If you want to grow a beautiful delphinium flower, let me suggest you stick to a few basic techniques.
Basic techniques for growing Delphinium
The first is to give this plant full sunshine. Reduce the sunlight, and you’ll reduce either the size or the quality of the bloom.
The second is to understand this plant is a greedy feeder. It is one of the few perennials that thrive on a little extra food without getting long, leggy, and falling over. The easiest way to do this is to toss an extra shovel of compost around each plant in the spring.
Or, give the plant a monthly watering with liquid fish emulsion. Either of these gardening tips will work. What is clear is that if you don’t feed this plant, it will not grow as big or have as many flowers as it could.
Overfeeding with nitrogen will shorten the lifespan of the flowers, so don’t overdo it with chemical fertilizer and think you’re doing a good thing.
Third, it does help to stake each delphinium flower. These flower stalks are going to be in the 5-6 foot tall range, and a little support goes a long way.
I use old Christmas tree branches stuck at the base of the plant. This gives the first few feet of growth adequate support but doesn’t stand out like a sore thumb in the garden.
Mind you; it also helps not to plant them in a direct windy garden location in the first place.
Starting your own seed is not overly difficult. The seed does require a pre-chilling to get a reasonable germination rate. Some gardeners suggest you put the seed in the freezer for a week or two to chill it.
Putting dry seed in a refrigerator is often a very good way to kill it.
Instead, put the seed in a baggie with a handful of just-damp vermiculite. Put this baggie in the crisper of the frig for 90 days, then sow the seed.
Space the delphinium flower seed 3/4-inch apart in the flower pot when sowing. Barely cover the seed – the objective is to keep the damp soil around the seed, not eliminate all light. Keep the soil damp – not swampy.
Always water with warmish water. You’ll see germination in 14-21 days.
Transplant into individual pots when the seedling has 4 true leaves (not the first seed leaves). Grow cool at 55-60 F in full sunlight to avoid stretched ugly plants.
The delphinium flower will not emerge until the second year from seed.
When to Plant Delphinium
For optimum blooming, you should plant your bulbs just before the first hard frost. Delphinium will usually do well in even moderately cold temperatures, so you can begin planting them a month before most other plants.
The earliest you can plant delirium in zone 9b is February. You should make sure your garden has been thoroughly prepared by removing existing foliage and ensuring the soil is well rotted before planting.
Delphiniums love moist soil and thrive in low fertility except in full sun, but they do equally well in the shade.
Delphiniums are drought tolerant plants and do well in areas lacking soil drainage, such as rock gardens. Most flower growers will not plant their seeds directly onto concrete or slate, but I have found it to work for some.
Planting baskets, tubs, and tubs filled with well-rotted garden compost also work well for this plant.
Be careful with Delphinium seeds. The seed pods are tiny and contain a large number of seed particles, so just a few of the pods could sprout large numbers of seeds.
If you have not sown any seed beforehand, be sure to buy or collect your seeds from a warm, sunny location away from strong winds. Plant your seeds about a week before seeding.
A delphinium can also be divided if strong and healthy, and believe it or not, tip cuttings of delphiniums can also be rooted if you know what you’re doing. Rooting tip cuttings are not for the faint of heart or beginners without equipment.
Delphinium makes excellent cut flowers (if you can stand to cut such a lovely spike) and will last upwards of 14 days from a freshly cut stem.
You can expect a delphinium flower plant to last 3-5 years in the garden without renewal, and then they’ll likely weaken and die off. Be prepared to collect your own seed and sow it as replacements.