Pentas (Pentas lanceolata) and lantana (Lantana spp.) are two of the best flowers for attracting butterflies. They both thrive in hot, sunny locations and come in matching shades of red, orange, purple, pink, yellow and white -- in short, they are made to grow together. Pentas and lantana are both tender perennials, hardy in U.S. Department of Agriculture plant hardiness zones 9 to11, but are commonly grown as annuals in colder zones.
Choose a location for planting with at least four hours of sun each day. Neither plant is very particular about soil type. Pentas and lantana tolerate partial shade but have the best flower display when planted in full sun. Both species are large sprawling plants, especially lantana, and are inappropriate for small flowerbeds unless dwarf varieties are used. At least 100 square feet of growing area is ideal for growing them together.
Spread 2 to 3 inches of compost over the planting area and mix it into the soil with a digging fork before planting. Both plants are tolerant of soils of low fertility, but will flower more profusely if there are more nutrients available. If planting in heavy clay or a low-lying area, build up a slight mound in the planting area, because neither plant will be happy if the soil is constantly waterlogged.
Consider how the growth habit of the two plants will match up when laying out the planting. In general, lantana grows wider than tall -- even the shrubby varieties. In contrast, pentas has a more upright growth habit. One of the low, spreading varieties of lantana planted in front of a border of pentas is a nice combination. If the taller lantanas are used, plant the pentas as a border in front of them.
Space the plants according to the variety. Most varieties of pentas grow 3 to 4 feet tall and wide and can be planted 18 to 24 inches apart, although dwarf varieties can be planted as close as 10 or 12 inches apart. Lantana varieties come in both shrub and ground cover forms. However, most varieties grow 4 to 6 feet wide, no matter the form. Lantana can be planted on 3 to 4 foot spacing and allowed to grow together as a mass planting. However, like pentas, dwarf forms of lantana grow to only 12 or 16 inches tall and can be spaced just 1 foot apart.
Plant in spring. Fertilizer is not necessary if the soil has been enriched with compost prior to panting. Fertilizer can actually reduce flowering in lantana and lead to problems with pest and disease. Both plants are moderately drought tolerant, but spread several inches of mulch over the planting area to conserve soil moisture. Water only after the top 1 inch of soil becomes dry.
Allow the plants to grow freely through spring, summer and fall, but cut them back as needed to prevent them from sprawling into pathways or other beds -- this is likely with lantana as it is an especially vigorous grower. Pentas and lantana will continue flowering until the first frost. A hard freeze will cause them to lose most of their leaves. After this occurs, cut them back heavily -- up to 75 percent of the growth can be removed. This keeps the plants compact and bushy the following year in areas where they are perennial.