You can never have too many delphiniums. They are glorious plants with flower spikes that can grow up to 6 feet tall. Normally, they are a range of blues, but are also available in white, pinks, and purple. They are standouts as background plants. In the northern US and Canada, delphiniums are grown as a perennial. In the central region, from SE Montana to lower altitudes in Georgia they are usually cultivated as an annual. The Sunbelt states are typically not conducive to them, though by keeping roots cool and shading from hot sun, some gardeners have had some success.
They take full sun and well-drained soil, however they don't like being too hot or dry. In climates where temperatures exceed 90 degrees, light shade especially from the hot afternoon sun helps keep them happy. Many gardeners fertilize well in the spring and again later in the season, though adding compost and mulch may provide all the nutrients needed. Signs of nutritional deficiency are yellow foliage or stunted growth. Add a little lime to sweeten the soil, especially if you know yours is on the acidic side.
Delphiniums have a reputation for being difficult to grow. That's not necessarily so. Delphiniums can be started from seed or transplanted from nursery starts. If planting from seed, buy the best possible seed, sow in August in prepared flats, then cover lightly with a dusting of soil. Keep moist and dark to germinate. Protect by over wintering in a cold frame. Nursery starts can be transplanted in the spring as soon as the soil can be worked. Mulch to keep roots cool and moist, but don't allow them to get boggy.
You can divide existing plants early in the spring when they first come up by digging up the plant crown and cutting it into several several pieces. Each piece needs some live crown and good root.
Tall varieties benefit from being staked. Place stakes early in season to prevent damaging roots. Windbreaks like hedges or open fencing will help support them in strong winds. Shorter varieties like "Magic Fountains" are usually about 4 feet tall with sturdier stocks and are less likely to topple.
Delphiniums are large plants and need space. Don't crowd them. And don't move them when they are dormant; they don't like it and may reward your effort by dying on you.
Unfortunately, delphiniums can be susceptible to powdery mildew. Some gardeners use the same fungicides as for their roses with good result. Other gardeners swear by maintaining soil health through composting and mulching. Also, combat slugs by hand picking and destroying, or using slug bait, especially in spring when plants are just coming up.
Delphiniums bloom from June to August. They make long-lasting cut flowers, if you can bear to cut them and bring them inside. If you do cut them, remove the stalk to promote a second flowering. An old time tip to extend their bloom time is to remove seed pods as they develop and work wood ash into the soil around them.
The life expectancy of many delphiniums is often only two or three years, but occasionally they can last much longer.
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