Successful flower planting in Chicago requires understanding the local climate and the temperament of the chosen plants. Gardeners must pay close attention to average temperature fluctuations to ensure flowers thrive. This article provides a timeline for planting various flowers to maximize your garden’s display.
Understanding Chicago’s Planting Calendar
The Chicago planting season is governed by the average last spring frost date, which serves as the boundary between safe and risky planting. Chicago is located primarily within USDA Hardiness Zones 5b and 6a. This classification means most delicate plants cannot survive the winter outdoors. The city’s proximity to Lake Michigan creates a microclimate that can delay spring warming, often prolonging the threat of frost later than in surrounding areas. The average last frost date is generally around the middle of May.
Timing for Tender Annuals and Transplants
The majority of popular summer flowers are classified as “tender annuals,” meaning they cannot withstand freezing temperatures and require warm soil to grow vigorously. The safe window for planting these flowers as transplants is after the average last frost date, typically from mid-May onward. Many gardeners wait until after Memorial Day weekend to ensure the soil has warmed sufficiently for root establishment.
Planting too early can stunt the growth of heat-loving flowers like Petunias, Impatiens, Begonias, and Zinnias. Soil temperatures must reach at least 60 degrees Fahrenheit for optimal root development. Before moving transplants into the garden, “harden them off” by gradually exposing them to outdoor conditions over seven to ten days. This slow exposure prevents transplant shock.
Scheduling Cold-Tolerant Flowers and Direct Seeding
A group of flowers known as “hardy annuals” can be planted much earlier because they tolerate cooler soil and light frost. Gardeners can begin planting these varieties four to six weeks before the last expected frost date, often in early to mid-April. This early start allows the plants to establish a robust root system before the summer heat arrives.
Cold-tolerant flowers planted as transplants in early spring include Pansies, Violas, Snapdragons, and Ornamental Kale. These plants thrive in cool, moist conditions and will continue to bloom until the heat of mid-summer causes them to fade. Flowers that benefit from direct seeding include Poppies, Calendula, and Nigella. These varieties often require cool, moist soil for germination, a process known as cold stratification. Direct-sow varieties should be planted as soon as the soil is workable and can handle the light frosts common in April.
Preparing for Next Spring
The annual planting cycle requires addressing the needs of next season’s earliest blooms. Spring-flowering bulbs, such as Tulips, Daffodils, and Crocuses, need a period of cold dormancy to initiate flowering. The optimal window for planting these bulbs is in the fall, typically from late September through October.
Bulbs should be planted before the ground freezes solid, ensuring roots develop anchor roots before deep winter. Late summer and early fall are also the best times for dividing and transplanting established perennial flowers. Moving spring and summer-blooming perennials, such as Peonies, in September allows divisions six weeks to establish new root growth before winter rest.