Crocosmia are vibrant perennials that produce fiery, arching sprays of flowers from mid-summer into fall, making them a popular choice for adding late-season garden color. These plants grow from underground storage organs known as corms. The ideal window for planting these corms is during the early spring, allowing for optimal root establishment before summer heat arrives. While early planting ensures the best results, it is often still possible to successfully plant Crocosmia later in the season, depending on your local climate.
Optimal Planting Time and Method
Planting Crocosmia corms should ideally occur in the spring, once the danger of the last hard frost has passed and the soil has begun to warm up. Targeting a soil temperature of at least 50°F (10°C) is beneficial, as these plants require warmth to initiate strong growth. This early timing allows the corms sufficient time to develop a robust root system, which is necessary to support the summer foliage and subsequent flower production.
The corms should be placed in a location that receives full sun to partial shade and features moist, yet well-drained, soil. Poor drainage can easily lead to corm rot, so amending heavy soils with organic matter like compost is necessary. Plant the corms with the pointed side facing upward, setting them approximately 3 inches deep and spaced 6 to 8 inches apart. Immediately after planting, a thorough watering helps settle the soil and encourages initial root formation.
Defining the Risk of Planting Late
Missing the optimal early spring window significantly increases the risk of a reduced or absent floral display during the current growing season. The primary consequence of late planting (late spring or early summer) is the lack of time for the corm to generate necessary energy reserves. The plant must first establish an extensive root system before it can support the energy-intensive process of flowering.
If a corm is planted when the season is well underway, it may struggle to establish a strong root network before intense summer heat or drought. A poorly rooted plant is also more vulnerable to the damaging effects of winter cold before dormancy. Planting becomes too late when soil temperatures are excessively high, which can stress the corm and potentially lead to rot or failure to sprout. The objective shifts from securing a first-year bloom to simply ensuring the plant’s survival through the first winter.
Strategies for Late Season Success
If planting has been delayed, a few proactive steps can increase the odds of successful establishment. One effective technique is pre-sprouting the corms indoors a few weeks before planting them into the garden. Placing the corms in a tray of slightly damp potting mix helps start the growth process, giving them a head start before outdoor exposure.
Planting Crocosmia in containers provides another layer of control for late-season planting, especially in regions with unpredictable weather. Containers allow for easier management of soil moisture and temperature, and they can be moved to a sheltered location if the summer is excessively hot. Ensuring adequate watering is necessary, as newly forming roots cannot yet access deep soil moisture. A layer of organic mulch will help retain moisture and keep the soil temperature cooler during the hottest months.
For corms planted late, the focus must shift to securing the plant for the following year, rather than expecting a reliable bloom in the current season. Since late-planted corms have less time to store energy, they are more susceptible to winter damage than established clumps. In colder zones, applying a thick layer of mulch in late autumn provides insulation to protect the less-established corms from deep frost. Container-grown Crocosmia should be moved to an unheated garage or protected area for the winter to prevent freezing.