Oxalis, commonly known as wood sorrel or shamrocks, are popular ornamental plants cultivated for their distinctive foliage and delicate flowers. These plants grow from underground storage structures, typically corms or small tubers referred to as bulbs. Determining the optimal planting time relies heavily on two primary factors: the intended growing environment and the specific genetic variety of the plant.
Distinguishing Hardy and Tender Oxalis Varieties
Oxalis varieties are separated into two groups based on their tolerance for cold temperatures. “Hardy” types are capable of surviving freezing temperatures and successfully overwintering in garden soil, often relying on mulch for protection in colder regions. These varieties are typically planted to establish a permanent presence for the spring and summer growing seasons.
Conversely, “tender” varieties are highly sensitive to frost and must be protected from cold weather, often requiring them to be lifted from the ground or grown exclusively indoors. For example, the popular purple-leafed Oxalis triangularis is generally considered tender, while types like Oxalis deppei (the “Iron Cross” shamrock) can be managed as hardy in milder climates. Misclassifying a tender variety and exposing it to hard frost will result in the destruction of the bulb.
Optimal Timing for Outdoor Planting
For hardy Oxalis varieties planted outdoors, timing is directly linked to local climate conditions. The recommended approach is to plant the bulbs in early spring as soon as the threat of a hard frost has reliably passed. This allows the corms to initiate growth and develop foliage as soil temperatures begin to rise.
A more precise indicator than the calendar is the soil temperature, which should be consistently above 50°F (10°C) for several days. Planting into soil that is too cold can lead to sluggish growth or rotting before roots can properly form. Consult regional gardening resources to determine the average date of the last expected frost.
Alternatively, planting can occur in the fall, provided the bulbs are set into the ground approximately six to eight weeks before the first expected severe freeze. This window allows the Oxalis to develop a robust root system capable of sustaining it through winter dormancy. Fall planting ensures the established root structure is ready to support rapid top growth and blooming once spring arrives.
Scheduling for Indoor Container Planting
When cultivating tender Oxalis varieties in indoor containers, the planting schedule is flexible since the environment is controlled. Bulbs can be started almost any time of the year, allowing growers to manipulate the plant’s growth and flowering cycles. To achieve continuous growth throughout the standard season, the best time to plant is typically late winter or early spring.
Planting at this time utilizes the naturally increasing day length and light intensity of spring to encourage strong foliage development and minimize the need for artificial light supplementation. This timing helps the plant synchronize with the annual light cycle, resulting in more vigorous initial growth.
A common practice for displaying blooms at a specific time, such as during the winter holidays, is called forcing. This involves planting the bulbs approximately eight to ten weeks before the desired flowering date. The consistent indoor warmth and light allow the cycle to be jump-started, ensuring the plant reaches its peak ornamental value precisely when needed.
Managing Dormancy and Replanting Cycles
Oxalis requires a period of dormancy to rest and recharge its energy reserves, whether grown indoors or outdoors. This rest cycle is signaled when the foliage begins to yellow and collapse after active growth. At this point, watering should be significantly reduced. The container or bulbs should be moved to a cool, dark location where temperatures remain between 50°F and 60°F (10°C and 15°C).
The duration of this rest period typically ranges from six to twelve weeks. To restart the growth cycle, the bulbs are brought back into a brighter, warmer environment and watering is resumed. This shift simulates the onset of spring and cues the corm to break dormancy, beginning the production of new shoots and leaves.