to determine that the bed is 56 square feet. To determine how many square feet each plant needs, first divide the spacing (in inches) by 12 inches to find the fraction of a foot; in this example, 6 inches divided by 12 equals half-foot spacing. Since the spacing applies in two directions, multiply .5 by .5 to find that each plant will need .25 square foot. Divide the 56 square feet of the bed by the .25 square foot per plant to determine that 224 impatiens that are needed. If the flats have 48 plants, you would need five flats with a total of 240 impatiens.If the growing medium in your container or window box is only one year old, you can use it for another season. Simply remove any root balls from last year, fluff the medium with a trowel and top-dress with new medium as needed to fill in any low spots. Be sure to fertilize annuals when reusing growing medium. I like to use a slow-release fertilizer. If your potting soil is a couple of years old, it is a good idea to remove half of it and fill in with new medium, making sure to mix the old and new well. Growing medium that has been in use for more than two years should be completely replaced.Lawn careSpring rains and warm weather create a perfect environment for turf grass weeds such as dandelions. Use a hand tool to dig weeds out before they go to seed and create more problems in upcoming years. If hand-weeding is not feasible, use an herbicide for controlling broad-leaved weeds in turf grass. Herbicides are most effective when weeds are young and actively growing. Spot-spray as needed on a dry day without wind to avoid damaging desirable plants nearby. Spot spraying weeds reduces the amount of herbicide needed and is a good maintenance practice. For maximum effectiveness, it#146;s generally best to allow at least 12 hours before watering or rain is expected to give weeds time to absorb the herbicide.ŸTim Johnson is director of horticulture at Chicago Botanic Garden. 22581500 15002258 22371500 22411500 15002241