Dahlias, celebrated for their variety of forms and colors, typically begin their growing season in the spring after the threat of frost has passed. Planting tubers when the soil temperature consistently reaches 60°F allows the plant to establish itself before summer heat arrives. This timing usually ensures a vibrant display beginning in mid-summer and continuing through the fall. However, if spring planting is missed, gardeners often wonder whether a mid-summer planting in July can still yield a rewarding season.
The Feasibility of Mid-Summer Planting
Planting dahlia tubers in July is possible, but it requires adjusting expectations regarding the bloom season. Dahlias generally require 90 to 100 days from planting to produce their first flowers, varying by variety and local climate. A tuber planted in July will have a significantly compressed growing period before the first frost ends the season. The primary trade-off for planting late is a delayed and shorter flowering window.
A dahlia tuber planted in early to mid-July will likely not begin to bloom until late September or early October, depending on the variety and the local frost date. Success depends on using firm, healthy tubers that show no signs of shriveling or rot, as they need to establish roots quickly in the heat. While the overall display will be shorter than a spring-planted counterpart, a late planting can still provide a beautiful burst of color as other summer blooms fade. Gardeners in regions with mild, late-arriving frosts will experience greater success.
Modified Planting Techniques for July
The high air and soil temperatures characteristic of July necessitate several adjustments to the typical spring planting procedure. Dahlias thrive with 6 to 8 hours of direct sun, but intense afternoon heat can cause stress and scorching. Choosing a location that receives full morning sun but offers light afternoon shade can prevent the plant from becoming heat-stressed. This protection allows the newly emerging foliage to develop without being scorched.
Immediate and deep watering is necessary for mid-summer planting, contrasting with the advice to delay watering spring-planted tubers to prevent rot. Since July soil is often warm and dry, the tuber needs immediate moisture to encourage root growth and hydration. Applying a 2 to 3-inch layer of organic mulch immediately after planting is beneficial, as it helps insulate the soil and keep feeder roots cooler. Mulch also reduces evaporation, helping the soil retain moisture lost to summer heat.
Anticipating Bloom and Tuber Development
The delayed start means flowers will appear later in the season, often coinciding with the cooling temperatures of late autumn. While dahlias planted in May peak in August and September, July-planted tubers will peak when the season is winding down. Varieties with shorter maturity times, such as smaller-flowered ball or pompon types, offer the best chance for a substantial bloom period before the frost.
A greater concern with late planting is the development of new tubers for the following season. Tuber formation depends on the plant’s ability to photosynthesize and store carbohydrates during the growing season. With a shorter overall window, the plant has less time to generate the energy required to produce robust, full-sized tubers. The resulting tubers may be noticeably smaller or less numerous than those from plants that had a full spring and summer to mature.
End-of-Season Care for Late-Planted Dahlias
Because the plants have had a shorter growing period, the newly formed tubers tend to be less mature and more susceptible to issues during winter storage. Gardeners should wait until the foliage has been blackened by the first hard frost before digging up the tubers. This period allows the plant to send its remaining energy down to the storage roots.
Once lifted, the smaller tubers require careful handling and monitoring throughout the winter. They must be cured in a dry location for a few days to harden the skin before being stored in a cool, dark location consistently above freezing. Due to their reduced size, these late-season tubers can dry out more easily than larger counterparts. Checking them periodically for shriveling or mold is necessary to ensure they survive until spring.