From our perspective, your choice of container is paramount. We delphiniums develop deep, extensive taproots to anchor our tall, flower-laden spires and seek out moisture and nutrients. A pot that is too shallow will feel like a prison, causing us to become root-bound, stressed, and unstable. To truly thrive, we require a deep pot—a minimum of 18 inches in depth and 12-18 inches in diameter is ideal. This gives our roots the room they crave to explore and establish a strong foundation. Furthermore, the container must have excellent drainage holes. Our roots despise sitting in soggy, waterlogged soil, as it quickly leads to rot, a condition from which we seldom recover.
We cannot simply grow in heavy garden soil; it compacts in containers, suffocating our roots and hindering drainage. We require a specific growing medium that mimics the well-draining, fertile conditions we love. A high-quality, peat-free potting mix is an excellent base. To make it even more to our liking, we would be grateful if you amended it with some compost for nutrient retention and a handful of perlite or coarse grit to ensure the structure remains open and free-draining. This creates an airy, moisture-retentive yet well-draining environment where our roots can breathe, access water, and absorb nutrients efficiently, promoting vigorous growth.
We are sun-worshipping plants at our core. To fuel our growth and produce our magnificent flower spikes, we need a minimum of 6 to 8 hours of direct sunlight daily. Please place our pot in the sunniest spot you have. However, our root systems in containers are more vulnerable to temperature swings than those in the ground. During a heatwave, the pot's sides can heat up excessively, literally cooking our delicate roots. A strategic placement where our roots are shaded (perhaps by other plants or a light-colored pot) while our foliage remains in the sun is perfect. In winter, our pots need protection from freezing solid, which can be fatal.
Growing in a pot means we have limited access to nutrients; we rely entirely on you for sustenance. At planting time, a slow-release fertilizer mixed into the soil will give us a good start. Once we begin our rapid growth spurt in spring, we are heavy feeders. A balanced liquid fertilizer applied every two to three weeks will provide the energy needed to build our impressive height and blooms. Regarding water, our thirst is significant, especially when we are large and the weather is hot. The goal is consistently moist soil, never bone dry and never swampy. Check our soil daily; water deeply when the top inch feels dry, allowing the excess to drain away completely.
After our spectacular first bloom, you can encourage a second, smaller show of flowers by cutting the spent flower spikes back to a side shoot. As perennials, we will eventually die back to the ground in autumn. At this point, you can cut our stems down. It is crucial to remember that we are less hardy in pots. To survive the winter, our crown and roots need insulation. Moving the pot to a sheltered location against a house wall or wrapping the pot in horticultural fleece or bubble wrap will protect us from the coldest temperatures, allowing us to burst back into life for you the following spring.
