How to Grow Calibrachoa

Pick a color, any color -- well, not brown or black -- and there's a cascading calibrachoa (Calibrachoa spp.) cultivar to match. Better known as million bells for the masses of tiny trumpet flowers that smother their mounding or trailing leaves, calibrachoas grow as perennials in U.S. Department of Agriculture plant hardiness zones 9 through 11. Elsewhere, they've come to rival petunias (Petunia spp.) as favorite sunny-garden annuals.

Unlike many petunia varieties, million bells voluntarily shed their faded flowers. No deadheading is needed to keep them tidy and covered in blooms. Plant them in spring and enjoy the symphony until the first fall frost.

In addition to its other virtues, million bells rarely suffer damage from browsing deer, according to a James City County-Williamsburg Master Gardeners survey of area residents. However, the survey warns that when they're hungry enough, deer may eat plants they normally avoid.

Million bells flower nicely in four hours of daily sun; in six or more hours, they nearly bury their stems with blooms.

Plant them in well-drained, consistently moist soil with plenty of organic matter. If your soil is on the heavy, poorly drained side, work a 3-inch layer of organic compost into its top 6 inches at planting.

Allow 12 to 15 inches between mounding varieties and 18 to 20 inches between trailing million bells varieties. As the plants fill in, they shade the soil, helping to keep it moist and discouraging weeds.

Such vigorous flowering takes energy, and fertilizer helps supply it. For easy fertilizing, consider using organic, slow-release fertilizer spikes, such as a 3-5-6 formula. Once inserted into the soil they release a slow, steady stream of nutrients over several weeks. The spikes supply nitrogen for healthy, lush foliage, phosphorus for bright, abundant flowers and potassium for strong roots.

The makers of one brand recommend inserting eight of their spikes into each 1 square foot of soil every two months during the growing season. Water the soil around the plants well. Place a fertilizer spike pointed-end-down on the soil and push down until its smooth end is flush with the soil's surface. Space spikes evenly in the soil, according to label instructions.

Fertilizers of different strengths have different application rates and frequencies. Always follow the label's application instructions for the brand you choose.

Water million bells when the top 2 inches of soil feel barely damp or dry to the touch. Overwatering exposes the plants to root rot. Water slowly and deeply around the bases of the plants, soaking the soil to the depth of the roots. Keep the leaves dry; otherwise they may attract fungal disease.