April is a significant transitional month in the gardening season, often tempting gardeners to begin planting flowers. Whether you can plant flowers in April depends entirely on your geographical location and the specific type of flower being considered. This time requires careful assessment of local environmental conditions to ensure plant survival and successful growth.
Assessing Local Climate and Soil Temperature
Successful April planting is determined by the conditions of the ground, not the calendar date. Gardeners must first determine their region’s Last Expected Frost Date, the average date after which a freeze is unlikely to occur. This date, often found through local extension offices or USDA hardiness zones, serves as a general guideline. However, unseasonable cold snaps can still happen well after this time.
Soil temperature is a more reliable measure than air temperature for determining planting readiness. Cold soil inhibits seed germination and causes newly planted seedlings to become stagnant and weak. For many cold-tolerant seeds, a minimum soil temperature of 45 to 50 degrees Fahrenheit is necessary for successful sprouting and root establishment. Using a soil thermometer provides a precise measurement, allowing decisions to be based on current conditions rather than historical averages.
Hardy Annuals and Perennials for Direct Planting
Once the ground begins to warm, a variety of cold-tolerant flowers can be planted directly into garden beds in April. These hardy annuals and perennials withstand the cooler soil and air temperatures of early spring. Hardy annuals, which complete their life cycle in one season, can often be direct-sown as seed this month.
Flowers suitable for immediate planting include hardy annuals such as calendula, cornflowers, and sweet peas. These plants tolerate light frosts and establish strong root systems in cool soil, leading to robust growth and earlier blooms. Resilient perennials like Black-eyed Susan, Shasta Daisy, and Yarrow can also be planted as bare-root or potted plants.
When sowing seeds, follow the packet instructions for depth, often planting them at one to two times the seed’s diameter. Proper depth ensures seeds receive enough moisture and are not washed away. It also provides adequate sunlight for germination in varieties like Shasta Daisy and Columbine. Hardy bulbs, such as certain lilies, can also be planted in pots or directly into the ground this month.
Preparing Tender Transplants
While hardy varieties can be planted in April, heat-loving flowers started indoors, known as tender transplants, require a careful transition before being moved outside permanently. This process, called “hardening off,” acclimates the plants to the harsher outdoor environment, including fluctuating temperatures, wind, and direct sunlight. Without hardening off, these delicate indoor-grown plants can suffer transplant shock, wilting, sun scald, or death.
The hardening off procedure should begin about two weeks before the expected safe planting date for tender annuals like impatiens, petunias, and marigolds. Initially, plants are placed outside in a sheltered, shady location for two to three hours when temperatures are above 45 to 50 degrees Fahrenheit. The duration of exposure and the intensity of sunlight are gradually increased over the 7- to 14-day period.
By the end of the two-week period, plants should tolerate spending 24 hours outdoors, allowing their cell walls to thicken and their growth habit to become firmer. During this time, watering frequency is reduced, and fertilizing is suspended to prepare the plants for the less-controlled garden environment. This preparation ensures that when soil and air temperatures are consistently warm enough, the transplants thrive immediately upon planting.