Plant warm-season flowering annuals, vines, herbs, and vegetables after the Chicago area’s average last frost date of May 15. Cautious gardeners often wait until Memorial Day before setting out cold-sensitive plants such as tomatoes, peppers, eggplants, and squash. Pinch back one-third of new growth to encourage stocky habit (except vines). Be sure newly purchased annuals have been hardened off properly before planting them outside. Avoid fertilizing newly planted annuals for two weeks.
Continue to plant new perennials, ornamental grasses, and roses in containers. If plant roots are root-bound (encircling the pot), make four cuts into the bottom of the root ball with a sharp tool, and flare the sections outward when planting.
Provide a gentle water drip for migrating birds. The May migrants — warblers, tanagers, orioles and buntings — are all attracted to shallow pools and the slight pinging sound of dripping water.