The Perennial Care Manual by Rob Cardillo

Author:Rob Cardillo
Language: eng
Format: epub
Publisher: Storey Publishing
Published: 2009-06-14T16:00:00+00:00

DEFINITELY DEADHEAD Where crocosmias thrive, they may actually grow too enthusiastically, to the point of being aggressive in the garden and even invasive in some regions. In mild areas, it’s a good idea to snip off the seedpods to prevent self-sowing.

Delphinium

DELPHINIUM

The elegant spires of well-grown delphiniums are a treat to the eye, but that beauty definitely isn’t the easy-care kind — at least in most areas.

THESE PERSNICKETY PERENNIALS grow best in areas with relatively cool summers and low humidity; elsewhere, they may last just a year or two and never quite reach their full glory. Still, they can be so stunning that for many of us even a few weeks of bloom is worth any amount of effort. Species and selections that bloom in shades of blue are usually most enticing, but you can find whites, pinks, and other colors, too. The spikelike flower clusters bloom over lobed green leaves.

The Elatum Group (also known as Elatum hybrids) includes most of the classic border delphiniums, which can grow anywhere from 4 to 7 feet (1.2 to 2.1 m) tall. Selections in the Belladonna Group (also listed as Delphinium × belladonna) also produce large spikes, but on more compact plants — typically 3 to 5 feet (90 to 150 cm) — that also tend to be more vigorous and longer lived. Chinese delphiniums (D. grandiflorum), such as ‘Blue Butterfly’ and ‘Blue Mirror’, are even shorter — usually just 1 to 2 feet (30 to 60 cm) tall — with deeply cut foliage. They, too, tend to be more heat tolerant than the traditional tall hybrids, but they may last only 1 or 2 years. Delphiniums are generally recommended for Zones 3 or 4 to 7.

GROWING TIPS

Light & soil. Delphiniums tend to bloom best in full sun, but they can benefit from a site with morning sun and some afternoon shade or light all-day shade south of Zone 5. Evenly moist but well-drained soil that’s enriched with compost and has a near-neutral to somewhat alkaline pH is ideal.

Division & propagation. Where delphiniums thrive, divide them every 2 to 4 years in spring to keep them vigorous. In less ideal areas, the plants may simply die out after a few years (or even just one), so it’s smart to plan ahead for replacements. Take stem cuttings in early to midspring, or grow new plants from seed; freshly collected seed gives the best results. Sow the seed outdoors any time from late summer to early spring, or indoors in mid- to late winter; barely cover it with soil or seed-starting mix. (If no sprouts appear after a few weeks indoors, enclose the pots in plastic bags, refrigerate them for about 2 weeks, and then move them back to a bright place for germination.)

Potential problems. Delphiniums are prone to a wide variety of pests and diseases, including aphids, caterpillars, leaf miners, spider mites, leaf spots, and viruses. For details on a few of the most common problems, see Troubleshooting, page 198.

SEASONAL CARE

Spring

Set out new plants, or move or divide existing clumps, in early spring.

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