After moving from an Iowa acreage to a lot in the city, Jan Riggenbach depends on big, bushy annuals to fill the temporary gaps in her new landscape. Her latest book is Your Midwest Garden: An Owner’s Manual.

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Fill in the Blanks with Shrubby Annuals
by Jan Riggenbach       #Annuals   #Ornamentals   #Shrubs

The scarlet-orange daisies of Mexican sunflower provide a haven for butterflies.

I can’t wait for shrubs to fill the bare spots in a new landscape. So I don’t!  Instead, I plant some select annuals that quickly grow into big, bushy plants that can fill the void in a matter of weeks.

Castor bean
Castor beans (Ricinus communis), for example, turn into a wonderful privacy hedge, growing quickly from big, easy-to-plant seeds. When we moved to a new lot, I planted some purple-leaf castor beans along the side boundary. Neighbors were amazed how big the plants grew in a single season. And by the end of the summer, passers-by were exclaiming over what some called a “beautiful Japanese maple hedge.”

The plants vary in size depending on variety, but most grow at least 6 feet tall and wide, some much taller. In earlier times, their huge fan-like leaves earned them the name palm of Christ. They come in your choice of red or purple leaves, with varying colors of flowers and stems.

One of the most popular morning glories, ‘Heavenly Blue’ is a vigorous, quick-growing vine with blue blossoms.

Castor bean plants are rarely available at garden centers, but that’s no problem. You can buy packets of the big seeds, which are easy to handle and quick to sprout. Plant them directly in the ground in May after danger of the last spring frost, or give the seeds a head start indoors in March if you’re really eager for your new “hedge.”

Some people object to growing annuals because of having to replace the plants every spring, but there’s no extra cost here. You can simply clip dry seed heads from the plants in autumn and save them for replanting the following spring. Sometimes, castor beans even self-sow, if you allow some seeds to fall to the ground. (Beware, though, if you have kids or pets that might be attracted to the seeds: castor beans are poisonous.)

An old-fashioned annual with a charming name, kiss-me-over-the-garden-gate produces arching sprays of pink flowers atop large, heart-shaped leaves.

Plants for cutting
Although the majority of today’s annuals grow in the shape of little mounds, such as Petunia and marigolds (Tagetes spp.), a handful of others offer quick, inexpensive relief for a young landscape.

When the landscape needs some quick bushy “shrubs,” another of my go-to annuals is Mexican sunflower (Tithonia rotundifolia). These plants grow 4-6 feet tall and about as wide, and are covered with scarlet-orange daisies that are adored by butterflies. The big daisies also make excellent cut flowers. Mexican sunflowers grow well in hot, dry sites and need no coddling.

Tall varieties of annual sunflowers (Helianthus annuus) have plenty to offer in colorful flowers, seeds for birds, and heights up to 5-6 feet. For the most shrub-like shape, choose branching varieties, such as ‘Autumn Beauty’, ‘Moulin Rouge’, or ‘Strawberry Blonde’, rather than single-stem varieties.

Romantic thoughts
I think I’d want to grow kiss-me-over-the-garden-gate (Persicaria orientalis, formerly Polygonum orientale) even if I didn’t love its arching spikes of small pink flowers and its big, heart-shaped leaves. Just the name of this heirloom annual makes me smile. You get the idea: The stately plant shoots right up to 5-6 feet, tall enough to rise above almost any garden gate. And kiss-me-over-the-garden-gate is very good at self-seeding for future years.

Masses of large, airy flowers decorate spider plants.

Prolific bloomer
Spider flower (Cleome hassleriana) is another old-fashioned annual with a shrubby shape. Size varies by variety, of course, but it’s not unusual for this annual to grow 4-5 feet tall. The dramatic plants are covered with masses of large, airy flowers in blends of pink, purple, rose, or white that are a favorite for cutting.

Ornamental tobacco
Woodland tobacco (Nicotiana sylvestris) shows off best in the evening. Although the white tubular flowers are droopy by day, at night the blossoms stand at attention, attracting hummingbird moths and emitting their sweet perfume. These bushy plants grow 4-6 feet tall.

Unlike most cockscombs, ‘Cramer’s Amazon grows into an impressive 5- or 6-foot tall plant.

Most cockscombs (Celosia spp.) don’t approach the size of a shrub, but one called ‘Cramer’s Amazon’ (C. argentea) grows an impressive 5-6 feet tall and 3-4 feet wide. The spiky flowers are an almost fluorescent magenta and are excellent for bouquets. Like other cockscomb varieties, it’s easy to grow. Just be sure to allow extra time to search for a source of the sometimes elusive seeds or transplants.

Best of the rest
‘Purple Majesty’ millet (Pennisetum glaucum) is an easy-to-grow annual ornamental grass that grows 4-5 feet tall in one season. It features bright purple leaves and flower stalks.

Lantana (L. camera) has occupied a soft spot in my heart since our first year on an acreage in Iowa. The area was suffering a severe drought, and grasshoppers ate almost everything I planted. But they didn’t touch the scented foliage of the lantanas. Butterflies, on the other hand, flocked to the flowers.

I’ve kept lantanas going ever since, cutting them back every autumn enough to fit into 6-inch pots for wintering indoors under lights. Their mature size varies, but in years with ample moisture, some grow into bushy plants 5 feet tall and wide. Their multi-colored flower clusters are always a delight.

Even some kinds of coleus (Plectranthus scutellariodes) grow big enough to have a real presence in the landscape. Some big, bushy varieties that help fill landscape gaps include ‘Burgundy Sun’, ‘Saturn’, and Colorblaze Marooned.

A Vine Way to Screen the Scene
With the help of a trellis or fence for support, annual vines can provide quick shade or privacy, while you wait for permanent plantings to grow.

Morning glory (Ipomoea spp.) is a quick-growing favorite that reaches 8-20 feet tall and blooms in blue, crimson, lavender, pink, violet, white, or bicolor, depending on which variety you choose. Soak the seeds overnight to soften the hard seed coat before planting in the garden after danger of frost.

Here are a few other annual vines that grow quickly from seed to offer quick cover:

• Purple hyacinth bean (Dolichos lablab) boasts striking lilac-colored blossoms, shiny purple pods, purple-veined leaves, and purple stems.

• Cypress vine (Ipomoea quamoclit) comes in your choice of red or white flowers adorning ferny foliage.

• Climbing nasturtium (Tropaeolum majus) varieties, such as ‘Jewels of Africa’ or ‘Spitfire’, perk up the landscape with their bright, sunny colors. The plants thrive in poor soil.

• Moonvine (Ipomoea alba) shows off at night with its huge, white blossoms.


A version of this article appeared in a May/June 2016 print edition of State-by-State Gardening.
Photography courtesy of Jan Riggenbach.


Posted: 06/11/18   RSS | Print


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