Annuals that play it cool

  • Article by: MARY HOCKENBERRY MEYER , Special to the Star Tribune
  • Updated: April 10, 2008 - 5:27 PM
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Osteo Asti White, is a cool-season annual.

Photo: All-American Selections

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If you're longing for color -- and frankly, who isn't -- consider planting some cold-tolerant annuals. Many of these rough and ready bloomers can be planted as soon as the soil can be worked. And, unlike so many other annuals, they actually grow best in cooler weather.

Starting from seed, sow calendula, sweet pea and bachelor's button directly into the cool soil. Other cold-tolerant annuals are best when purchased as plants and potted in a planter box or decorative pot by your front door.

So, do what the pros do: Plant these cool annuals early and replace them in June with a new batch of annuals that can take the heat.

TRIED AND TRUE

Old-fashioned favorites such as pansies, violas, sweet peas, dianthus, bachelor's buttons, snapdragons and calendula really like cool weather. In fact, they'll even tolerate a frost. But once the temperatures top 75 degrees, they may not be at their best. So plant them early and enjoy them while they last.

PANSIES AND VIOLAS

With their cheerful, colorful faces, pansies and their smaller, often single-colored cousins, violas, have long been used to give a not-so-warm welcome to spring. Temperatures of 80 degrees or more can stop pansies from flowering, even when they're planted in an ideal site (full sun and moist soil).

While few pansies survive our hot summers, they bloom beautifully in the fall when planted in late August or September. And if they're covered with a thick layer of winter mulch, they can survive the winter to bloom early the following spring, even in Zone 3.

SWEET PEAS

Few flowers are as wonderfully fragrant as sweet peas. But most years, it can get too hot in Minnesota for these prolific bloomers to last well into summer.

Sweet pea seeds have a tough cover or seed coat. Before you plant them, soak the seeds overnight. If the dark brown seed coats are still intact, use a knife to nick the seeds, so they will take up water and grow.

Sow sweet peas outdoors as soon as you can work the soil. These climbing plants need support, so attach string or wire from the soil to a trellis or fence.

CALENDULA

Kids can join in the fun of planting calendula, because the large seed is easy to handle. Although the foot-tall plants sometimes can bloom all summer with yellow, orange and gold flowers, they don't like heat and will stop flowering or even growing in hot weather.

If plants survive to fall, they can bloom again. They also can self-seed and come up the following spring.

NEW AND UNUSUAL

You don't have to rely only on plants your grandmother grew if you want to plant early. There are plenty of new and little-known plants that do well here in spring and fall.

DIASCIA

Covered with hundreds of small flowers in shades of pink or red, diascia (dye-ASS-ee-uh) needs no deadheading, and trails over the edge of containers for a soft flowing effect. This plant, which hails from the snapdragon family, also is known as twinspur. (Its common name refers to the two tiny spurs on the back of the lower flower petals.)

Although it doesn't tolerate as much cold as pansies or calendula (it grows best when temperatures are in the 40s and 50s), diascia is a bit better at tolerating heat and can flower all summer.

Look for Diascia 'Diamonte Coral Rose,' a 2006 All-America Selections winner, or Diascia 'Flying Colors Red.' Each grows 12 to 14 inches tall in full sun or part shade.

FLOWERING KALE AND CABBAGE

OK, these plants aren't new, but there is renewed interest in growing them. Sold in early spring and fall, these tough plants easily tolerate frost and temperatures in the low 20s.

Their color comes from the foliage that develops best in cool weather, when they really shine. These die-hard plants make a great choice for containers at the cabin, where they may get little attention.

'Palm Tree' kale (also known as Dinosaur or Lacinato kale) has huge gray-blue leaves that stand out in a flower border. Like all flowering kale and cabbage, it's edible, but tastes best when the plant is immature.

OSTEOSPERMUM

Also known as osteos or cape daisies, these showy daises grow 12 to 18 inches tall and sport yellow, gold or purple flowers with a dark purple or almost black center.

Native to South Africa, they love temperatures in the 50s to 70s, although recent introductions are said to be more tolerant of summer heat.

Plant cape daisies along with pansies this spring. Check out the new Osteospermum 'Asti White,' an All America Award winner from 2008, which boasts bright white flowers.

For a list of more cold-tolerant annuals, go to www.extension.umn.edu/distribution/horticulture/DG8464.html.

Mary Hockenberry Meyer is a professor and Extension Horticulturist with the University of Minnesota.

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