From our perspective, the primary concern with pot life is confinement. We delphiniums develop deep, extensive root systems to anchor our tall, flower-spiked stems and to seek out moisture and nutrients. A container feels inherently restrictive. Therefore, if you wish to attempt this, you must choose a pot that accommodates our needs. Select a large, deep container—a minimum of 18 inches in both depth and diameter is advisable. This provides adequate room for our roots to establish a strong foundation, which is critical for supporting our vertical growth. Furthermore, excellent drainage is non-negotiable; waterlogged soil will lead to root rot, a condition from which we rarely recover.
The growing medium in a pot is our entire world, unlike in a garden bed where we can send roots farther to find what we need. We require a rich, fertile, and well-draining soil mixture to thrive. A high-quality potting mix, amended with well-rotted compost or a slow-release fertilizer, will provide the initial nutrients and structure we desire. The soil must retain moisture without becoming soggy. As heavy feeders, especially during our vigorous growth and blooming period in early summer, we will deplete the nutrients in the confined space of a pot quite quickly. Therefore, a consistent feeding schedule is crucial. A balanced, water-soluble fertilizer applied every two to three weeks during the growing season will help sustain our energy for producing those iconic flower spikes.
Our requirements for sunlight remain unchanged in a container: we need a minimum of six to eight hours of full sun daily to fuel our growth and flowering. However, potted life makes us more vulnerable to environmental stresses. The soil in a container heats up and dries out much faster than garden soil. You must be vigilant about watering, likely daily during hot, dry spells, ensuring moisture reaches our deep roots. Perhaps the greatest physical challenge we face is stability. Our hollow stems growing several feet high act like sails, making us top-heavy and extremely susceptible to wind. A large, heavy pot provides some bottom weight, but you will almost certainly need to stake us early in the season. A robust support system, such as a grow-through grid or individual stakes, is essential to prevent our stems from snapping.
It is important to remember that we are perennial plants. While an annual might complete its lifecycle in a single season in a pot, we intend to return for several years. Overwintering in a container presents a significant challenge. Our root systems are far more exposed to freezing temperatures in a pot than in the insulating ground. In climates with cold winters, the entire container may freeze solid, which can be fatal. To improve our chances of survival, you could move our pot to an unheated garage or sheltered location after we have died back in the autumn. Alternatively, insulating the container by wrapping it in bubble wrap or burying it in the ground can help protect our roots from extreme cold.
