Annual Flowers to Fill Your Borders
by: Sara Raab

We all know that for permanence in the garden and diversity of flower and foliage, perennial plants can't be beat. However, the perennial that blooms all summer is a rare one, and a bed or border restricted to hardy plants often lacks that certain punch that only annuals can deliver.

Here at Olbrich, we have found that incorporating certain annuals into our perennial plantings helps to fill in spatial gaps between plants as well as temporal gaps in the successive bloom times of perennials. We rely on annuals to complement and enhance a color scheme and to provide season-long interest.

This type of interplanting can be especially effective in a newly planted perennial garden or recently revamped area. In order to avoid overcrowding in a few year's time, perennials need to be spaced in accordance with their mature sizes.  However, for the first one or two seasons, this may leave you with a bed of mulch peppered with tiny plants that are busily establishing their roots but not yet sending out the lush foliage and blooms that you were hoping for.

In planting our new Sunken Garden last spring, I experienced this situation on a grand scale. Faced with large expanses of mulch between young shrubs and perennials, I decided to scatter small groupings of annuals throughout the garden to fill blank spaces that will be green in a few years time.

One of my favorite flowering tobaccos for the mixed border is 'Daylight Sensation' (Nicotiana sanderae 'Daylight Sensation'). This selection bears a mixed palette of delicate pink, mauve and white star-shaped blooms that are especially beautiful in the dappled light of partial shade. The elegant flower stalks reach three feet in height, knitting into one another and neighboring plants.

The selection 'Nicki White' (Nicotiana alata 'Nicki White') stands two feet in height and is taller and airier than other cultivars of this popular species.  Small groups of three to five plants intermesh into masses of white flowers that positively glow at dusk. Like all flowering tobaccos, both of these selections will thrive in both full sun and partial shade, and are able to withstand the worst heat of summer.

The constant floral display and dense growth form of the salvias suit them perfectly to the task of filling in space within a newly planted bed. While nearly every service station in America boasts a display of screaming red salvia, I might recommend some of the more demure varieties available, unless you want to attract the attention of speeding motorists.

Few other flowers can rival the color of the selection 'Rhea' (Salvia farinacea 'Rhea') whose deep blue spikes are produced all summer long.  Standing at only 18 inches tall, this salvia is at home in the front of the border.  'Coral Nymph' is a close relative (Salvia coccinea 'Coral Nymph') which has blossoms of a rich coral color, held in open spikes that are larger and airier than those of other annual salvias.  Each of these salvias successfully shroud the
leggy stalks and ripening foliage of summer-blooming lilies.

The artemisias don't produce any flowers in our climate but provide luminous silver foliage all season, and are favorites at Olbrich. Artemisia x 'Powis Castle' forms a low, wide mound of scented foliage that quickly fills large gaps and accents both pastel and hot color schemes.

Established perennial gardens also benefit from the addition of annual plants. The narrower profile of certain annuals are perfect for this task, slipping into tight spaces without too much crowding.

The delicate lavender pom-poms of tall verbena (Verbena bonariensis) should be a staple in every garden. With virtually leafless square stems that disappear against a green background, the clouds of flowers appear suspended in mid-air. Tall verbena will artistically self-seed throughout your garden for years to come, and may teach you a lesson about plant placement!

Both poppies and larkspur are self-seeding annuals that complement any established perennial garden without taking up a lot of room. The silky, ruffled petals of Shirley poppy (Papaver rhoeas) float like gauze and are available in both vibrant red and soft pastel mixes.

'Blue Cloud' larkspur (Consolida regalis 'Blue Cloud') carries hundreds of tiny bright blue flowers in a frothy cloud that provides fantastic color and textural contrast. Thin stems make this plant almost unable to cast a shadow, and it's shallow roots are unlikely to crowd its neighbors.

To bring an instant sense of the old-fashioned to your garden, you could plant Ammi majus, the white lace flower. Round, lacy disks float atop three foot stems like a bolder version of Queen Anne's lace. These flowers bring unexpected movement to the garden as they nod and sway on any chance of a breeze.

The frilly, mounded blooms of pincushion flower (Scabiosa atropurpurea) sit like dainty pincushions on long stems. Available only in mixed colors for many years, there now are recently available single-color selections. 'Ace of Spades' bears flowers of a striking deep maroon color that is almost black, while 'Blue Cockade' is an heirloom selection of medium blue. This plant is a reknowned butterfly attractor and easily squeezes between existing perennials.

Like its relatives hollyhock and lavatera, striped mallow (Malva sylvestris x 'Zebrina') is tall and sturdy, boasting open, cup-shaped flowers. These pale lavender blooms are veined with dark purple and are a sight for sore eyes in mid-August.

Experimenting with annuals allows you the kind of creativity and freedom that eight-dollar perennials
don't -- take advantage of it!